Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * multixact.c
4 : * PostgreSQL multi-transaction-log manager
5 : *
6 : * The pg_multixact manager is a pg_xact-like manager that stores an array of
7 : * MultiXactMember for each MultiXactId. It is a fundamental part of the
8 : * shared-row-lock implementation. Each MultiXactMember is comprised of a
9 : * TransactionId and a set of flag bits. The name is a bit historical:
10 : * originally, a MultiXactId consisted of more than one TransactionId (except
11 : * in rare corner cases), hence "multi". Nowadays, however, it's perfectly
12 : * legitimate to have MultiXactIds that only include a single Xid.
13 : *
14 : * The meaning of the flag bits is opaque to this module, but they are mostly
15 : * used in heapam.c to identify lock modes that each of the member transactions
16 : * is holding on any given tuple. This module just contains support to store
17 : * and retrieve the arrays.
18 : *
19 : * We use two SLRU areas, one for storing the offsets at which the data
20 : * starts for each MultiXactId in the other one. This trick allows us to
21 : * store variable length arrays of TransactionIds. (We could alternatively
22 : * use one area containing counts and TransactionIds, with valid MultiXactId
23 : * values pointing at slots containing counts; but that way seems less robust
24 : * since it would get completely confused if someone inquired about a bogus
25 : * MultiXactId that pointed to an intermediate slot containing an XID.)
26 : *
27 : * XLOG interactions: this module generates a record whenever a new OFFSETs or
28 : * MEMBERs page is initialized to zeroes, as well as an
29 : * XLOG_MULTIXACT_CREATE_ID record whenever a new MultiXactId is defined.
30 : * This module ignores the WAL rule "write xlog before data," because it
31 : * suffices that actions recording a MultiXactId in a heap xmax do follow that
32 : * rule. The only way for the MXID to be referenced from any data page is for
33 : * heap_lock_tuple() or heap_update() to have put it there, and each generates
34 : * an XLOG record that must follow ours. The normal LSN interlock between the
35 : * data page and that XLOG record will ensure that our XLOG record reaches
36 : * disk first. If the SLRU members/offsets data reaches disk sooner than the
37 : * XLOG records, we do not care; after recovery, no xmax will refer to it. On
38 : * the flip side, to ensure that all referenced entries _do_ reach disk, this
39 : * module's XLOG records completely rebuild the data entered since the last
40 : * checkpoint. We flush and sync all dirty OFFSETs and MEMBERs pages to disk
41 : * before each checkpoint is considered complete.
42 : *
43 : * Like clog.c, and unlike subtrans.c, we have to preserve state across
44 : * crashes and ensure that MXID and offset numbering increases monotonically
45 : * across a crash. We do this in the same way as it's done for transaction
46 : * IDs: the WAL record is guaranteed to contain evidence of every MXID we
47 : * could need to worry about, and we just make sure that at the end of
48 : * replay, the next-MXID and next-offset counters are at least as large as
49 : * anything we saw during replay.
50 : *
51 : * We are able to remove segments no longer necessary by carefully tracking
52 : * each table's used values: during vacuum, any multixact older than a certain
53 : * value is removed; the cutoff value is stored in pg_class. The minimum value
54 : * across all tables in each database is stored in pg_database, and the global
55 : * minimum across all databases is part of pg_control and is kept in shared
56 : * memory. Whenever that minimum is advanced, the SLRUs are truncated.
57 : *
58 : * When new multixactid values are to be created, care is taken that the
59 : * counter does not fall within the wraparound horizon considering the global
60 : * minimum value.
61 : *
62 : * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
63 : * Portions Copyright (c) 1994, Regents of the University of California
64 : *
65 : * src/backend/access/transam/multixact.c
66 : *
67 : *-------------------------------------------------------------------------
68 : */
69 : #include "postgres.h"
70 :
71 : #include "access/multixact.h"
72 : #include "access/slru.h"
73 : #include "access/transam.h"
74 : #include "access/twophase.h"
75 : #include "access/twophase_rmgr.h"
76 : #include "access/xact.h"
77 : #include "access/xlog.h"
78 : #include "access/xloginsert.h"
79 : #include "catalog/pg_type.h"
80 : #include "commands/dbcommands.h"
81 : #include "funcapi.h"
82 : #include "lib/ilist.h"
83 : #include "miscadmin.h"
84 : #include "pg_trace.h"
85 : #include "postmaster/autovacuum.h"
86 : #include "storage/lmgr.h"
87 : #include "storage/pmsignal.h"
88 : #include "storage/proc.h"
89 : #include "storage/procarray.h"
90 : #include "utils/builtins.h"
91 : #include "utils/memutils.h"
92 : #include "utils/snapmgr.h"
93 :
94 :
95 : /*
96 : * Defines for MultiXactOffset page sizes. A page is the same BLCKSZ as is
97 : * used everywhere else in Postgres.
98 : *
99 : * Note: because MultiXactOffsets are 32 bits and wrap around at 0xFFFFFFFF,
100 : * MultiXact page numbering also wraps around at
101 : * 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE, and segment numbering at
102 : * 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need
103 : * take no explicit notice of that fact in this module, except when comparing
104 : * segment and page numbers in TruncateMultiXact (see
105 : * MultiXactOffsetPagePrecedes).
106 : */
107 :
108 : /* We need four bytes per offset */
109 : #define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(MultiXactOffset))
110 :
111 : #define MultiXactIdToOffsetPage(xid) \
112 : ((xid) / (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
113 : #define MultiXactIdToOffsetEntry(xid) \
114 : ((xid) % (MultiXactOffset) MULTIXACT_OFFSETS_PER_PAGE)
115 : #define MultiXactIdToOffsetSegment(xid) (MultiXactIdToOffsetPage(xid) / SLRU_PAGES_PER_SEGMENT)
116 :
117 : /*
118 : * The situation for members is a bit more complex: we store one byte of
119 : * additional flag bits for each TransactionId. To do this without getting
120 : * into alignment issues, we store four bytes of flags, and then the
121 : * corresponding 4 Xids. Each such 5-word (20-byte) set we call a "group", and
122 : * are stored as a whole in pages. Thus, with 8kB BLCKSZ, we keep 409 groups
123 : * per page. This wastes 12 bytes per page, but that's OK -- simplicity (and
124 : * performance) trumps space efficiency here.
125 : *
126 : * Note that the "offset" macros work with byte offset, not array indexes, so
127 : * arithmetic must be done using "char *" pointers.
128 : */
129 : /* We need eight bits per xact, so one xact fits in a byte */
130 : #define MXACT_MEMBER_BITS_PER_XACT 8
131 : #define MXACT_MEMBER_FLAGS_PER_BYTE 1
132 : #define MXACT_MEMBER_XACT_BITMASK ((1 << MXACT_MEMBER_BITS_PER_XACT) - 1)
133 :
134 : /* how many full bytes of flags are there in a group? */
135 : #define MULTIXACT_FLAGBYTES_PER_GROUP 4
136 : #define MULTIXACT_MEMBERS_PER_MEMBERGROUP \
137 : (MULTIXACT_FLAGBYTES_PER_GROUP * MXACT_MEMBER_FLAGS_PER_BYTE)
138 : /* size in bytes of a complete group */
139 : #define MULTIXACT_MEMBERGROUP_SIZE \
140 : (sizeof(TransactionId) * MULTIXACT_MEMBERS_PER_MEMBERGROUP + MULTIXACT_FLAGBYTES_PER_GROUP)
141 : #define MULTIXACT_MEMBERGROUPS_PER_PAGE (BLCKSZ / MULTIXACT_MEMBERGROUP_SIZE)
142 : #define MULTIXACT_MEMBERS_PER_PAGE \
143 : (MULTIXACT_MEMBERGROUPS_PER_PAGE * MULTIXACT_MEMBERS_PER_MEMBERGROUP)
144 :
145 : /*
146 : * Because the number of items per page is not a divisor of the last item
147 : * number (member 0xFFFFFFFF), the last segment does not use the maximum number
148 : * of pages, and moreover the last used page therein does not use the same
149 : * number of items as previous pages. (Another way to say it is that the
150 : * 0xFFFFFFFF member is somewhere in the middle of the last page, so the page
151 : * has some empty space after that item.)
152 : *
153 : * This constant is the number of members in the last page of the last segment.
154 : */
155 : #define MAX_MEMBERS_IN_LAST_MEMBERS_PAGE \
156 : ((uint32) ((0xFFFFFFFF % MULTIXACT_MEMBERS_PER_PAGE) + 1))
157 :
158 : /* page in which a member is to be found */
159 : #define MXOffsetToMemberPage(xid) ((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_PAGE)
160 : #define MXOffsetToMemberSegment(xid) (MXOffsetToMemberPage(xid) / SLRU_PAGES_PER_SEGMENT)
161 :
162 : /* Location (byte offset within page) of flag word for a given member */
163 : #define MXOffsetToFlagsOffset(xid) \
164 : ((((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) % \
165 : (TransactionId) MULTIXACT_MEMBERGROUPS_PER_PAGE) * \
166 : (TransactionId) MULTIXACT_MEMBERGROUP_SIZE)
167 : #define MXOffsetToFlagsBitShift(xid) \
168 : (((xid) % (TransactionId) MULTIXACT_MEMBERS_PER_MEMBERGROUP) * \
169 : MXACT_MEMBER_BITS_PER_XACT)
170 :
171 : /* Location (byte offset within page) of TransactionId of given member */
172 : #define MXOffsetToMemberOffset(xid) \
173 : (MXOffsetToFlagsOffset(xid) + MULTIXACT_FLAGBYTES_PER_GROUP + \
174 : ((xid) % MULTIXACT_MEMBERS_PER_MEMBERGROUP) * sizeof(TransactionId))
175 :
176 : /* Multixact members wraparound thresholds. */
177 : #define MULTIXACT_MEMBER_SAFE_THRESHOLD (MaxMultiXactOffset / 2)
178 : #define MULTIXACT_MEMBER_DANGER_THRESHOLD \
179 : (MaxMultiXactOffset - MaxMultiXactOffset / 4)
180 :
181 : #define PreviousMultiXactId(xid) \
182 : ((xid) == FirstMultiXactId ? MaxMultiXactId : (xid) - 1)
183 :
184 : /*
185 : * Links to shared-memory data structures for MultiXact control
186 : */
187 : static SlruCtlData MultiXactOffsetCtlData;
188 : static SlruCtlData MultiXactMemberCtlData;
189 :
190 : #define MultiXactOffsetCtl (&MultiXactOffsetCtlData)
191 : #define MultiXactMemberCtl (&MultiXactMemberCtlData)
192 :
193 : /*
194 : * MultiXact state shared across all backends. All this state is protected
195 : * by MultiXactGenLock. (We also use MultiXactOffsetControlLock and
196 : * MultiXactMemberControlLock to guard accesses to the two sets of SLRU
197 : * buffers. For concurrency's sake, we avoid holding more than one of these
198 : * locks at a time.)
199 : */
200 : typedef struct MultiXactStateData
201 : {
202 : /* next-to-be-assigned MultiXactId */
203 : MultiXactId nextMXact;
204 :
205 : /* next-to-be-assigned offset */
206 : MultiXactOffset nextOffset;
207 :
208 : /* Have we completed multixact startup? */
209 : bool finishedStartup;
210 :
211 : /*
212 : * Oldest multixact that is still potentially referenced by a relation.
213 : * Anything older than this should not be consulted. These values are
214 : * updated by vacuum.
215 : */
216 : MultiXactId oldestMultiXactId;
217 : Oid oldestMultiXactDB;
218 :
219 : /*
220 : * Oldest multixact offset that is potentially referenced by a multixact
221 : * referenced by a relation. We don't always know this value, so there's
222 : * a flag here to indicate whether or not we currently do.
223 : */
224 : MultiXactOffset oldestOffset;
225 : bool oldestOffsetKnown;
226 :
227 : /* support for anti-wraparound measures */
228 : MultiXactId multiVacLimit;
229 : MultiXactId multiWarnLimit;
230 : MultiXactId multiStopLimit;
231 : MultiXactId multiWrapLimit;
232 :
233 : /* support for members anti-wraparound measures */
234 : MultiXactOffset offsetStopLimit; /* known if oldestOffsetKnown */
235 :
236 : /*
237 : * Per-backend data starts here. We have two arrays stored in the area
238 : * immediately following the MultiXactStateData struct. Each is indexed by
239 : * BackendId.
240 : *
241 : * In both arrays, there's a slot for all normal backends (1..MaxBackends)
242 : * followed by a slot for max_prepared_xacts prepared transactions. Valid
243 : * BackendIds start from 1; element zero of each array is never used.
244 : *
245 : * OldestMemberMXactId[k] is the oldest MultiXactId each backend's current
246 : * transaction(s) could possibly be a member of, or InvalidMultiXactId
247 : * when the backend has no live transaction that could possibly be a
248 : * member of a MultiXact. Each backend sets its entry to the current
249 : * nextMXact counter just before first acquiring a shared lock in a given
250 : * transaction, and clears it at transaction end. (This works because only
251 : * during or after acquiring a shared lock could an XID possibly become a
252 : * member of a MultiXact, and that MultiXact would have to be created
253 : * during or after the lock acquisition.)
254 : *
255 : * OldestVisibleMXactId[k] is the oldest MultiXactId each backend's
256 : * current transaction(s) think is potentially live, or InvalidMultiXactId
257 : * when not in a transaction or not in a transaction that's paid any
258 : * attention to MultiXacts yet. This is computed when first needed in a
259 : * given transaction, and cleared at transaction end. We can compute it
260 : * as the minimum of the valid OldestMemberMXactId[] entries at the time
261 : * we compute it (using nextMXact if none are valid). Each backend is
262 : * required not to attempt to access any SLRU data for MultiXactIds older
263 : * than its own OldestVisibleMXactId[] setting; this is necessary because
264 : * the checkpointer could truncate away such data at any instant.
265 : *
266 : * The oldest valid value among all of the OldestMemberMXactId[] and
267 : * OldestVisibleMXactId[] entries is considered by vacuum as the earliest
268 : * possible value still having any live member transaction. Subtracting
269 : * vacuum_multixact_freeze_min_age from that value we obtain the freezing
270 : * point for multixacts for that table. Any value older than that is
271 : * removed from tuple headers (or "frozen"; see FreezeMultiXactId. Note
272 : * that multis that have member xids that are older than the cutoff point
273 : * for xids must also be frozen, even if the multis themselves are newer
274 : * than the multixid cutoff point). Whenever a full table vacuum happens,
275 : * the freezing point so computed is used as the new pg_class.relminmxid
276 : * value. The minimum of all those values in a database is stored as
277 : * pg_database.datminmxid. In turn, the minimum of all of those values is
278 : * stored in pg_control and used as truncation point for pg_multixact. At
279 : * checkpoint or restartpoint, unneeded segments are removed.
280 : */
281 : MultiXactId perBackendXactIds[FLEXIBLE_ARRAY_MEMBER];
282 : } MultiXactStateData;
283 :
284 : /*
285 : * Last element of OldestMemberMXactID and OldestVisibleMXactId arrays.
286 : * Valid elements are (1..MaxOldestSlot); element 0 is never used.
287 : */
288 : #define MaxOldestSlot (MaxBackends + max_prepared_xacts)
289 :
290 : /* Pointers to the state data in shared memory */
291 : static MultiXactStateData *MultiXactState;
292 : static MultiXactId *OldestMemberMXactId;
293 : static MultiXactId *OldestVisibleMXactId;
294 :
295 :
296 : /*
297 : * Definitions for the backend-local MultiXactId cache.
298 : *
299 : * We use this cache to store known MultiXacts, so we don't need to go to
300 : * SLRU areas every time.
301 : *
302 : * The cache lasts for the duration of a single transaction, the rationale
303 : * for this being that most entries will contain our own TransactionId and
304 : * so they will be uninteresting by the time our next transaction starts.
305 : * (XXX not clear that this is correct --- other members of the MultiXact
306 : * could hang around longer than we did. However, it's not clear what a
307 : * better policy for flushing old cache entries would be.) FIXME actually
308 : * this is plain wrong now that multixact's may contain update Xids.
309 : *
310 : * We allocate the cache entries in a memory context that is deleted at
311 : * transaction end, so we don't need to do retail freeing of entries.
312 : */
313 : typedef struct mXactCacheEnt
314 : {
315 : MultiXactId multi;
316 : int nmembers;
317 : dlist_node node;
318 : MultiXactMember members[FLEXIBLE_ARRAY_MEMBER];
319 : } mXactCacheEnt;
320 :
321 : #define MAX_CACHE_ENTRIES 256
322 : static dlist_head MXactCache = DLIST_STATIC_INIT(MXactCache);
323 : static int MXactCacheMembers = 0;
324 : static MemoryContext MXactContext = NULL;
325 :
326 : #ifdef MULTIXACT_DEBUG
327 : #define debug_elog2(a,b) elog(a,b)
328 : #define debug_elog3(a,b,c) elog(a,b,c)
329 : #define debug_elog4(a,b,c,d) elog(a,b,c,d)
330 : #define debug_elog5(a,b,c,d,e) elog(a,b,c,d,e)
331 : #define debug_elog6(a,b,c,d,e,f) elog(a,b,c,d,e,f)
332 : #else
333 : #define debug_elog2(a,b)
334 : #define debug_elog3(a,b,c)
335 : #define debug_elog4(a,b,c,d)
336 : #define debug_elog5(a,b,c,d,e)
337 : #define debug_elog6(a,b,c,d,e,f)
338 : #endif
339 :
340 : /* internal MultiXactId management */
341 : static void MultiXactIdSetOldestVisible(void);
342 : static void RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
343 : int nmembers, MultiXactMember *members);
344 : static MultiXactId GetNewMultiXactId(int nmembers, MultiXactOffset *offset);
345 :
346 : /* MultiXact cache management */
347 : static int mxactMemberComparator(const void *arg1, const void *arg2);
348 : static MultiXactId mXactCacheGetBySet(int nmembers, MultiXactMember *members);
349 : static int mXactCacheGetById(MultiXactId multi, MultiXactMember **members);
350 : static void mXactCachePut(MultiXactId multi, int nmembers,
351 : MultiXactMember *members);
352 :
353 : static char *mxstatus_to_string(MultiXactStatus status);
354 :
355 : /* management of SLRU infrastructure */
356 : static int ZeroMultiXactOffsetPage(int pageno, bool writeXlog);
357 : static int ZeroMultiXactMemberPage(int pageno, bool writeXlog);
358 : static bool MultiXactOffsetPagePrecedes(int page1, int page2);
359 : static bool MultiXactMemberPagePrecedes(int page1, int page2);
360 : static bool MultiXactOffsetPrecedes(MultiXactOffset offset1,
361 : MultiXactOffset offset2);
362 : static void ExtendMultiXactOffset(MultiXactId multi);
363 : static void ExtendMultiXactMember(MultiXactOffset offset, int nmembers);
364 : static bool MultiXactOffsetWouldWrap(MultiXactOffset boundary,
365 : MultiXactOffset start, uint32 distance);
366 : static bool SetOffsetVacuumLimit(bool is_startup);
367 : static bool find_multixact_start(MultiXactId multi, MultiXactOffset *result);
368 : static void WriteMZeroPageXlogRec(int pageno, uint8 info);
369 : static void WriteMTruncateXlogRec(Oid oldestMultiDB,
370 : MultiXactId startOff, MultiXactId endOff,
371 : MultiXactOffset startMemb, MultiXactOffset endMemb);
372 :
373 :
374 : /*
375 : * MultiXactIdCreate
376 : * Construct a MultiXactId representing two TransactionIds.
377 : *
378 : * The two XIDs must be different, or be requesting different statuses.
379 : *
380 : * NB - we don't worry about our local MultiXactId cache here, because that
381 : * is handled by the lower-level routines.
382 : */
383 : MultiXactId
384 1 : MultiXactIdCreate(TransactionId xid1, MultiXactStatus status1,
385 : TransactionId xid2, MultiXactStatus status2)
386 : {
387 : MultiXactId newMulti;
388 : MultiXactMember members[2];
389 :
390 1 : AssertArg(TransactionIdIsValid(xid1));
391 1 : AssertArg(TransactionIdIsValid(xid2));
392 :
393 1 : Assert(!TransactionIdEquals(xid1, xid2) || (status1 != status2));
394 :
395 : /* MultiXactIdSetOldestMember() must have been called already. */
396 1 : Assert(MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]));
397 :
398 : /*
399 : * Note: unlike MultiXactIdExpand, we don't bother to check that both XIDs
400 : * are still running. In typical usage, xid2 will be our own XID and the
401 : * caller just did a check on xid1, so it'd be wasted effort.
402 : */
403 :
404 1 : members[0].xid = xid1;
405 1 : members[0].status = status1;
406 1 : members[1].xid = xid2;
407 1 : members[1].status = status2;
408 :
409 1 : newMulti = MultiXactIdCreateFromMembers(2, members);
410 :
411 : debug_elog3(DEBUG2, "Create: %s",
412 : mxid_to_string(newMulti, 2, members));
413 :
414 1 : return newMulti;
415 : }
416 :
417 : /*
418 : * MultiXactIdExpand
419 : * Add a TransactionId to a pre-existing MultiXactId.
420 : *
421 : * If the TransactionId is already a member of the passed MultiXactId with the
422 : * same status, just return it as-is.
423 : *
424 : * Note that we do NOT actually modify the membership of a pre-existing
425 : * MultiXactId; instead we create a new one. This is necessary to avoid
426 : * a race condition against code trying to wait for one MultiXactId to finish;
427 : * see notes in heapam.c.
428 : *
429 : * NB - we don't worry about our local MultiXactId cache here, because that
430 : * is handled by the lower-level routines.
431 : *
432 : * Note: It is critical that MultiXactIds that come from an old cluster (i.e.
433 : * one upgraded by pg_upgrade from a cluster older than this feature) are not
434 : * passed in.
435 : */
436 : MultiXactId
437 1 : MultiXactIdExpand(MultiXactId multi, TransactionId xid, MultiXactStatus status)
438 : {
439 : MultiXactId newMulti;
440 : MultiXactMember *members;
441 : MultiXactMember *newMembers;
442 : int nmembers;
443 : int i;
444 : int j;
445 :
446 1 : AssertArg(MultiXactIdIsValid(multi));
447 1 : AssertArg(TransactionIdIsValid(xid));
448 :
449 : /* MultiXactIdSetOldestMember() must have been called already. */
450 1 : Assert(MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]));
451 :
452 : debug_elog5(DEBUG2, "Expand: received multi %u, xid %u status %s",
453 : multi, xid, mxstatus_to_string(status));
454 :
455 : /*
456 : * Note: we don't allow for old multis here. The reason is that the only
457 : * caller of this function does a check that the multixact is no longer
458 : * running.
459 : */
460 1 : nmembers = GetMultiXactIdMembers(multi, &members, false, false);
461 :
462 1 : if (nmembers < 0)
463 : {
464 : MultiXactMember member;
465 :
466 : /*
467 : * The MultiXactId is obsolete. This can only happen if all the
468 : * MultiXactId members stop running between the caller checking and
469 : * passing it to us. It would be better to return that fact to the
470 : * caller, but it would complicate the API and it's unlikely to happen
471 : * too often, so just deal with it by creating a singleton MultiXact.
472 : */
473 0 : member.xid = xid;
474 0 : member.status = status;
475 0 : newMulti = MultiXactIdCreateFromMembers(1, &member);
476 :
477 : debug_elog4(DEBUG2, "Expand: %u has no members, create singleton %u",
478 : multi, newMulti);
479 0 : return newMulti;
480 : }
481 :
482 : /*
483 : * If the TransactionId is already a member of the MultiXactId with the
484 : * same status, just return the existing MultiXactId.
485 : */
486 3 : for (i = 0; i < nmembers; i++)
487 : {
488 2 : if (TransactionIdEquals(members[i].xid, xid) &&
489 0 : (members[i].status == status))
490 : {
491 : debug_elog4(DEBUG2, "Expand: %u is already a member of %u",
492 : xid, multi);
493 0 : pfree(members);
494 0 : return multi;
495 : }
496 : }
497 :
498 : /*
499 : * Determine which of the members of the MultiXactId are still of
500 : * interest. This is any running transaction, and also any transaction
501 : * that grabbed something stronger than just a lock and was committed. (An
502 : * update that aborted is of no interest here; and having more than one
503 : * update Xid in a multixact would cause errors elsewhere.)
504 : *
505 : * Removing dead members is not just an optimization: freezing of tuples
506 : * whose Xmax are multis depends on this behavior.
507 : *
508 : * Note we have the same race condition here as above: j could be 0 at the
509 : * end of the loop.
510 : */
511 1 : newMembers = (MultiXactMember *)
512 1 : palloc(sizeof(MultiXactMember) * (nmembers + 1));
513 :
514 3 : for (i = 0, j = 0; i < nmembers; i++)
515 : {
516 3 : if (TransactionIdIsInProgress(members[i].xid) ||
517 2 : (ISUPDATE_from_mxstatus(members[i].status) &&
518 1 : TransactionIdDidCommit(members[i].xid)))
519 : {
520 1 : newMembers[j].xid = members[i].xid;
521 1 : newMembers[j++].status = members[i].status;
522 : }
523 : }
524 :
525 1 : newMembers[j].xid = xid;
526 1 : newMembers[j++].status = status;
527 1 : newMulti = MultiXactIdCreateFromMembers(j, newMembers);
528 :
529 1 : pfree(members);
530 1 : pfree(newMembers);
531 :
532 : debug_elog3(DEBUG2, "Expand: returning new multi %u", newMulti);
533 :
534 1 : return newMulti;
535 : }
536 :
537 : /*
538 : * MultiXactIdIsRunning
539 : * Returns whether a MultiXactId is "running".
540 : *
541 : * We return true if at least one member of the given MultiXactId is still
542 : * running. Note that a "false" result is certain not to change,
543 : * because it is not legal to add members to an existing MultiXactId.
544 : *
545 : * Caller is expected to have verified that the multixact does not come from
546 : * a pg_upgraded share-locked tuple.
547 : */
548 : bool
549 2 : MultiXactIdIsRunning(MultiXactId multi, bool isLockOnly)
550 : {
551 : MultiXactMember *members;
552 : int nmembers;
553 : int i;
554 :
555 : debug_elog3(DEBUG2, "IsRunning %u?", multi);
556 :
557 : /*
558 : * "false" here means we assume our callers have checked that the given
559 : * multi cannot possibly come from a pg_upgraded database.
560 : */
561 2 : nmembers = GetMultiXactIdMembers(multi, &members, false, isLockOnly);
562 :
563 2 : if (nmembers <= 0)
564 : {
565 : debug_elog2(DEBUG2, "IsRunning: no members");
566 0 : return false;
567 : }
568 :
569 : /*
570 : * Checking for myself is cheap compared to looking in shared memory;
571 : * return true if any live subtransaction of the current top-level
572 : * transaction is a member.
573 : *
574 : * This is not needed for correctness, it's just a fast path.
575 : */
576 2 : for (i = 0; i < nmembers; i++)
577 : {
578 2 : if (TransactionIdIsCurrentTransactionId(members[i].xid))
579 : {
580 : debug_elog3(DEBUG2, "IsRunning: I (%d) am running!", i);
581 2 : pfree(members);
582 2 : return true;
583 : }
584 : }
585 :
586 : /*
587 : * This could be made faster by having another entry point in procarray.c,
588 : * walking the PGPROC array only once for all the members. But in most
589 : * cases nmembers should be small enough that it doesn't much matter.
590 : */
591 0 : for (i = 0; i < nmembers; i++)
592 : {
593 0 : if (TransactionIdIsInProgress(members[i].xid))
594 : {
595 : debug_elog4(DEBUG2, "IsRunning: member %d (%u) is running",
596 : i, members[i].xid);
597 0 : pfree(members);
598 0 : return true;
599 : }
600 : }
601 :
602 0 : pfree(members);
603 :
604 : debug_elog3(DEBUG2, "IsRunning: %u is not running", multi);
605 :
606 0 : return false;
607 : }
608 :
609 : /*
610 : * MultiXactIdSetOldestMember
611 : * Save the oldest MultiXactId this transaction could be a member of.
612 : *
613 : * We set the OldestMemberMXactId for a given transaction the first time it's
614 : * going to do some operation that might require a MultiXactId (tuple lock,
615 : * update or delete). We need to do this even if we end up using a
616 : * TransactionId instead of a MultiXactId, because there is a chance that
617 : * another transaction would add our XID to a MultiXactId.
618 : *
619 : * The value to set is the next-to-be-assigned MultiXactId, so this is meant to
620 : * be called just before doing any such possibly-MultiXactId-able operation.
621 : */
622 : void
623 118433 : MultiXactIdSetOldestMember(void)
624 : {
625 118433 : if (!MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]))
626 : {
627 : MultiXactId nextMXact;
628 :
629 : /*
630 : * You might think we don't need to acquire a lock here, since
631 : * fetching and storing of TransactionIds is probably atomic, but in
632 : * fact we do: suppose we pick up nextMXact and then lose the CPU for
633 : * a long time. Someone else could advance nextMXact, and then
634 : * another someone else could compute an OldestVisibleMXactId that
635 : * would be after the value we are going to store when we get control
636 : * back. Which would be wrong.
637 : *
638 : * Note that a shared lock is sufficient, because it's enough to stop
639 : * someone from advancing nextMXact; and nobody else could be trying
640 : * to write to our OldestMember entry, only reading (and we assume
641 : * storing it is atomic.)
642 : */
643 5150 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
644 :
645 : /*
646 : * We have to beware of the possibility that nextMXact is in the
647 : * wrapped-around state. We don't fix the counter itself here, but we
648 : * must be sure to store a valid value in our array entry.
649 : */
650 5150 : nextMXact = MultiXactState->nextMXact;
651 5150 : if (nextMXact < FirstMultiXactId)
652 0 : nextMXact = FirstMultiXactId;
653 :
654 5150 : OldestMemberMXactId[MyBackendId] = nextMXact;
655 :
656 5150 : LWLockRelease(MultiXactGenLock);
657 :
658 : debug_elog4(DEBUG2, "MultiXact: setting OldestMember[%d] = %u",
659 : MyBackendId, nextMXact);
660 : }
661 118433 : }
662 :
663 : /*
664 : * MultiXactIdSetOldestVisible
665 : * Save the oldest MultiXactId this transaction considers possibly live.
666 : *
667 : * We set the OldestVisibleMXactId for a given transaction the first time
668 : * it's going to inspect any MultiXactId. Once we have set this, we are
669 : * guaranteed that the checkpointer won't truncate off SLRU data for
670 : * MultiXactIds at or after our OldestVisibleMXactId.
671 : *
672 : * The value to set is the oldest of nextMXact and all the valid per-backend
673 : * OldestMemberMXactId[] entries. Because of the locking we do, we can be
674 : * certain that no subsequent call to MultiXactIdSetOldestMember can set
675 : * an OldestMemberMXactId[] entry older than what we compute here. Therefore
676 : * there is no live transaction, now or later, that can be a member of any
677 : * MultiXactId older than the OldestVisibleMXactId we compute here.
678 : */
679 : static void
680 0 : MultiXactIdSetOldestVisible(void)
681 : {
682 0 : if (!MultiXactIdIsValid(OldestVisibleMXactId[MyBackendId]))
683 : {
684 : MultiXactId oldestMXact;
685 : int i;
686 :
687 0 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
688 :
689 : /*
690 : * We have to beware of the possibility that nextMXact is in the
691 : * wrapped-around state. We don't fix the counter itself here, but we
692 : * must be sure to store a valid value in our array entry.
693 : */
694 0 : oldestMXact = MultiXactState->nextMXact;
695 0 : if (oldestMXact < FirstMultiXactId)
696 0 : oldestMXact = FirstMultiXactId;
697 :
698 0 : for (i = 1; i <= MaxOldestSlot; i++)
699 : {
700 0 : MultiXactId thisoldest = OldestMemberMXactId[i];
701 :
702 0 : if (MultiXactIdIsValid(thisoldest) &&
703 0 : MultiXactIdPrecedes(thisoldest, oldestMXact))
704 0 : oldestMXact = thisoldest;
705 : }
706 :
707 0 : OldestVisibleMXactId[MyBackendId] = oldestMXact;
708 :
709 0 : LWLockRelease(MultiXactGenLock);
710 :
711 : debug_elog4(DEBUG2, "MultiXact: setting OldestVisible[%d] = %u",
712 : MyBackendId, oldestMXact);
713 : }
714 0 : }
715 :
716 : /*
717 : * ReadNextMultiXactId
718 : * Return the next MultiXactId to be assigned, but don't allocate it
719 : */
720 : MultiXactId
721 1219 : ReadNextMultiXactId(void)
722 : {
723 : MultiXactId mxid;
724 :
725 : /* XXX we could presumably do this without a lock. */
726 1219 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
727 1219 : mxid = MultiXactState->nextMXact;
728 1219 : LWLockRelease(MultiXactGenLock);
729 :
730 1219 : if (mxid < FirstMultiXactId)
731 0 : mxid = FirstMultiXactId;
732 :
733 1219 : return mxid;
734 : }
735 :
736 : /*
737 : * MultiXactIdCreateFromMembers
738 : * Make a new MultiXactId from the specified set of members
739 : *
740 : * Make XLOG, SLRU and cache entries for a new MultiXactId, recording the
741 : * given TransactionIds as members. Returns the newly created MultiXactId.
742 : *
743 : * NB: the passed members[] array will be sorted in-place.
744 : */
745 : MultiXactId
746 2 : MultiXactIdCreateFromMembers(int nmembers, MultiXactMember *members)
747 : {
748 : MultiXactId multi;
749 : MultiXactOffset offset;
750 : xl_multixact_create xlrec;
751 :
752 : debug_elog3(DEBUG2, "Create: %s",
753 : mxid_to_string(InvalidMultiXactId, nmembers, members));
754 :
755 : /*
756 : * See if the same set of members already exists in our cache; if so, just
757 : * re-use that MultiXactId. (Note: it might seem that looking in our
758 : * cache is insufficient, and we ought to search disk to see if a
759 : * duplicate definition already exists. But since we only ever create
760 : * MultiXacts containing our own XID, in most cases any such MultiXacts
761 : * were in fact created by us, and so will be in our cache. There are
762 : * corner cases where someone else added us to a MultiXact without our
763 : * knowledge, but it's not worth checking for.)
764 : */
765 2 : multi = mXactCacheGetBySet(nmembers, members);
766 2 : if (MultiXactIdIsValid(multi))
767 : {
768 : debug_elog2(DEBUG2, "Create: in cache!");
769 0 : return multi;
770 : }
771 :
772 : /* Verify that there is a single update Xid among the given members. */
773 : {
774 : int i;
775 2 : bool has_update = false;
776 :
777 6 : for (i = 0; i < nmembers; i++)
778 : {
779 4 : if (ISUPDATE_from_mxstatus(members[i].status))
780 : {
781 1 : if (has_update)
782 0 : elog(ERROR, "new multixact has more than one updating member");
783 1 : has_update = true;
784 : }
785 : }
786 : }
787 :
788 : /*
789 : * Assign the MXID and offsets range to use, and make sure there is space
790 : * in the OFFSETs and MEMBERs files. NB: this routine does
791 : * START_CRIT_SECTION().
792 : *
793 : * Note: unlike MultiXactIdCreate and MultiXactIdExpand, we do not check
794 : * that we've called MultiXactIdSetOldestMember here. This is because
795 : * this routine is used in some places to create new MultiXactIds of which
796 : * the current backend is not a member, notably during freezing of multis
797 : * in vacuum. During vacuum, in particular, it would be unacceptable to
798 : * keep OldestMulti set, in case it runs for long.
799 : */
800 2 : multi = GetNewMultiXactId(nmembers, &offset);
801 :
802 : /* Make an XLOG entry describing the new MXID. */
803 2 : xlrec.mid = multi;
804 2 : xlrec.moff = offset;
805 2 : xlrec.nmembers = nmembers;
806 :
807 : /*
808 : * XXX Note: there's a lot of padding space in MultiXactMember. We could
809 : * find a more compact representation of this Xlog record -- perhaps all
810 : * the status flags in one XLogRecData, then all the xids in another one?
811 : * Not clear that it's worth the trouble though.
812 : */
813 2 : XLogBeginInsert();
814 2 : XLogRegisterData((char *) (&xlrec), SizeOfMultiXactCreate);
815 2 : XLogRegisterData((char *) members, nmembers * sizeof(MultiXactMember));
816 :
817 2 : (void) XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_CREATE_ID);
818 :
819 : /* Now enter the information into the OFFSETs and MEMBERs logs */
820 2 : RecordNewMultiXact(multi, offset, nmembers, members);
821 :
822 : /* Done with critical section */
823 2 : END_CRIT_SECTION();
824 :
825 : /* Store the new MultiXactId in the local cache, too */
826 2 : mXactCachePut(multi, nmembers, members);
827 :
828 : debug_elog2(DEBUG2, "Create: all done");
829 :
830 2 : return multi;
831 : }
832 :
833 : /*
834 : * RecordNewMultiXact
835 : * Write info about a new multixact into the offsets and members files
836 : *
837 : * This is broken out of MultiXactIdCreateFromMembers so that xlog replay can
838 : * use it.
839 : */
840 : static void
841 2 : RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
842 : int nmembers, MultiXactMember *members)
843 : {
844 : int pageno;
845 : int prev_pageno;
846 : int entryno;
847 : int slotno;
848 : MultiXactOffset *offptr;
849 : int i;
850 :
851 2 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
852 :
853 2 : pageno = MultiXactIdToOffsetPage(multi);
854 2 : entryno = MultiXactIdToOffsetEntry(multi);
855 :
856 : /*
857 : * Note: we pass the MultiXactId to SimpleLruReadPage as the "transaction"
858 : * to complain about if there's any I/O error. This is kinda bogus, but
859 : * since the errors will always give the full pathname, it should be clear
860 : * enough that a MultiXactId is really involved. Perhaps someday we'll
861 : * take the trouble to generalize the slru.c error reporting code.
862 : */
863 2 : slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
864 2 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
865 2 : offptr += entryno;
866 :
867 2 : *offptr = offset;
868 :
869 2 : MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
870 :
871 : /* Exchange our lock */
872 2 : LWLockRelease(MultiXactOffsetControlLock);
873 :
874 2 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
875 :
876 2 : prev_pageno = -1;
877 :
878 6 : for (i = 0; i < nmembers; i++, offset++)
879 : {
880 : TransactionId *memberptr;
881 : uint32 *flagsptr;
882 : uint32 flagsval;
883 : int bshift;
884 : int flagsoff;
885 : int memberoff;
886 :
887 4 : Assert(members[i].status <= MultiXactStatusUpdate);
888 :
889 4 : pageno = MXOffsetToMemberPage(offset);
890 4 : memberoff = MXOffsetToMemberOffset(offset);
891 4 : flagsoff = MXOffsetToFlagsOffset(offset);
892 4 : bshift = MXOffsetToFlagsBitShift(offset);
893 :
894 4 : if (pageno != prev_pageno)
895 : {
896 2 : slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
897 2 : prev_pageno = pageno;
898 : }
899 :
900 4 : memberptr = (TransactionId *)
901 4 : (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
902 :
903 4 : *memberptr = members[i].xid;
904 :
905 4 : flagsptr = (uint32 *)
906 4 : (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
907 :
908 4 : flagsval = *flagsptr;
909 4 : flagsval &= ~(((1 << MXACT_MEMBER_BITS_PER_XACT) - 1) << bshift);
910 4 : flagsval |= (members[i].status << bshift);
911 4 : *flagsptr = flagsval;
912 :
913 4 : MultiXactMemberCtl->shared->page_dirty[slotno] = true;
914 : }
915 :
916 2 : LWLockRelease(MultiXactMemberControlLock);
917 2 : }
918 :
919 : /*
920 : * GetNewMultiXactId
921 : * Get the next MultiXactId.
922 : *
923 : * Also, reserve the needed amount of space in the "members" area. The
924 : * starting offset of the reserved space is returned in *offset.
925 : *
926 : * This may generate XLOG records for expansion of the offsets and/or members
927 : * files. Unfortunately, we have to do that while holding MultiXactGenLock
928 : * to avoid race conditions --- the XLOG record for zeroing a page must appear
929 : * before any backend can possibly try to store data in that page!
930 : *
931 : * We start a critical section before advancing the shared counters. The
932 : * caller must end the critical section after writing SLRU data.
933 : */
934 : static MultiXactId
935 2 : GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
936 : {
937 : MultiXactId result;
938 : MultiXactOffset nextOffset;
939 :
940 : debug_elog3(DEBUG2, "GetNew: for %d xids", nmembers);
941 :
942 : /* safety check, we should never get this far in a HS standby */
943 2 : if (RecoveryInProgress())
944 0 : elog(ERROR, "cannot assign MultiXactIds during recovery");
945 :
946 2 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
947 :
948 : /* Handle wraparound of the nextMXact counter */
949 2 : if (MultiXactState->nextMXact < FirstMultiXactId)
950 0 : MultiXactState->nextMXact = FirstMultiXactId;
951 :
952 : /* Assign the MXID */
953 2 : result = MultiXactState->nextMXact;
954 :
955 : /*----------
956 : * Check to see if it's safe to assign another MultiXactId. This protects
957 : * against catastrophic data loss due to multixact wraparound. The basic
958 : * rules are:
959 : *
960 : * If we're past multiVacLimit or the safe threshold for member storage
961 : * space, or we don't know what the safe threshold for member storage is,
962 : * start trying to force autovacuum cycles.
963 : * If we're past multiWarnLimit, start issuing warnings.
964 : * If we're past multiStopLimit, refuse to create new MultiXactIds.
965 : *
966 : * Note these are pretty much the same protections in GetNewTransactionId.
967 : *----------
968 : */
969 2 : if (!MultiXactIdPrecedes(result, MultiXactState->multiVacLimit))
970 : {
971 : /*
972 : * For safety's sake, we release MultiXactGenLock while sending
973 : * signals, warnings, etc. This is not so much because we care about
974 : * preserving concurrency in this situation, as to avoid any
975 : * possibility of deadlock while doing get_database_name(). First,
976 : * copy all the shared values we'll need in this path.
977 : */
978 0 : MultiXactId multiWarnLimit = MultiXactState->multiWarnLimit;
979 0 : MultiXactId multiStopLimit = MultiXactState->multiStopLimit;
980 0 : MultiXactId multiWrapLimit = MultiXactState->multiWrapLimit;
981 0 : Oid oldest_datoid = MultiXactState->oldestMultiXactDB;
982 :
983 0 : LWLockRelease(MultiXactGenLock);
984 :
985 0 : if (IsUnderPostmaster &&
986 0 : !MultiXactIdPrecedes(result, multiStopLimit))
987 : {
988 0 : char *oldest_datname = get_database_name(oldest_datoid);
989 :
990 : /*
991 : * Immediately kick autovacuum into action as we're already in
992 : * ERROR territory.
993 : */
994 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
995 :
996 : /* complain even if that DB has disappeared */
997 0 : if (oldest_datname)
998 0 : ereport(ERROR,
999 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1000 : errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database \"%s\"",
1001 : oldest_datname),
1002 : errhint("Execute a database-wide VACUUM in that database.\n"
1003 : "You might also need to commit or roll back old prepared transactions.")));
1004 : else
1005 0 : ereport(ERROR,
1006 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1007 : errmsg("database is not accepting commands that generate new MultiXactIds to avoid wraparound data loss in database with OID %u",
1008 : oldest_datoid),
1009 : errhint("Execute a database-wide VACUUM in that database.\n"
1010 : "You might also need to commit or roll back old prepared transactions.")));
1011 : }
1012 :
1013 : /*
1014 : * To avoid swamping the postmaster with signals, we issue the autovac
1015 : * request only once per 64K multis generated. This still gives
1016 : * plenty of chances before we get into real trouble.
1017 : */
1018 0 : if (IsUnderPostmaster && (result % 65536) == 0)
1019 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
1020 :
1021 0 : if (!MultiXactIdPrecedes(result, multiWarnLimit))
1022 : {
1023 0 : char *oldest_datname = get_database_name(oldest_datoid);
1024 :
1025 : /* complain even if that DB has disappeared */
1026 0 : if (oldest_datname)
1027 0 : ereport(WARNING,
1028 : (errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
1029 : "database \"%s\" must be vacuumed before %u more MultiXactIds are used",
1030 : multiWrapLimit - result,
1031 : oldest_datname,
1032 : multiWrapLimit - result),
1033 : errhint("Execute a database-wide VACUUM in that database.\n"
1034 : "You might also need to commit or roll back old prepared transactions.")));
1035 : else
1036 0 : ereport(WARNING,
1037 : (errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
1038 : "database with OID %u must be vacuumed before %u more MultiXactIds are used",
1039 : multiWrapLimit - result,
1040 : oldest_datoid,
1041 : multiWrapLimit - result),
1042 : errhint("Execute a database-wide VACUUM in that database.\n"
1043 : "You might also need to commit or roll back old prepared transactions.")));
1044 : }
1045 :
1046 : /* Re-acquire lock and start over */
1047 0 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
1048 0 : result = MultiXactState->nextMXact;
1049 0 : if (result < FirstMultiXactId)
1050 0 : result = FirstMultiXactId;
1051 : }
1052 :
1053 : /* Make sure there is room for the MXID in the file. */
1054 2 : ExtendMultiXactOffset(result);
1055 :
1056 : /*
1057 : * Reserve the members space, similarly to above. Also, be careful not to
1058 : * return zero as the starting offset for any multixact. See
1059 : * GetMultiXactIdMembers() for motivation.
1060 : */
1061 2 : nextOffset = MultiXactState->nextOffset;
1062 2 : if (nextOffset == 0)
1063 : {
1064 1 : *offset = 1;
1065 1 : nmembers++; /* allocate member slot 0 too */
1066 : }
1067 : else
1068 1 : *offset = nextOffset;
1069 :
1070 : /*----------
1071 : * Protect against overrun of the members space as well, with the
1072 : * following rules:
1073 : *
1074 : * If we're past offsetStopLimit, refuse to generate more multis.
1075 : * If we're close to offsetStopLimit, emit a warning.
1076 : *
1077 : * Arbitrarily, we start emitting warnings when we're 20 segments or less
1078 : * from offsetStopLimit.
1079 : *
1080 : * Note we haven't updated the shared state yet, so if we fail at this
1081 : * point, the multixact ID we grabbed can still be used by the next guy.
1082 : *
1083 : * Note that there is no point in forcing autovacuum runs here: the
1084 : * multixact freeze settings would have to be reduced for that to have any
1085 : * effect.
1086 : *----------
1087 : */
1088 : #define OFFSET_WARN_SEGMENTS 20
1089 4 : if (MultiXactState->oldestOffsetKnown &&
1090 2 : MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit, nextOffset,
1091 : nmembers))
1092 : {
1093 : /* see comment in the corresponding offsets wraparound case */
1094 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
1095 :
1096 0 : ereport(ERROR,
1097 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1098 : errmsg("multixact \"members\" limit exceeded"),
1099 : errdetail_plural("This command would create a multixact with %u members, but the remaining space is only enough for %u member.",
1100 : "This command would create a multixact with %u members, but the remaining space is only enough for %u members.",
1101 : MultiXactState->offsetStopLimit - nextOffset - 1,
1102 : nmembers,
1103 : MultiXactState->offsetStopLimit - nextOffset - 1),
1104 : errhint("Execute a database-wide VACUUM in database with OID %u with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.",
1105 : MultiXactState->oldestMultiXactDB)));
1106 : }
1107 :
1108 : /*
1109 : * Check whether we should kick autovacuum into action, to prevent members
1110 : * wraparound. NB we use a much larger window to trigger autovacuum than
1111 : * just the warning limit. The warning is just a measure of last resort -
1112 : * this is in line with GetNewTransactionId's behaviour.
1113 : */
1114 4 : if (!MultiXactState->oldestOffsetKnown ||
1115 2 : (MultiXactState->nextOffset - MultiXactState->oldestOffset
1116 2 : > MULTIXACT_MEMBER_SAFE_THRESHOLD))
1117 : {
1118 : /*
1119 : * To avoid swamping the postmaster with signals, we issue the autovac
1120 : * request only when crossing a segment boundary. With default
1121 : * compilation settings that's roughly after 50k members. This still
1122 : * gives plenty of chances before we get into real trouble.
1123 : */
1124 0 : if ((MXOffsetToMemberPage(nextOffset) / SLRU_PAGES_PER_SEGMENT) !=
1125 0 : (MXOffsetToMemberPage(nextOffset + nmembers) / SLRU_PAGES_PER_SEGMENT))
1126 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
1127 : }
1128 :
1129 4 : if (MultiXactState->oldestOffsetKnown &&
1130 2 : MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit,
1131 : nextOffset,
1132 : nmembers + MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT * OFFSET_WARN_SEGMENTS))
1133 0 : ereport(WARNING,
1134 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1135 : errmsg_plural("database with OID %u must be vacuumed before %d more multixact member is used",
1136 : "database with OID %u must be vacuumed before %d more multixact members are used",
1137 : MultiXactState->offsetStopLimit - nextOffset + nmembers,
1138 : MultiXactState->oldestMultiXactDB,
1139 : MultiXactState->offsetStopLimit - nextOffset + nmembers),
1140 : errhint("Execute a database-wide VACUUM in that database with reduced vacuum_multixact_freeze_min_age and vacuum_multixact_freeze_table_age settings.")));
1141 :
1142 2 : ExtendMultiXactMember(nextOffset, nmembers);
1143 :
1144 : /*
1145 : * Critical section from here until caller has written the data into the
1146 : * just-reserved SLRU space; we don't want to error out with a partly
1147 : * written MultiXact structure. (In particular, failing to write our
1148 : * start offset after advancing nextMXact would effectively corrupt the
1149 : * previous MultiXact.)
1150 : */
1151 2 : START_CRIT_SECTION();
1152 :
1153 : /*
1154 : * Advance counters. As in GetNewTransactionId(), this must not happen
1155 : * until after file extension has succeeded!
1156 : *
1157 : * We don't care about MultiXactId wraparound here; it will be handled by
1158 : * the next iteration. But note that nextMXact may be InvalidMultiXactId
1159 : * or the first value on a segment-beginning page after this routine
1160 : * exits, so anyone else looking at the variable must be prepared to deal
1161 : * with either case. Similarly, nextOffset may be zero, but we won't use
1162 : * that as the actual start offset of the next multixact.
1163 : */
1164 2 : (MultiXactState->nextMXact)++;
1165 :
1166 2 : MultiXactState->nextOffset += nmembers;
1167 :
1168 2 : LWLockRelease(MultiXactGenLock);
1169 :
1170 : debug_elog4(DEBUG2, "GetNew: returning %u offset %u", result, *offset);
1171 2 : return result;
1172 : }
1173 :
1174 : /*
1175 : * GetMultiXactIdMembers
1176 : * Return the set of MultiXactMembers that make up a MultiXactId
1177 : *
1178 : * Return value is the number of members found, or -1 if there are none,
1179 : * and *members is set to a newly palloc'ed array of members. It's the
1180 : * caller's responsibility to free it when done with it.
1181 : *
1182 : * from_pgupgrade must be passed as true if and only if only the multixact
1183 : * corresponds to a value from a tuple that was locked in a 9.2-or-older
1184 : * installation and later pg_upgrade'd (that is, the infomask is
1185 : * HEAP_LOCKED_UPGRADED). In this case, we know for certain that no members
1186 : * can still be running, so we return -1 just like for an empty multixact
1187 : * without any further checking. It would be wrong to try to resolve such a
1188 : * multixact: either the multixact is within the current valid multixact
1189 : * range, in which case the returned result would be bogus, or outside that
1190 : * range, in which case an error would be raised.
1191 : *
1192 : * In all other cases, the passed multixact must be within the known valid
1193 : * range, that is, greater to or equal than oldestMultiXactId, and less than
1194 : * nextMXact. Otherwise, an error is raised.
1195 : *
1196 : * onlyLock must be set to true if caller is certain that the given multi
1197 : * is used only to lock tuples; can be false without loss of correctness,
1198 : * but passing a true means we can return quickly without checking for
1199 : * old updates.
1200 : */
1201 : int
1202 10 : GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,
1203 : bool from_pgupgrade, bool onlyLock)
1204 : {
1205 : int pageno;
1206 : int prev_pageno;
1207 : int entryno;
1208 : int slotno;
1209 : MultiXactOffset *offptr;
1210 : MultiXactOffset offset;
1211 : int length;
1212 : int truelength;
1213 : int i;
1214 : MultiXactId oldestMXact;
1215 : MultiXactId nextMXact;
1216 : MultiXactId tmpMXact;
1217 : MultiXactOffset nextOffset;
1218 : MultiXactMember *ptr;
1219 :
1220 : debug_elog3(DEBUG2, "GetMembers: asked for %u", multi);
1221 :
1222 10 : if (!MultiXactIdIsValid(multi) || from_pgupgrade)
1223 0 : return -1;
1224 :
1225 : /* See if the MultiXactId is in the local cache */
1226 10 : length = mXactCacheGetById(multi, members);
1227 10 : if (length >= 0)
1228 : {
1229 : debug_elog3(DEBUG2, "GetMembers: found %s in the cache",
1230 : mxid_to_string(multi, length, *members));
1231 10 : return length;
1232 : }
1233 :
1234 : /* Set our OldestVisibleMXactId[] entry if we didn't already */
1235 0 : MultiXactIdSetOldestVisible();
1236 :
1237 : /*
1238 : * If we know the multi is used only for locking and not for updates, then
1239 : * we can skip checking if the value is older than our oldest visible
1240 : * multi. It cannot possibly still be running.
1241 : */
1242 0 : if (onlyLock &&
1243 0 : MultiXactIdPrecedes(multi, OldestVisibleMXactId[MyBackendId]))
1244 : {
1245 : debug_elog2(DEBUG2, "GetMembers: a locker-only multi is too old");
1246 0 : *members = NULL;
1247 0 : return -1;
1248 : }
1249 :
1250 : /*
1251 : * We check known limits on MultiXact before resorting to the SLRU area.
1252 : *
1253 : * An ID older than MultiXactState->oldestMultiXactId cannot possibly be
1254 : * useful; it has already been removed, or will be removed shortly, by
1255 : * truncation. If one is passed, an error is raised.
1256 : *
1257 : * Also, an ID >= nextMXact shouldn't ever be seen here; if it is seen, it
1258 : * implies undetected ID wraparound has occurred. This raises a hard
1259 : * error.
1260 : *
1261 : * Shared lock is enough here since we aren't modifying any global state.
1262 : * Acquire it just long enough to grab the current counter values. We may
1263 : * need both nextMXact and nextOffset; see below.
1264 : */
1265 0 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
1266 :
1267 0 : oldestMXact = MultiXactState->oldestMultiXactId;
1268 0 : nextMXact = MultiXactState->nextMXact;
1269 0 : nextOffset = MultiXactState->nextOffset;
1270 :
1271 0 : LWLockRelease(MultiXactGenLock);
1272 :
1273 0 : if (MultiXactIdPrecedes(multi, oldestMXact))
1274 : {
1275 0 : ereport(ERROR,
1276 : (errcode(ERRCODE_INTERNAL_ERROR),
1277 : errmsg("MultiXactId %u does no longer exist -- apparent wraparound",
1278 : multi)));
1279 : return -1;
1280 : }
1281 :
1282 0 : if (!MultiXactIdPrecedes(multi, nextMXact))
1283 0 : ereport(ERROR,
1284 : (errcode(ERRCODE_INTERNAL_ERROR),
1285 : errmsg("MultiXactId %u has not been created yet -- apparent wraparound",
1286 : multi)));
1287 :
1288 : /*
1289 : * Find out the offset at which we need to start reading MultiXactMembers
1290 : * and the number of members in the multixact. We determine the latter as
1291 : * the difference between this multixact's starting offset and the next
1292 : * one's. However, there are some corner cases to worry about:
1293 : *
1294 : * 1. This multixact may be the latest one created, in which case there is
1295 : * no next one to look at. In this case the nextOffset value we just
1296 : * saved is the correct endpoint.
1297 : *
1298 : * 2. The next multixact may still be in process of being filled in: that
1299 : * is, another process may have done GetNewMultiXactId but not yet written
1300 : * the offset entry for that ID. In that scenario, it is guaranteed that
1301 : * the offset entry for that multixact exists (because GetNewMultiXactId
1302 : * won't release MultiXactGenLock until it does) but contains zero
1303 : * (because we are careful to pre-zero offset pages). Because
1304 : * GetNewMultiXactId will never return zero as the starting offset for a
1305 : * multixact, when we read zero as the next multixact's offset, we know we
1306 : * have this case. We sleep for a bit and try again.
1307 : *
1308 : * 3. Because GetNewMultiXactId increments offset zero to offset one to
1309 : * handle case #2, there is an ambiguity near the point of offset
1310 : * wraparound. If we see next multixact's offset is one, is that our
1311 : * multixact's actual endpoint, or did it end at zero with a subsequent
1312 : * increment? We handle this using the knowledge that if the zero'th
1313 : * member slot wasn't filled, it'll contain zero, and zero isn't a valid
1314 : * transaction ID so it can't be a multixact member. Therefore, if we
1315 : * read a zero from the members array, just ignore it.
1316 : *
1317 : * This is all pretty messy, but the mess occurs only in infrequent corner
1318 : * cases, so it seems better than holding the MultiXactGenLock for a long
1319 : * time on every multixact creation.
1320 : */
1321 : retry:
1322 0 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1323 :
1324 0 : pageno = MultiXactIdToOffsetPage(multi);
1325 0 : entryno = MultiXactIdToOffsetEntry(multi);
1326 :
1327 0 : slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi);
1328 0 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
1329 0 : offptr += entryno;
1330 0 : offset = *offptr;
1331 :
1332 0 : Assert(offset != 0);
1333 :
1334 : /*
1335 : * Use the same increment rule as GetNewMultiXactId(), that is, don't
1336 : * handle wraparound explicitly until needed.
1337 : */
1338 0 : tmpMXact = multi + 1;
1339 :
1340 0 : if (nextMXact == tmpMXact)
1341 : {
1342 : /* Corner case 1: there is no next multixact */
1343 0 : length = nextOffset - offset;
1344 : }
1345 : else
1346 : {
1347 : MultiXactOffset nextMXOffset;
1348 :
1349 : /* handle wraparound if needed */
1350 0 : if (tmpMXact < FirstMultiXactId)
1351 0 : tmpMXact = FirstMultiXactId;
1352 :
1353 0 : prev_pageno = pageno;
1354 :
1355 0 : pageno = MultiXactIdToOffsetPage(tmpMXact);
1356 0 : entryno = MultiXactIdToOffsetEntry(tmpMXact);
1357 :
1358 0 : if (pageno != prev_pageno)
1359 0 : slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, tmpMXact);
1360 :
1361 0 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
1362 0 : offptr += entryno;
1363 0 : nextMXOffset = *offptr;
1364 :
1365 0 : if (nextMXOffset == 0)
1366 : {
1367 : /* Corner case 2: next multixact is still being filled in */
1368 0 : LWLockRelease(MultiXactOffsetControlLock);
1369 0 : CHECK_FOR_INTERRUPTS();
1370 0 : pg_usleep(1000L);
1371 0 : goto retry;
1372 : }
1373 :
1374 0 : length = nextMXOffset - offset;
1375 : }
1376 :
1377 0 : LWLockRelease(MultiXactOffsetControlLock);
1378 :
1379 0 : ptr = (MultiXactMember *) palloc(length * sizeof(MultiXactMember));
1380 0 : *members = ptr;
1381 :
1382 : /* Now get the members themselves. */
1383 0 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
1384 :
1385 0 : truelength = 0;
1386 0 : prev_pageno = -1;
1387 0 : for (i = 0; i < length; i++, offset++)
1388 : {
1389 : TransactionId *xactptr;
1390 : uint32 *flagsptr;
1391 : int flagsoff;
1392 : int bshift;
1393 : int memberoff;
1394 :
1395 0 : pageno = MXOffsetToMemberPage(offset);
1396 0 : memberoff = MXOffsetToMemberOffset(offset);
1397 :
1398 0 : if (pageno != prev_pageno)
1399 : {
1400 0 : slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi);
1401 0 : prev_pageno = pageno;
1402 : }
1403 :
1404 0 : xactptr = (TransactionId *)
1405 0 : (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
1406 :
1407 0 : if (!TransactionIdIsValid(*xactptr))
1408 : {
1409 : /* Corner case 3: we must be looking at unused slot zero */
1410 0 : Assert(offset == 0);
1411 0 : continue;
1412 : }
1413 :
1414 0 : flagsoff = MXOffsetToFlagsOffset(offset);
1415 0 : bshift = MXOffsetToFlagsBitShift(offset);
1416 0 : flagsptr = (uint32 *) (MultiXactMemberCtl->shared->page_buffer[slotno] + flagsoff);
1417 :
1418 0 : ptr[truelength].xid = *xactptr;
1419 0 : ptr[truelength].status = (*flagsptr >> bshift) & MXACT_MEMBER_XACT_BITMASK;
1420 0 : truelength++;
1421 : }
1422 :
1423 0 : LWLockRelease(MultiXactMemberControlLock);
1424 :
1425 : /*
1426 : * Copy the result into the local cache.
1427 : */
1428 0 : mXactCachePut(multi, truelength, ptr);
1429 :
1430 : debug_elog3(DEBUG2, "GetMembers: no cache for %s",
1431 : mxid_to_string(multi, truelength, ptr));
1432 0 : return truelength;
1433 : }
1434 :
1435 : /*
1436 : * mxactMemberComparator
1437 : * qsort comparison function for MultiXactMember
1438 : *
1439 : * We can't use wraparound comparison for XIDs because that does not respect
1440 : * the triangle inequality! Any old sort order will do.
1441 : */
1442 : static int
1443 4 : mxactMemberComparator(const void *arg1, const void *arg2)
1444 : {
1445 4 : MultiXactMember member1 = *(const MultiXactMember *) arg1;
1446 4 : MultiXactMember member2 = *(const MultiXactMember *) arg2;
1447 :
1448 4 : if (member1.xid > member2.xid)
1449 0 : return 1;
1450 4 : if (member1.xid < member2.xid)
1451 4 : return -1;
1452 0 : if (member1.status > member2.status)
1453 0 : return 1;
1454 0 : if (member1.status < member2.status)
1455 0 : return -1;
1456 0 : return 0;
1457 : }
1458 :
1459 : /*
1460 : * mXactCacheGetBySet
1461 : * returns a MultiXactId from the cache based on the set of
1462 : * TransactionIds that compose it, or InvalidMultiXactId if
1463 : * none matches.
1464 : *
1465 : * This is helpful, for example, if two transactions want to lock a huge
1466 : * table. By using the cache, the second will use the same MultiXactId
1467 : * for the majority of tuples, thus keeping MultiXactId usage low (saving
1468 : * both I/O and wraparound issues).
1469 : *
1470 : * NB: the passed members array will be sorted in-place.
1471 : */
1472 : static MultiXactId
1473 2 : mXactCacheGetBySet(int nmembers, MultiXactMember *members)
1474 : {
1475 : dlist_iter iter;
1476 :
1477 : debug_elog3(DEBUG2, "CacheGet: looking for %s",
1478 : mxid_to_string(InvalidMultiXactId, nmembers, members));
1479 :
1480 : /* sort the array so comparison is easy */
1481 2 : qsort(members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
1482 :
1483 3 : dlist_foreach(iter, &MXactCache)
1484 : {
1485 1 : mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
1486 :
1487 1 : if (entry->nmembers != nmembers)
1488 0 : continue;
1489 :
1490 : /*
1491 : * We assume the cache entries are sorted, and that the unused bits in
1492 : * "status" are zeroed.
1493 : */
1494 1 : if (memcmp(members, entry->members, nmembers * sizeof(MultiXactMember)) == 0)
1495 : {
1496 : debug_elog3(DEBUG2, "CacheGet: found %u", entry->multi);
1497 0 : dlist_move_head(&MXactCache, iter.cur);
1498 0 : return entry->multi;
1499 : }
1500 : }
1501 :
1502 : debug_elog2(DEBUG2, "CacheGet: not found :-(");
1503 2 : return InvalidMultiXactId;
1504 : }
1505 :
1506 : /*
1507 : * mXactCacheGetById
1508 : * returns the composing MultiXactMember set from the cache for a
1509 : * given MultiXactId, if present.
1510 : *
1511 : * If successful, *xids is set to the address of a palloc'd copy of the
1512 : * MultiXactMember set. Return value is number of members, or -1 on failure.
1513 : */
1514 : static int
1515 10 : mXactCacheGetById(MultiXactId multi, MultiXactMember **members)
1516 : {
1517 : dlist_iter iter;
1518 :
1519 : debug_elog3(DEBUG2, "CacheGet: looking for %u", multi);
1520 :
1521 10 : dlist_foreach(iter, &MXactCache)
1522 : {
1523 10 : mXactCacheEnt *entry = dlist_container(mXactCacheEnt, node, iter.cur);
1524 :
1525 10 : if (entry->multi == multi)
1526 : {
1527 : MultiXactMember *ptr;
1528 : Size size;
1529 :
1530 10 : size = sizeof(MultiXactMember) * entry->nmembers;
1531 10 : ptr = (MultiXactMember *) palloc(size);
1532 10 : *members = ptr;
1533 :
1534 10 : memcpy(ptr, entry->members, size);
1535 :
1536 : debug_elog3(DEBUG2, "CacheGet: found %s",
1537 : mxid_to_string(multi,
1538 : entry->nmembers,
1539 : entry->members));
1540 :
1541 : /*
1542 : * Note we modify the list while not using a modifiable iterator.
1543 : * This is acceptable only because we exit the iteration
1544 : * immediately afterwards.
1545 : */
1546 10 : dlist_move_head(&MXactCache, iter.cur);
1547 :
1548 10 : return entry->nmembers;
1549 : }
1550 : }
1551 :
1552 : debug_elog2(DEBUG2, "CacheGet: not found");
1553 0 : return -1;
1554 : }
1555 :
1556 : /*
1557 : * mXactCachePut
1558 : * Add a new MultiXactId and its composing set into the local cache.
1559 : */
1560 : static void
1561 2 : mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
1562 : {
1563 : mXactCacheEnt *entry;
1564 :
1565 : debug_elog3(DEBUG2, "CachePut: storing %s",
1566 : mxid_to_string(multi, nmembers, members));
1567 :
1568 2 : if (MXactContext == NULL)
1569 : {
1570 : /* The cache only lives as long as the current transaction */
1571 : debug_elog2(DEBUG2, "CachePut: initializing memory context");
1572 1 : MXactContext = AllocSetContextCreate(TopTransactionContext,
1573 : "MultiXact cache context",
1574 : ALLOCSET_SMALL_SIZES);
1575 : }
1576 :
1577 2 : entry = (mXactCacheEnt *)
1578 2 : MemoryContextAlloc(MXactContext,
1579 : offsetof(mXactCacheEnt, members) +
1580 : nmembers * sizeof(MultiXactMember));
1581 :
1582 2 : entry->multi = multi;
1583 2 : entry->nmembers = nmembers;
1584 2 : memcpy(entry->members, members, nmembers * sizeof(MultiXactMember));
1585 :
1586 : /* mXactCacheGetBySet assumes the entries are sorted, so sort them */
1587 2 : qsort(entry->members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
1588 :
1589 2 : dlist_push_head(&MXactCache, &entry->node);
1590 2 : if (MXactCacheMembers++ >= MAX_CACHE_ENTRIES)
1591 : {
1592 : dlist_node *node;
1593 : mXactCacheEnt *entry;
1594 :
1595 0 : node = dlist_tail_node(&MXactCache);
1596 0 : dlist_delete(node);
1597 0 : MXactCacheMembers--;
1598 :
1599 0 : entry = dlist_container(mXactCacheEnt, node, node);
1600 : debug_elog3(DEBUG2, "CachePut: pruning cached multi %u",
1601 : entry->multi);
1602 :
1603 0 : pfree(entry);
1604 : }
1605 2 : }
1606 :
1607 : static char *
1608 0 : mxstatus_to_string(MultiXactStatus status)
1609 : {
1610 0 : switch (status)
1611 : {
1612 : case MultiXactStatusForKeyShare:
1613 0 : return "keysh";
1614 : case MultiXactStatusForShare:
1615 0 : return "sh";
1616 : case MultiXactStatusForNoKeyUpdate:
1617 0 : return "fornokeyupd";
1618 : case MultiXactStatusForUpdate:
1619 0 : return "forupd";
1620 : case MultiXactStatusNoKeyUpdate:
1621 0 : return "nokeyupd";
1622 : case MultiXactStatusUpdate:
1623 0 : return "upd";
1624 : default:
1625 0 : elog(ERROR, "unrecognized multixact status %d", status);
1626 : return "";
1627 : }
1628 : }
1629 :
1630 : char *
1631 0 : mxid_to_string(MultiXactId multi, int nmembers, MultiXactMember *members)
1632 : {
1633 : static char *str = NULL;
1634 : StringInfoData buf;
1635 : int i;
1636 :
1637 0 : if (str != NULL)
1638 0 : pfree(str);
1639 :
1640 0 : initStringInfo(&buf);
1641 :
1642 0 : appendStringInfo(&buf, "%u %d[%u (%s)", multi, nmembers, members[0].xid,
1643 : mxstatus_to_string(members[0].status));
1644 :
1645 0 : for (i = 1; i < nmembers; i++)
1646 0 : appendStringInfo(&buf, ", %u (%s)", members[i].xid,
1647 0 : mxstatus_to_string(members[i].status));
1648 :
1649 0 : appendStringInfoChar(&buf, ']');
1650 0 : str = MemoryContextStrdup(TopMemoryContext, buf.data);
1651 0 : pfree(buf.data);
1652 0 : return str;
1653 : }
1654 :
1655 : /*
1656 : * AtEOXact_MultiXact
1657 : * Handle transaction end for MultiXact
1658 : *
1659 : * This is called at top transaction commit or abort (we don't care which).
1660 : */
1661 : void
1662 26161 : AtEOXact_MultiXact(void)
1663 : {
1664 : /*
1665 : * Reset our OldestMemberMXactId and OldestVisibleMXactId values, both of
1666 : * which should only be valid while within a transaction.
1667 : *
1668 : * We assume that storing a MultiXactId is atomic and so we need not take
1669 : * MultiXactGenLock to do this.
1670 : */
1671 26161 : OldestMemberMXactId[MyBackendId] = InvalidMultiXactId;
1672 26161 : OldestVisibleMXactId[MyBackendId] = InvalidMultiXactId;
1673 :
1674 : /*
1675 : * Discard the local MultiXactId cache. Since MXactContext was created as
1676 : * a child of TopTransactionContext, we needn't delete it explicitly.
1677 : */
1678 26161 : MXactContext = NULL;
1679 26161 : dlist_init(&MXactCache);
1680 26161 : MXactCacheMembers = 0;
1681 26161 : }
1682 :
1683 : /*
1684 : * AtPrepare_MultiXact
1685 : * Save multixact state at 2PC transaction prepare
1686 : *
1687 : * In this phase, we only store our OldestMemberMXactId value in the two-phase
1688 : * state file.
1689 : */
1690 : void
1691 6 : AtPrepare_MultiXact(void)
1692 : {
1693 6 : MultiXactId myOldestMember = OldestMemberMXactId[MyBackendId];
1694 :
1695 6 : if (MultiXactIdIsValid(myOldestMember))
1696 4 : RegisterTwoPhaseRecord(TWOPHASE_RM_MULTIXACT_ID, 0,
1697 : &myOldestMember, sizeof(MultiXactId));
1698 6 : }
1699 :
1700 : /*
1701 : * PostPrepare_MultiXact
1702 : * Clean up after successful PREPARE TRANSACTION
1703 : */
1704 : void
1705 6 : PostPrepare_MultiXact(TransactionId xid)
1706 : {
1707 : MultiXactId myOldestMember;
1708 :
1709 : /*
1710 : * Transfer our OldestMemberMXactId value to the slot reserved for the
1711 : * prepared transaction.
1712 : */
1713 6 : myOldestMember = OldestMemberMXactId[MyBackendId];
1714 6 : if (MultiXactIdIsValid(myOldestMember))
1715 : {
1716 4 : BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid);
1717 :
1718 : /*
1719 : * Even though storing MultiXactId is atomic, acquire lock to make
1720 : * sure others see both changes, not just the reset of the slot of the
1721 : * current backend. Using a volatile pointer might suffice, but this
1722 : * isn't a hot spot.
1723 : */
1724 4 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
1725 :
1726 4 : OldestMemberMXactId[dummyBackendId] = myOldestMember;
1727 4 : OldestMemberMXactId[MyBackendId] = InvalidMultiXactId;
1728 :
1729 4 : LWLockRelease(MultiXactGenLock);
1730 : }
1731 :
1732 : /*
1733 : * We don't need to transfer OldestVisibleMXactId value, because the
1734 : * transaction is not going to be looking at any more multixacts once it's
1735 : * prepared.
1736 : *
1737 : * We assume that storing a MultiXactId is atomic and so we need not take
1738 : * MultiXactGenLock to do this.
1739 : */
1740 6 : OldestVisibleMXactId[MyBackendId] = InvalidMultiXactId;
1741 :
1742 : /*
1743 : * Discard the local MultiXactId cache like in AtEOX_MultiXact
1744 : */
1745 6 : MXactContext = NULL;
1746 6 : dlist_init(&MXactCache);
1747 6 : MXactCacheMembers = 0;
1748 6 : }
1749 :
1750 : /*
1751 : * multixact_twophase_recover
1752 : * Recover the state of a prepared transaction at startup
1753 : */
1754 : void
1755 0 : multixact_twophase_recover(TransactionId xid, uint16 info,
1756 : void *recdata, uint32 len)
1757 : {
1758 0 : BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid);
1759 : MultiXactId oldestMember;
1760 :
1761 : /*
1762 : * Get the oldest member XID from the state file record, and set it in the
1763 : * OldestMemberMXactId slot reserved for this prepared transaction.
1764 : */
1765 0 : Assert(len == sizeof(MultiXactId));
1766 0 : oldestMember = *((MultiXactId *) recdata);
1767 :
1768 0 : OldestMemberMXactId[dummyBackendId] = oldestMember;
1769 0 : }
1770 :
1771 : /*
1772 : * multixact_twophase_postcommit
1773 : * Similar to AtEOX_MultiXact but for COMMIT PREPARED
1774 : */
1775 : void
1776 4 : multixact_twophase_postcommit(TransactionId xid, uint16 info,
1777 : void *recdata, uint32 len)
1778 : {
1779 4 : BackendId dummyBackendId = TwoPhaseGetDummyBackendId(xid);
1780 :
1781 4 : Assert(len == sizeof(MultiXactId));
1782 :
1783 4 : OldestMemberMXactId[dummyBackendId] = InvalidMultiXactId;
1784 4 : }
1785 :
1786 : /*
1787 : * multixact_twophase_postabort
1788 : * This is actually just the same as the COMMIT case.
1789 : */
1790 : void
1791 3 : multixact_twophase_postabort(TransactionId xid, uint16 info,
1792 : void *recdata, uint32 len)
1793 : {
1794 3 : multixact_twophase_postcommit(xid, info, recdata, len);
1795 3 : }
1796 :
1797 : /*
1798 : * Initialization of shared memory for MultiXact. We use two SLRU areas,
1799 : * thus double memory. Also, reserve space for the shared MultiXactState
1800 : * struct and the per-backend MultiXactId arrays (two of those, too).
1801 : */
1802 : Size
1803 5 : MultiXactShmemSize(void)
1804 : {
1805 : Size size;
1806 :
1807 : /* We need 2*MaxOldestSlot + 1 perBackendXactIds[] entries */
1808 : #define SHARED_MULTIXACT_STATE_SIZE \
1809 : add_size(offsetof(MultiXactStateData, perBackendXactIds) + sizeof(MultiXactId), \
1810 : mul_size(sizeof(MultiXactId) * 2, MaxOldestSlot))
1811 :
1812 5 : size = SHARED_MULTIXACT_STATE_SIZE;
1813 5 : size = add_size(size, SimpleLruShmemSize(NUM_MXACTOFFSET_BUFFERS, 0));
1814 5 : size = add_size(size, SimpleLruShmemSize(NUM_MXACTMEMBER_BUFFERS, 0));
1815 :
1816 5 : return size;
1817 : }
1818 :
1819 : void
1820 5 : MultiXactShmemInit(void)
1821 : {
1822 : bool found;
1823 :
1824 : debug_elog2(DEBUG2, "Shared Memory Init for MultiXact");
1825 :
1826 5 : MultiXactOffsetCtl->PagePrecedes = MultiXactOffsetPagePrecedes;
1827 5 : MultiXactMemberCtl->PagePrecedes = MultiXactMemberPagePrecedes;
1828 :
1829 5 : SimpleLruInit(MultiXactOffsetCtl,
1830 : "multixact_offset", NUM_MXACTOFFSET_BUFFERS, 0,
1831 5 : MultiXactOffsetControlLock, "pg_multixact/offsets",
1832 : LWTRANCHE_MXACTOFFSET_BUFFERS);
1833 5 : SimpleLruInit(MultiXactMemberCtl,
1834 : "multixact_member", NUM_MXACTMEMBER_BUFFERS, 0,
1835 5 : MultiXactMemberControlLock, "pg_multixact/members",
1836 : LWTRANCHE_MXACTMEMBER_BUFFERS);
1837 :
1838 : /* Initialize our shared state struct */
1839 5 : MultiXactState = ShmemInitStruct("Shared MultiXact State",
1840 5 : SHARED_MULTIXACT_STATE_SIZE,
1841 : &found);
1842 5 : if (!IsUnderPostmaster)
1843 : {
1844 5 : Assert(!found);
1845 :
1846 : /* Make sure we zero out the per-backend state */
1847 5 : MemSet(MultiXactState, 0, SHARED_MULTIXACT_STATE_SIZE);
1848 : }
1849 : else
1850 0 : Assert(found);
1851 :
1852 : /*
1853 : * Set up array pointers. Note that perBackendXactIds[0] is wasted space
1854 : * since we only use indexes 1..MaxOldestSlot in each array.
1855 : */
1856 5 : OldestMemberMXactId = MultiXactState->perBackendXactIds;
1857 5 : OldestVisibleMXactId = OldestMemberMXactId + MaxOldestSlot;
1858 5 : }
1859 :
1860 : /*
1861 : * This func must be called ONCE on system install. It creates the initial
1862 : * MultiXact segments. (The MultiXacts directories are assumed to have been
1863 : * created by initdb, and MultiXactShmemInit must have been called already.)
1864 : */
1865 : void
1866 1 : BootStrapMultiXact(void)
1867 : {
1868 : int slotno;
1869 :
1870 1 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1871 :
1872 : /* Create and zero the first page of the offsets log */
1873 1 : slotno = ZeroMultiXactOffsetPage(0, false);
1874 :
1875 : /* Make sure it's written out */
1876 1 : SimpleLruWritePage(MultiXactOffsetCtl, slotno);
1877 1 : Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
1878 :
1879 1 : LWLockRelease(MultiXactOffsetControlLock);
1880 :
1881 1 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
1882 :
1883 : /* Create and zero the first page of the members log */
1884 1 : slotno = ZeroMultiXactMemberPage(0, false);
1885 :
1886 : /* Make sure it's written out */
1887 1 : SimpleLruWritePage(MultiXactMemberCtl, slotno);
1888 1 : Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
1889 :
1890 1 : LWLockRelease(MultiXactMemberControlLock);
1891 1 : }
1892 :
1893 : /*
1894 : * Initialize (or reinitialize) a page of MultiXactOffset to zeroes.
1895 : * If writeXlog is TRUE, also emit an XLOG record saying we did this.
1896 : *
1897 : * The page is not actually written, just set up in shared memory.
1898 : * The slot number of the new page is returned.
1899 : *
1900 : * Control lock must be held at entry, and will be held at exit.
1901 : */
1902 : static int
1903 2 : ZeroMultiXactOffsetPage(int pageno, bool writeXlog)
1904 : {
1905 : int slotno;
1906 :
1907 2 : slotno = SimpleLruZeroPage(MultiXactOffsetCtl, pageno);
1908 :
1909 2 : if (writeXlog)
1910 1 : WriteMZeroPageXlogRec(pageno, XLOG_MULTIXACT_ZERO_OFF_PAGE);
1911 :
1912 2 : return slotno;
1913 : }
1914 :
1915 : /*
1916 : * Ditto, for MultiXactMember
1917 : */
1918 : static int
1919 2 : ZeroMultiXactMemberPage(int pageno, bool writeXlog)
1920 : {
1921 : int slotno;
1922 :
1923 2 : slotno = SimpleLruZeroPage(MultiXactMemberCtl, pageno);
1924 :
1925 2 : if (writeXlog)
1926 1 : WriteMZeroPageXlogRec(pageno, XLOG_MULTIXACT_ZERO_MEM_PAGE);
1927 :
1928 2 : return slotno;
1929 : }
1930 :
1931 : /*
1932 : * MaybeExtendOffsetSlru
1933 : * Extend the offsets SLRU area, if necessary
1934 : *
1935 : * After a binary upgrade from <= 9.2, the pg_multixact/offset SLRU area might
1936 : * contain files that are shorter than necessary; this would occur if the old
1937 : * installation had used multixacts beyond the first page (files cannot be
1938 : * copied, because the on-disk representation is different). pg_upgrade would
1939 : * update pg_control to set the next offset value to be at that position, so
1940 : * that tuples marked as locked by such MultiXacts would be seen as visible
1941 : * without having to consult multixact. However, trying to create and use a
1942 : * new MultiXactId would result in an error because the page on which the new
1943 : * value would reside does not exist. This routine is in charge of creating
1944 : * such pages.
1945 : */
1946 : static void
1947 0 : MaybeExtendOffsetSlru(void)
1948 : {
1949 : int pageno;
1950 :
1951 0 : pageno = MultiXactIdToOffsetPage(MultiXactState->nextMXact);
1952 :
1953 0 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
1954 :
1955 0 : if (!SimpleLruDoesPhysicalPageExist(MultiXactOffsetCtl, pageno))
1956 : {
1957 : int slotno;
1958 :
1959 : /*
1960 : * Fortunately for us, SimpleLruWritePage is already prepared to deal
1961 : * with creating a new segment file even if the page we're writing is
1962 : * not the first in it, so this is enough.
1963 : */
1964 0 : slotno = ZeroMultiXactOffsetPage(pageno, false);
1965 0 : SimpleLruWritePage(MultiXactOffsetCtl, slotno);
1966 : }
1967 :
1968 0 : LWLockRelease(MultiXactOffsetControlLock);
1969 0 : }
1970 :
1971 : /*
1972 : * This must be called ONCE during postmaster or standalone-backend startup.
1973 : *
1974 : * StartupXLOG has already established nextMXact/nextOffset by calling
1975 : * MultiXactSetNextMXact and/or MultiXactAdvanceNextMXact, and the oldestMulti
1976 : * info from pg_control and/or MultiXactAdvanceOldest, but we haven't yet
1977 : * replayed WAL.
1978 : */
1979 : void
1980 3 : StartupMultiXact(void)
1981 : {
1982 3 : MultiXactId multi = MultiXactState->nextMXact;
1983 3 : MultiXactOffset offset = MultiXactState->nextOffset;
1984 : int pageno;
1985 :
1986 : /*
1987 : * Initialize offset's idea of the latest page number.
1988 : */
1989 3 : pageno = MultiXactIdToOffsetPage(multi);
1990 3 : MultiXactOffsetCtl->shared->latest_page_number = pageno;
1991 :
1992 : /*
1993 : * Initialize member's idea of the latest page number.
1994 : */
1995 3 : pageno = MXOffsetToMemberPage(offset);
1996 3 : MultiXactMemberCtl->shared->latest_page_number = pageno;
1997 3 : }
1998 :
1999 : /*
2000 : * This must be called ONCE at the end of startup/recovery.
2001 : */
2002 : void
2003 3 : TrimMultiXact(void)
2004 : {
2005 : MultiXactId nextMXact;
2006 : MultiXactOffset offset;
2007 : MultiXactId oldestMXact;
2008 : Oid oldestMXactDB;
2009 : int pageno;
2010 : int entryno;
2011 : int flagsoff;
2012 :
2013 3 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2014 3 : nextMXact = MultiXactState->nextMXact;
2015 3 : offset = MultiXactState->nextOffset;
2016 3 : oldestMXact = MultiXactState->oldestMultiXactId;
2017 3 : oldestMXactDB = MultiXactState->oldestMultiXactDB;
2018 3 : LWLockRelease(MultiXactGenLock);
2019 :
2020 : /* Clean up offsets state */
2021 3 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
2022 :
2023 : /*
2024 : * (Re-)Initialize our idea of the latest page number for offsets.
2025 : */
2026 3 : pageno = MultiXactIdToOffsetPage(nextMXact);
2027 3 : MultiXactOffsetCtl->shared->latest_page_number = pageno;
2028 :
2029 : /*
2030 : * Zero out the remainder of the current offsets page. See notes in
2031 : * TrimCLOG() for background. Unlike CLOG, some WAL record covers every
2032 : * pg_multixact SLRU mutation. Since, also unlike CLOG, we ignore the WAL
2033 : * rule "write xlog before data," nextMXact successors may carry obsolete,
2034 : * nonzero offset values. Zero those so case 2 of GetMultiXactIdMembers()
2035 : * operates normally.
2036 : */
2037 3 : entryno = MultiXactIdToOffsetEntry(nextMXact);
2038 3 : if (entryno != 0)
2039 : {
2040 : int slotno;
2041 : MultiXactOffset *offptr;
2042 :
2043 3 : slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, nextMXact);
2044 3 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
2045 3 : offptr += entryno;
2046 :
2047 3 : MemSet(offptr, 0, BLCKSZ - (entryno * sizeof(MultiXactOffset)));
2048 :
2049 3 : MultiXactOffsetCtl->shared->page_dirty[slotno] = true;
2050 : }
2051 :
2052 3 : LWLockRelease(MultiXactOffsetControlLock);
2053 :
2054 : /* And the same for members */
2055 3 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
2056 :
2057 : /*
2058 : * (Re-)Initialize our idea of the latest page number for members.
2059 : */
2060 3 : pageno = MXOffsetToMemberPage(offset);
2061 3 : MultiXactMemberCtl->shared->latest_page_number = pageno;
2062 :
2063 : /*
2064 : * Zero out the remainder of the current members page. See notes in
2065 : * TrimCLOG() for motivation.
2066 : */
2067 3 : flagsoff = MXOffsetToFlagsOffset(offset);
2068 3 : if (flagsoff != 0)
2069 : {
2070 : int slotno;
2071 : TransactionId *xidptr;
2072 : int memberoff;
2073 :
2074 0 : memberoff = MXOffsetToMemberOffset(offset);
2075 0 : slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, offset);
2076 0 : xidptr = (TransactionId *)
2077 0 : (MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
2078 :
2079 0 : MemSet(xidptr, 0, BLCKSZ - memberoff);
2080 :
2081 : /*
2082 : * Note: we don't need to zero out the flag bits in the remaining
2083 : * members of the current group, because they are always reset before
2084 : * writing.
2085 : */
2086 :
2087 0 : MultiXactMemberCtl->shared->page_dirty[slotno] = true;
2088 : }
2089 :
2090 3 : LWLockRelease(MultiXactMemberControlLock);
2091 :
2092 : /* signal that we're officially up */
2093 3 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2094 3 : MultiXactState->finishedStartup = true;
2095 3 : LWLockRelease(MultiXactGenLock);
2096 :
2097 : /* Now compute how far away the next members wraparound is. */
2098 3 : SetMultiXactIdLimit(oldestMXact, oldestMXactDB, true);
2099 3 : }
2100 :
2101 : /*
2102 : * This must be called ONCE during postmaster or standalone-backend shutdown
2103 : */
2104 : void
2105 3 : ShutdownMultiXact(void)
2106 : {
2107 : /* Flush dirty MultiXact pages to disk */
2108 : TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(false);
2109 3 : SimpleLruFlush(MultiXactOffsetCtl, false);
2110 3 : SimpleLruFlush(MultiXactMemberCtl, false);
2111 : TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(false);
2112 3 : }
2113 :
2114 : /*
2115 : * Get the MultiXact data to save in a checkpoint record
2116 : */
2117 : void
2118 11 : MultiXactGetCheckptMulti(bool is_shutdown,
2119 : MultiXactId *nextMulti,
2120 : MultiXactOffset *nextMultiOffset,
2121 : MultiXactId *oldestMulti,
2122 : Oid *oldestMultiDB)
2123 : {
2124 11 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2125 11 : *nextMulti = MultiXactState->nextMXact;
2126 11 : *nextMultiOffset = MultiXactState->nextOffset;
2127 11 : *oldestMulti = MultiXactState->oldestMultiXactId;
2128 11 : *oldestMultiDB = MultiXactState->oldestMultiXactDB;
2129 11 : LWLockRelease(MultiXactGenLock);
2130 :
2131 : debug_elog6(DEBUG2,
2132 : "MultiXact: checkpoint is nextMulti %u, nextOffset %u, oldestMulti %u in DB %u",
2133 : *nextMulti, *nextMultiOffset, *oldestMulti, *oldestMultiDB);
2134 11 : }
2135 :
2136 : /*
2137 : * Perform a checkpoint --- either during shutdown, or on-the-fly
2138 : */
2139 : void
2140 11 : CheckPointMultiXact(void)
2141 : {
2142 : TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_START(true);
2143 :
2144 : /* Flush dirty MultiXact pages to disk */
2145 11 : SimpleLruFlush(MultiXactOffsetCtl, true);
2146 11 : SimpleLruFlush(MultiXactMemberCtl, true);
2147 :
2148 : TRACE_POSTGRESQL_MULTIXACT_CHECKPOINT_DONE(true);
2149 11 : }
2150 :
2151 : /*
2152 : * Set the next-to-be-assigned MultiXactId and offset
2153 : *
2154 : * This is used when we can determine the correct next ID/offset exactly
2155 : * from a checkpoint record. Although this is only called during bootstrap
2156 : * and XLog replay, we take the lock in case any hot-standby backends are
2157 : * examining the values.
2158 : */
2159 : void
2160 4 : MultiXactSetNextMXact(MultiXactId nextMulti,
2161 : MultiXactOffset nextMultiOffset)
2162 : {
2163 : debug_elog4(DEBUG2, "MultiXact: setting next multi to %u offset %u",
2164 : nextMulti, nextMultiOffset);
2165 4 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2166 4 : MultiXactState->nextMXact = nextMulti;
2167 4 : MultiXactState->nextOffset = nextMultiOffset;
2168 4 : LWLockRelease(MultiXactGenLock);
2169 :
2170 : /*
2171 : * During a binary upgrade, make sure that the offsets SLRU is large
2172 : * enough to contain the next value that would be created.
2173 : *
2174 : * We need to do this pretty early during the first startup in binary
2175 : * upgrade mode: before StartupMultiXact() in fact, because this routine
2176 : * is called even before that by StartupXLOG(). And we can't do it
2177 : * earlier than at this point, because during that first call of this
2178 : * routine we determine the MultiXactState->nextMXact value that
2179 : * MaybeExtendOffsetSlru needs.
2180 : */
2181 4 : if (IsBinaryUpgrade)
2182 0 : MaybeExtendOffsetSlru();
2183 4 : }
2184 :
2185 : /*
2186 : * Determine the last safe MultiXactId to allocate given the currently oldest
2187 : * datminmxid (ie, the oldest MultiXactId that might exist in any database
2188 : * of our cluster), and the OID of the (or a) database with that value.
2189 : *
2190 : * is_startup is true when we are just starting the cluster, false when we
2191 : * are updating state in a running cluster. This only affects log messages.
2192 : */
2193 : void
2194 9 : SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
2195 : bool is_startup)
2196 : {
2197 : MultiXactId multiVacLimit;
2198 : MultiXactId multiWarnLimit;
2199 : MultiXactId multiStopLimit;
2200 : MultiXactId multiWrapLimit;
2201 : MultiXactId curMulti;
2202 : bool needs_offset_vacuum;
2203 :
2204 9 : Assert(MultiXactIdIsValid(oldest_datminmxid));
2205 :
2206 : /*
2207 : * We pretend that a wrap will happen halfway through the multixact ID
2208 : * space, but that's not really true, because multixacts wrap differently
2209 : * from transaction IDs. Note that, separately from any concern about
2210 : * multixact IDs wrapping, we must ensure that multixact members do not
2211 : * wrap. Limits for that are set in DetermineSafeOldestOffset, not here.
2212 : */
2213 9 : multiWrapLimit = oldest_datminmxid + (MaxMultiXactId >> 1);
2214 9 : if (multiWrapLimit < FirstMultiXactId)
2215 0 : multiWrapLimit += FirstMultiXactId;
2216 :
2217 : /*
2218 : * We'll refuse to continue assigning MultiXactIds once we get within 100
2219 : * multi of data loss.
2220 : *
2221 : * Note: This differs from the magic number used in
2222 : * SetTransactionIdLimit() since vacuum itself will never generate new
2223 : * multis. XXX actually it does, if it needs to freeze old multis.
2224 : */
2225 9 : multiStopLimit = multiWrapLimit - 100;
2226 9 : if (multiStopLimit < FirstMultiXactId)
2227 0 : multiStopLimit -= FirstMultiXactId;
2228 :
2229 : /*
2230 : * We'll start complaining loudly when we get within 10M multis of the
2231 : * stop point. This is kind of arbitrary, but if you let your gas gauge
2232 : * get down to 1% of full, would you be looking for the next gas station?
2233 : * We need to be fairly liberal about this number because there are lots
2234 : * of scenarios where most transactions are done by automatic clients that
2235 : * won't pay attention to warnings. (No, we're not gonna make this
2236 : * configurable. If you know enough to configure it, you know enough to
2237 : * not get in this kind of trouble in the first place.)
2238 : */
2239 9 : multiWarnLimit = multiStopLimit - 10000000;
2240 9 : if (multiWarnLimit < FirstMultiXactId)
2241 0 : multiWarnLimit -= FirstMultiXactId;
2242 :
2243 : /*
2244 : * We'll start trying to force autovacuums when oldest_datminmxid gets to
2245 : * be more than autovacuum_multixact_freeze_max_age mxids old.
2246 : *
2247 : * Note: autovacuum_multixact_freeze_max_age is a PGC_POSTMASTER parameter
2248 : * so that we don't have to worry about dealing with on-the-fly changes in
2249 : * its value. See SetTransactionIdLimit.
2250 : */
2251 9 : multiVacLimit = oldest_datminmxid + autovacuum_multixact_freeze_max_age;
2252 9 : if (multiVacLimit < FirstMultiXactId)
2253 0 : multiVacLimit += FirstMultiXactId;
2254 :
2255 : /* Grab lock for just long enough to set the new limit values */
2256 9 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2257 9 : MultiXactState->oldestMultiXactId = oldest_datminmxid;
2258 9 : MultiXactState->oldestMultiXactDB = oldest_datoid;
2259 9 : MultiXactState->multiVacLimit = multiVacLimit;
2260 9 : MultiXactState->multiWarnLimit = multiWarnLimit;
2261 9 : MultiXactState->multiStopLimit = multiStopLimit;
2262 9 : MultiXactState->multiWrapLimit = multiWrapLimit;
2263 9 : curMulti = MultiXactState->nextMXact;
2264 9 : LWLockRelease(MultiXactGenLock);
2265 :
2266 : /* Log the info */
2267 9 : ereport(DEBUG1,
2268 : (errmsg("MultiXactId wrap limit is %u, limited by database with OID %u",
2269 : multiWrapLimit, oldest_datoid)));
2270 :
2271 : /*
2272 : * Computing the actual limits is only possible once the data directory is
2273 : * in a consistent state. There's no need to compute the limits while
2274 : * still replaying WAL - no decisions about new multis are made even
2275 : * though multixact creations might be replayed. So we'll only do further
2276 : * checks after TrimMultiXact() has been called.
2277 : */
2278 9 : if (!MultiXactState->finishedStartup)
2279 13 : return;
2280 :
2281 5 : Assert(!InRecovery);
2282 :
2283 : /* Set limits for offset vacuum. */
2284 5 : needs_offset_vacuum = SetOffsetVacuumLimit(is_startup);
2285 :
2286 : /*
2287 : * If past the autovacuum force point, immediately signal an autovac
2288 : * request. The reason for this is that autovac only processes one
2289 : * database per invocation. Once it's finished cleaning up the oldest
2290 : * database, it'll call here, and we'll signal the postmaster to start
2291 : * another iteration immediately if there are still any old databases.
2292 : */
2293 5 : if ((MultiXactIdPrecedes(multiVacLimit, curMulti) ||
2294 0 : needs_offset_vacuum) && IsUnderPostmaster)
2295 0 : SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
2296 :
2297 : /* Give an immediate warning if past the wrap warn point */
2298 5 : if (MultiXactIdPrecedes(multiWarnLimit, curMulti))
2299 : {
2300 : char *oldest_datname;
2301 :
2302 : /*
2303 : * We can be called when not inside a transaction, for example during
2304 : * StartupXLOG(). In such a case we cannot do database access, so we
2305 : * must just report the oldest DB's OID.
2306 : *
2307 : * Note: it's also possible that get_database_name fails and returns
2308 : * NULL, for example because the database just got dropped. We'll
2309 : * still warn, even though the warning might now be unnecessary.
2310 : */
2311 0 : if (IsTransactionState())
2312 0 : oldest_datname = get_database_name(oldest_datoid);
2313 : else
2314 0 : oldest_datname = NULL;
2315 :
2316 0 : if (oldest_datname)
2317 0 : ereport(WARNING,
2318 : (errmsg_plural("database \"%s\" must be vacuumed before %u more MultiXactId is used",
2319 : "database \"%s\" must be vacuumed before %u more MultiXactIds are used",
2320 : multiWrapLimit - curMulti,
2321 : oldest_datname,
2322 : multiWrapLimit - curMulti),
2323 : errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
2324 : "You might also need to commit or roll back old prepared transactions.")));
2325 : else
2326 0 : ereport(WARNING,
2327 : (errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
2328 : "database with OID %u must be vacuumed before %u more MultiXactIds are used",
2329 : multiWrapLimit - curMulti,
2330 : oldest_datoid,
2331 : multiWrapLimit - curMulti),
2332 : errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
2333 : "You might also need to commit or roll back old prepared transactions.")));
2334 : }
2335 : }
2336 :
2337 : /*
2338 : * Ensure the next-to-be-assigned MultiXactId is at least minMulti,
2339 : * and similarly nextOffset is at least minMultiOffset.
2340 : *
2341 : * This is used when we can determine minimum safe values from an XLog
2342 : * record (either an on-line checkpoint or an mxact creation log entry).
2343 : * Although this is only called during XLog replay, we take the lock in case
2344 : * any hot-standby backends are examining the values.
2345 : */
2346 : void
2347 0 : MultiXactAdvanceNextMXact(MultiXactId minMulti,
2348 : MultiXactOffset minMultiOffset)
2349 : {
2350 0 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2351 0 : if (MultiXactIdPrecedes(MultiXactState->nextMXact, minMulti))
2352 : {
2353 : debug_elog3(DEBUG2, "MultiXact: setting next multi to %u", minMulti);
2354 0 : MultiXactState->nextMXact = minMulti;
2355 : }
2356 0 : if (MultiXactOffsetPrecedes(MultiXactState->nextOffset, minMultiOffset))
2357 : {
2358 : debug_elog3(DEBUG2, "MultiXact: setting next offset to %u",
2359 : minMultiOffset);
2360 0 : MultiXactState->nextOffset = minMultiOffset;
2361 : }
2362 0 : LWLockRelease(MultiXactGenLock);
2363 0 : }
2364 :
2365 : /*
2366 : * Update our oldestMultiXactId value, but only if it's more recent than what
2367 : * we had.
2368 : *
2369 : * This may only be called during WAL replay.
2370 : */
2371 : void
2372 0 : MultiXactAdvanceOldest(MultiXactId oldestMulti, Oid oldestMultiDB)
2373 : {
2374 0 : Assert(InRecovery);
2375 :
2376 0 : if (MultiXactIdPrecedes(MultiXactState->oldestMultiXactId, oldestMulti))
2377 0 : SetMultiXactIdLimit(oldestMulti, oldestMultiDB, false);
2378 0 : }
2379 :
2380 : /*
2381 : * Make sure that MultiXactOffset has room for a newly-allocated MultiXactId.
2382 : *
2383 : * NB: this is called while holding MultiXactGenLock. We want it to be very
2384 : * fast most of the time; even when it's not so fast, no actual I/O need
2385 : * happen unless we're forced to write out a dirty log or xlog page to make
2386 : * room in shared memory.
2387 : */
2388 : static void
2389 2 : ExtendMultiXactOffset(MultiXactId multi)
2390 : {
2391 : int pageno;
2392 :
2393 : /*
2394 : * No work except at first MultiXactId of a page. But beware: just after
2395 : * wraparound, the first MultiXactId of page zero is FirstMultiXactId.
2396 : */
2397 2 : if (MultiXactIdToOffsetEntry(multi) != 0 &&
2398 : multi != FirstMultiXactId)
2399 3 : return;
2400 :
2401 1 : pageno = MultiXactIdToOffsetPage(multi);
2402 :
2403 1 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
2404 :
2405 : /* Zero the page and make an XLOG entry about it */
2406 1 : ZeroMultiXactOffsetPage(pageno, true);
2407 :
2408 1 : LWLockRelease(MultiXactOffsetControlLock);
2409 : }
2410 :
2411 : /*
2412 : * Make sure that MultiXactMember has room for the members of a newly-
2413 : * allocated MultiXactId.
2414 : *
2415 : * Like the above routine, this is called while holding MultiXactGenLock;
2416 : * same comments apply.
2417 : */
2418 : static void
2419 2 : ExtendMultiXactMember(MultiXactOffset offset, int nmembers)
2420 : {
2421 : /*
2422 : * It's possible that the members span more than one page of the members
2423 : * file, so we loop to ensure we consider each page. The coding is not
2424 : * optimal if the members span several pages, but that seems unusual
2425 : * enough to not worry much about.
2426 : */
2427 6 : while (nmembers > 0)
2428 : {
2429 : int flagsoff;
2430 : int flagsbit;
2431 : uint32 difference;
2432 :
2433 : /*
2434 : * Only zero when at first entry of a page.
2435 : */
2436 2 : flagsoff = MXOffsetToFlagsOffset(offset);
2437 2 : flagsbit = MXOffsetToFlagsBitShift(offset);
2438 2 : if (flagsoff == 0 && flagsbit == 0)
2439 : {
2440 : int pageno;
2441 :
2442 1 : pageno = MXOffsetToMemberPage(offset);
2443 :
2444 1 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
2445 :
2446 : /* Zero the page and make an XLOG entry about it */
2447 1 : ZeroMultiXactMemberPage(pageno, true);
2448 :
2449 1 : LWLockRelease(MultiXactMemberControlLock);
2450 : }
2451 :
2452 : /*
2453 : * Compute the number of items till end of current page. Careful: if
2454 : * addition of unsigned ints wraps around, we're at the last page of
2455 : * the last segment; since that page holds a different number of items
2456 : * than other pages, we need to do it differently.
2457 : */
2458 2 : if (offset + MAX_MEMBERS_IN_LAST_MEMBERS_PAGE < offset)
2459 : {
2460 : /*
2461 : * This is the last page of the last segment; we can compute the
2462 : * number of items left to allocate in it without modulo
2463 : * arithmetic.
2464 : */
2465 0 : difference = MaxMultiXactOffset - offset + 1;
2466 : }
2467 : else
2468 2 : difference = MULTIXACT_MEMBERS_PER_PAGE - offset % MULTIXACT_MEMBERS_PER_PAGE;
2469 :
2470 : /*
2471 : * Advance to next page, taking care to properly handle the wraparound
2472 : * case. OK if nmembers goes negative.
2473 : */
2474 2 : nmembers -= difference;
2475 2 : offset += difference;
2476 : }
2477 2 : }
2478 :
2479 : /*
2480 : * GetOldestMultiXactId
2481 : *
2482 : * Return the oldest MultiXactId that's still possibly still seen as live by
2483 : * any running transaction. Older ones might still exist on disk, but they no
2484 : * longer have any running member transaction.
2485 : *
2486 : * It's not safe to truncate MultiXact SLRU segments on the value returned by
2487 : * this function; however, it can be used by a full-table vacuum to set the
2488 : * point at which it will be possible to truncate SLRU for that table.
2489 : */
2490 : MultiXactId
2491 2856 : GetOldestMultiXactId(void)
2492 : {
2493 : MultiXactId oldestMXact;
2494 : MultiXactId nextMXact;
2495 : int i;
2496 :
2497 : /*
2498 : * This is the oldest valid value among all the OldestMemberMXactId[] and
2499 : * OldestVisibleMXactId[] entries, or nextMXact if none are valid.
2500 : */
2501 2856 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2502 :
2503 : /*
2504 : * We have to beware of the possibility that nextMXact is in the
2505 : * wrapped-around state. We don't fix the counter itself here, but we
2506 : * must be sure to use a valid value in our calculation.
2507 : */
2508 2856 : nextMXact = MultiXactState->nextMXact;
2509 2856 : if (nextMXact < FirstMultiXactId)
2510 0 : nextMXact = FirstMultiXactId;
2511 :
2512 2856 : oldestMXact = nextMXact;
2513 328074 : for (i = 1; i <= MaxOldestSlot; i++)
2514 : {
2515 : MultiXactId thisoldest;
2516 :
2517 325218 : thisoldest = OldestMemberMXactId[i];
2518 326280 : if (MultiXactIdIsValid(thisoldest) &&
2519 1062 : MultiXactIdPrecedes(thisoldest, oldestMXact))
2520 0 : oldestMXact = thisoldest;
2521 325218 : thisoldest = OldestVisibleMXactId[i];
2522 325218 : if (MultiXactIdIsValid(thisoldest) &&
2523 0 : MultiXactIdPrecedes(thisoldest, oldestMXact))
2524 0 : oldestMXact = thisoldest;
2525 : }
2526 :
2527 2856 : LWLockRelease(MultiXactGenLock);
2528 :
2529 2856 : return oldestMXact;
2530 : }
2531 :
2532 : /*
2533 : * Determine how aggressively we need to vacuum in order to prevent member
2534 : * wraparound.
2535 : *
2536 : * To do so determine what's the oldest member offset and install the limit
2537 : * info in MultiXactState, where it can be used to prevent overrun of old data
2538 : * in the members SLRU area.
2539 : *
2540 : * The return value is true if emergency autovacuum is required and false
2541 : * otherwise.
2542 : */
2543 : static bool
2544 5 : SetOffsetVacuumLimit(bool is_startup)
2545 : {
2546 : MultiXactId oldestMultiXactId;
2547 : MultiXactId nextMXact;
2548 5 : MultiXactOffset oldestOffset = 0; /* placate compiler */
2549 : MultiXactOffset prevOldestOffset;
2550 : MultiXactOffset nextOffset;
2551 5 : bool oldestOffsetKnown = false;
2552 : bool prevOldestOffsetKnown;
2553 5 : MultiXactOffset offsetStopLimit = 0;
2554 : MultiXactOffset prevOffsetStopLimit;
2555 :
2556 : /*
2557 : * NB: Have to prevent concurrent truncation, we might otherwise try to
2558 : * lookup a oldestMulti that's concurrently getting truncated away.
2559 : */
2560 5 : LWLockAcquire(MultiXactTruncationLock, LW_SHARED);
2561 :
2562 : /* Read relevant fields from shared memory. */
2563 5 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2564 5 : oldestMultiXactId = MultiXactState->oldestMultiXactId;
2565 5 : nextMXact = MultiXactState->nextMXact;
2566 5 : nextOffset = MultiXactState->nextOffset;
2567 5 : prevOldestOffsetKnown = MultiXactState->oldestOffsetKnown;
2568 5 : prevOldestOffset = MultiXactState->oldestOffset;
2569 5 : prevOffsetStopLimit = MultiXactState->offsetStopLimit;
2570 5 : Assert(MultiXactState->finishedStartup);
2571 5 : LWLockRelease(MultiXactGenLock);
2572 :
2573 : /*
2574 : * Determine the offset of the oldest multixact. Normally, we can read
2575 : * the offset from the multixact itself, but there's an important special
2576 : * case: if there are no multixacts in existence at all, oldestMXact
2577 : * obviously can't point to one. It will instead point to the multixact
2578 : * ID that will be assigned the next time one is needed.
2579 : */
2580 5 : if (oldestMultiXactId == nextMXact)
2581 : {
2582 : /*
2583 : * When the next multixact gets created, it will be stored at the next
2584 : * offset.
2585 : */
2586 5 : oldestOffset = nextOffset;
2587 5 : oldestOffsetKnown = true;
2588 : }
2589 : else
2590 : {
2591 : /*
2592 : * Figure out where the oldest existing multixact's offsets are
2593 : * stored. Due to bugs in early release of PostgreSQL 9.3.X and 9.4.X,
2594 : * the supposedly-earliest multixact might not really exist. We are
2595 : * careful not to fail in that case.
2596 : */
2597 0 : oldestOffsetKnown =
2598 : find_multixact_start(oldestMultiXactId, &oldestOffset);
2599 :
2600 0 : if (oldestOffsetKnown)
2601 0 : ereport(DEBUG1,
2602 : (errmsg("oldest MultiXactId member is at offset %u",
2603 : oldestOffset)));
2604 : else
2605 0 : ereport(LOG,
2606 : (errmsg("MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact %u does not exist on disk",
2607 : oldestMultiXactId)));
2608 : }
2609 :
2610 5 : LWLockRelease(MultiXactTruncationLock);
2611 :
2612 : /*
2613 : * If we can, compute limits (and install them MultiXactState) to prevent
2614 : * overrun of old data in the members SLRU area. We can only do so if the
2615 : * oldest offset is known though.
2616 : */
2617 5 : if (oldestOffsetKnown)
2618 : {
2619 : /* move back to start of the corresponding segment */
2620 5 : offsetStopLimit = oldestOffset - (oldestOffset %
2621 : (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT));
2622 :
2623 : /* always leave one segment before the wraparound point */
2624 5 : offsetStopLimit -= (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT);
2625 :
2626 5 : if (!prevOldestOffsetKnown && !is_startup)
2627 0 : ereport(LOG,
2628 : (errmsg("MultiXact member wraparound protections are now enabled")));
2629 :
2630 5 : ereport(DEBUG1,
2631 : (errmsg("MultiXact member stop limit is now %u based on MultiXact %u",
2632 : offsetStopLimit, oldestMultiXactId)));
2633 : }
2634 0 : else if (prevOldestOffsetKnown)
2635 : {
2636 : /*
2637 : * If we failed to get the oldest offset this time, but we have a
2638 : * value from a previous pass through this function, use the old
2639 : * values rather than automatically forcing an emergency autovacuum
2640 : * cycle again.
2641 : */
2642 0 : oldestOffset = prevOldestOffset;
2643 0 : oldestOffsetKnown = true;
2644 0 : offsetStopLimit = prevOffsetStopLimit;
2645 : }
2646 :
2647 : /* Install the computed values */
2648 5 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
2649 5 : MultiXactState->oldestOffset = oldestOffset;
2650 5 : MultiXactState->oldestOffsetKnown = oldestOffsetKnown;
2651 5 : MultiXactState->offsetStopLimit = offsetStopLimit;
2652 5 : LWLockRelease(MultiXactGenLock);
2653 :
2654 : /*
2655 : * Do we need an emergency autovacuum? If we're not sure, assume yes.
2656 : */
2657 10 : return !oldestOffsetKnown ||
2658 5 : (nextOffset - oldestOffset > MULTIXACT_MEMBER_SAFE_THRESHOLD);
2659 : }
2660 :
2661 : /*
2662 : * Return whether adding "distance" to "start" would move past "boundary".
2663 : *
2664 : * We use this to determine whether the addition is "wrapping around" the
2665 : * boundary point, hence the name. The reason we don't want to use the regular
2666 : * 2^31-modulo arithmetic here is that we want to be able to use the whole of
2667 : * the 2^32-1 space here, allowing for more multixacts that would fit
2668 : * otherwise.
2669 : */
2670 : static bool
2671 4 : MultiXactOffsetWouldWrap(MultiXactOffset boundary, MultiXactOffset start,
2672 : uint32 distance)
2673 : {
2674 : MultiXactOffset finish;
2675 :
2676 : /*
2677 : * Note that offset number 0 is not used (see GetMultiXactIdMembers), so
2678 : * if the addition wraps around the UINT_MAX boundary, skip that value.
2679 : */
2680 4 : finish = start + distance;
2681 4 : if (finish < start)
2682 0 : finish++;
2683 :
2684 : /*-----------------------------------------------------------------------
2685 : * When the boundary is numerically greater than the starting point, any
2686 : * value numerically between the two is not wrapped:
2687 : *
2688 : * <----S----B---->
2689 : * [---) = F wrapped past B (and UINT_MAX)
2690 : * [---) = F not wrapped
2691 : * [----] = F wrapped past B
2692 : *
2693 : * When the boundary is numerically less than the starting point (i.e. the
2694 : * UINT_MAX wraparound occurs somewhere in between) then all values in
2695 : * between are wrapped:
2696 : *
2697 : * <----B----S---->
2698 : * [---) = F not wrapped past B (but wrapped past UINT_MAX)
2699 : * [---) = F wrapped past B (and UINT_MAX)
2700 : * [----] = F not wrapped
2701 : *-----------------------------------------------------------------------
2702 : */
2703 4 : if (start < boundary)
2704 4 : return finish >= boundary || finish < start;
2705 : else
2706 0 : return finish >= boundary && finish < start;
2707 : }
2708 :
2709 : /*
2710 : * Find the starting offset of the given MultiXactId.
2711 : *
2712 : * Returns false if the file containing the multi does not exist on disk.
2713 : * Otherwise, returns true and sets *result to the starting member offset.
2714 : *
2715 : * This function does not prevent concurrent truncation, so if that's
2716 : * required, the caller has to protect against that.
2717 : */
2718 : static bool
2719 0 : find_multixact_start(MultiXactId multi, MultiXactOffset *result)
2720 : {
2721 : MultiXactOffset offset;
2722 : int pageno;
2723 : int entryno;
2724 : int slotno;
2725 : MultiXactOffset *offptr;
2726 :
2727 0 : Assert(MultiXactState->finishedStartup);
2728 :
2729 0 : pageno = MultiXactIdToOffsetPage(multi);
2730 0 : entryno = MultiXactIdToOffsetEntry(multi);
2731 :
2732 : /*
2733 : * Flush out dirty data, so PhysicalPageExists can work correctly.
2734 : * SimpleLruFlush() is a pretty big hammer for that. Alternatively we
2735 : * could add a in-memory version of page exists, but find_multixact_start
2736 : * is called infrequently, and it doesn't seem bad to flush buffers to
2737 : * disk before truncation.
2738 : */
2739 0 : SimpleLruFlush(MultiXactOffsetCtl, true);
2740 0 : SimpleLruFlush(MultiXactMemberCtl, true);
2741 :
2742 0 : if (!SimpleLruDoesPhysicalPageExist(MultiXactOffsetCtl, pageno))
2743 0 : return false;
2744 :
2745 : /* lock is acquired by SimpleLruReadPage_ReadOnly */
2746 0 : slotno = SimpleLruReadPage_ReadOnly(MultiXactOffsetCtl, pageno, multi);
2747 0 : offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno];
2748 0 : offptr += entryno;
2749 0 : offset = *offptr;
2750 0 : LWLockRelease(MultiXactOffsetControlLock);
2751 :
2752 0 : *result = offset;
2753 0 : return true;
2754 : }
2755 :
2756 : /*
2757 : * Determine how many multixacts, and how many multixact members, currently
2758 : * exist. Return false if unable to determine.
2759 : */
2760 : static bool
2761 415 : ReadMultiXactCounts(uint32 *multixacts, MultiXactOffset *members)
2762 : {
2763 : MultiXactOffset nextOffset;
2764 : MultiXactOffset oldestOffset;
2765 : MultiXactId oldestMultiXactId;
2766 : MultiXactId nextMultiXactId;
2767 : bool oldestOffsetKnown;
2768 :
2769 415 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2770 415 : nextOffset = MultiXactState->nextOffset;
2771 415 : oldestMultiXactId = MultiXactState->oldestMultiXactId;
2772 415 : nextMultiXactId = MultiXactState->nextMXact;
2773 415 : oldestOffset = MultiXactState->oldestOffset;
2774 415 : oldestOffsetKnown = MultiXactState->oldestOffsetKnown;
2775 415 : LWLockRelease(MultiXactGenLock);
2776 :
2777 415 : if (!oldestOffsetKnown)
2778 0 : return false;
2779 :
2780 415 : *members = nextOffset - oldestOffset;
2781 415 : *multixacts = nextMultiXactId - oldestMultiXactId;
2782 415 : return true;
2783 : }
2784 :
2785 : /*
2786 : * Multixact members can be removed once the multixacts that refer to them
2787 : * are older than every datminxmid. autovacuum_multixact_freeze_max_age and
2788 : * vacuum_multixact_freeze_table_age work together to make sure we never have
2789 : * too many multixacts; we hope that, at least under normal circumstances,
2790 : * this will also be sufficient to keep us from using too many offsets.
2791 : * However, if the average multixact has many members, we might exhaust the
2792 : * members space while still using few enough members that these limits fail
2793 : * to trigger full table scans for relminmxid advancement. At that point,
2794 : * we'd have no choice but to start failing multixact-creating operations
2795 : * with an error.
2796 : *
2797 : * To prevent that, if more than a threshold portion of the members space is
2798 : * used, we effectively reduce autovacuum_multixact_freeze_max_age and
2799 : * to a value just less than the number of multixacts in use. We hope that
2800 : * this will quickly trigger autovacuuming on the table or tables with the
2801 : * oldest relminmxid, thus allowing datminmxid values to advance and removing
2802 : * some members.
2803 : *
2804 : * As the fraction of the member space currently in use grows, we become
2805 : * more aggressive in clamping this value. That not only causes autovacuum
2806 : * to ramp up, but also makes any manual vacuums the user issues more
2807 : * aggressive. This happens because vacuum_set_xid_limits() clamps the
2808 : * freeze table and the minimum freeze age based on the effective
2809 : * autovacuum_multixact_freeze_max_age this function returns. In the worst
2810 : * case, we'll claim the freeze_max_age to zero, and every vacuum of any
2811 : * table will try to freeze every multixact.
2812 : *
2813 : * It's possible that these thresholds should be user-tunable, but for now
2814 : * we keep it simple.
2815 : */
2816 : int
2817 415 : MultiXactMemberFreezeThreshold(void)
2818 : {
2819 : MultiXactOffset members;
2820 : uint32 multixacts;
2821 : uint32 victim_multixacts;
2822 : double fraction;
2823 :
2824 : /* If we can't determine member space utilization, assume the worst. */
2825 415 : if (!ReadMultiXactCounts(&multixacts, &members))
2826 0 : return 0;
2827 :
2828 : /* If member space utilization is low, no special action is required. */
2829 415 : if (members <= MULTIXACT_MEMBER_SAFE_THRESHOLD)
2830 415 : return autovacuum_multixact_freeze_max_age;
2831 :
2832 : /*
2833 : * Compute a target for relminmxid advancement. The number of multixacts
2834 : * we try to eliminate from the system is based on how far we are past
2835 : * MULTIXACT_MEMBER_SAFE_THRESHOLD.
2836 : */
2837 0 : fraction = (double) (members - MULTIXACT_MEMBER_SAFE_THRESHOLD) /
2838 : (MULTIXACT_MEMBER_DANGER_THRESHOLD - MULTIXACT_MEMBER_SAFE_THRESHOLD);
2839 0 : victim_multixacts = multixacts * fraction;
2840 :
2841 : /* fraction could be > 1.0, but lowest possible freeze age is zero */
2842 0 : if (victim_multixacts > multixacts)
2843 0 : return 0;
2844 0 : return multixacts - victim_multixacts;
2845 : }
2846 :
2847 : typedef struct mxtruncinfo
2848 : {
2849 : int earliestExistingPage;
2850 : } mxtruncinfo;
2851 :
2852 : /*
2853 : * SlruScanDirectory callback
2854 : * This callback determines the earliest existing page number.
2855 : */
2856 : static bool
2857 0 : SlruScanDirCbFindEarliest(SlruCtl ctl, char *filename, int segpage, void *data)
2858 : {
2859 0 : mxtruncinfo *trunc = (mxtruncinfo *) data;
2860 :
2861 0 : if (trunc->earliestExistingPage == -1 ||
2862 0 : ctl->PagePrecedes(segpage, trunc->earliestExistingPage))
2863 : {
2864 0 : trunc->earliestExistingPage = segpage;
2865 : }
2866 :
2867 0 : return false; /* keep going */
2868 : }
2869 :
2870 :
2871 : /*
2872 : * Delete members segments [oldest, newOldest)
2873 : *
2874 : * The members SLRU can, in contrast to the offsets one, be filled to almost
2875 : * the full range at once. This means SimpleLruTruncate() can't trivially be
2876 : * used - instead the to-be-deleted range is computed using the offsets
2877 : * SLRU. C.f. TruncateMultiXact().
2878 : */
2879 : static void
2880 0 : PerformMembersTruncation(MultiXactOffset oldestOffset, MultiXactOffset newOldestOffset)
2881 : {
2882 0 : const int maxsegment = MXOffsetToMemberSegment(MaxMultiXactOffset);
2883 0 : int startsegment = MXOffsetToMemberSegment(oldestOffset);
2884 0 : int endsegment = MXOffsetToMemberSegment(newOldestOffset);
2885 0 : int segment = startsegment;
2886 :
2887 : /*
2888 : * Delete all the segments but the last one. The last segment can still
2889 : * contain, possibly partially, valid data.
2890 : */
2891 0 : while (segment != endsegment)
2892 : {
2893 0 : elog(DEBUG2, "truncating multixact members segment %x", segment);
2894 0 : SlruDeleteSegment(MultiXactMemberCtl, segment);
2895 :
2896 : /* move to next segment, handling wraparound correctly */
2897 0 : if (segment == maxsegment)
2898 0 : segment = 0;
2899 : else
2900 0 : segment += 1;
2901 : }
2902 0 : }
2903 :
2904 : /*
2905 : * Delete offsets segments [oldest, newOldest)
2906 : */
2907 : static void
2908 0 : PerformOffsetsTruncation(MultiXactId oldestMulti, MultiXactId newOldestMulti)
2909 : {
2910 : /*
2911 : * We step back one multixact to avoid passing a cutoff page that hasn't
2912 : * been created yet in the rare case that oldestMulti would be the first
2913 : * item on a page and oldestMulti == nextMulti. In that case, if we
2914 : * didn't subtract one, we'd trigger SimpleLruTruncate's wraparound
2915 : * detection.
2916 : */
2917 0 : SimpleLruTruncate(MultiXactOffsetCtl,
2918 0 : MultiXactIdToOffsetPage(PreviousMultiXactId(newOldestMulti)));
2919 0 : }
2920 :
2921 : /*
2922 : * Remove all MultiXactOffset and MultiXactMember segments before the oldest
2923 : * ones still of interest.
2924 : *
2925 : * This is only called on a primary as part of vacuum (via
2926 : * vac_truncate_clog()). During recovery truncation is done by replaying
2927 : * truncation WAL records logged here.
2928 : *
2929 : * newOldestMulti is the oldest currently required multixact, newOldestMultiDB
2930 : * is one of the databases preventing newOldestMulti from increasing.
2931 : */
2932 : void
2933 2 : TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB)
2934 : {
2935 : MultiXactId oldestMulti;
2936 : MultiXactId nextMulti;
2937 : MultiXactOffset newOldestOffset;
2938 : MultiXactOffset oldestOffset;
2939 : MultiXactOffset nextOffset;
2940 : mxtruncinfo trunc;
2941 : MultiXactId earliest;
2942 :
2943 2 : Assert(!RecoveryInProgress());
2944 2 : Assert(MultiXactState->finishedStartup);
2945 :
2946 : /*
2947 : * We can only allow one truncation to happen at once. Otherwise parts of
2948 : * members might vanish while we're doing lookups or similar. There's no
2949 : * need to have an interlock with creating new multis or such, since those
2950 : * are constrained by the limits (which only grow, never shrink).
2951 : */
2952 2 : LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
2953 :
2954 2 : LWLockAcquire(MultiXactGenLock, LW_SHARED);
2955 2 : nextMulti = MultiXactState->nextMXact;
2956 2 : nextOffset = MultiXactState->nextOffset;
2957 2 : oldestMulti = MultiXactState->oldestMultiXactId;
2958 2 : LWLockRelease(MultiXactGenLock);
2959 2 : Assert(MultiXactIdIsValid(oldestMulti));
2960 :
2961 : /*
2962 : * Make sure to only attempt truncation if there's values to truncate
2963 : * away. In normal processing values shouldn't go backwards, but there's
2964 : * some corner cases (due to bugs) where that's possible.
2965 : */
2966 2 : if (MultiXactIdPrecedesOrEquals(newOldestMulti, oldestMulti))
2967 : {
2968 2 : LWLockRelease(MultiXactTruncationLock);
2969 2 : return;
2970 : }
2971 :
2972 : /*
2973 : * Note we can't just plow ahead with the truncation; it's possible that
2974 : * there are no segments to truncate, which is a problem because we are
2975 : * going to attempt to read the offsets page to determine where to
2976 : * truncate the members SLRU. So we first scan the directory to determine
2977 : * the earliest offsets page number that we can read without error.
2978 : *
2979 : * NB: It's also possible that the page that oldestMulti is on has already
2980 : * been truncated away, and we crashed before updating oldestMulti.
2981 : */
2982 0 : trunc.earliestExistingPage = -1;
2983 0 : SlruScanDirectory(MultiXactOffsetCtl, SlruScanDirCbFindEarliest, &trunc);
2984 0 : earliest = trunc.earliestExistingPage * MULTIXACT_OFFSETS_PER_PAGE;
2985 0 : if (earliest < FirstMultiXactId)
2986 0 : earliest = FirstMultiXactId;
2987 :
2988 : /* If there's nothing to remove, we can bail out early. */
2989 0 : if (MultiXactIdPrecedes(oldestMulti, earliest))
2990 : {
2991 0 : LWLockRelease(MultiXactTruncationLock);
2992 0 : return;
2993 : }
2994 :
2995 : /*
2996 : * First, compute the safe truncation point for MultiXactMember. This is
2997 : * the starting offset of the oldest multixact.
2998 : *
2999 : * Hopefully, find_multixact_start will always work here, because we've
3000 : * already checked that it doesn't precede the earliest MultiXact on disk.
3001 : * But if it fails, don't truncate anything, and log a message.
3002 : */
3003 0 : if (oldestMulti == nextMulti)
3004 : {
3005 : /* there are NO MultiXacts */
3006 0 : oldestOffset = nextOffset;
3007 : }
3008 0 : else if (!find_multixact_start(oldestMulti, &oldestOffset))
3009 : {
3010 0 : ereport(LOG,
3011 : (errmsg("oldest MultiXact %u not found, earliest MultiXact %u, skipping truncation",
3012 : oldestMulti, earliest)));
3013 0 : LWLockRelease(MultiXactTruncationLock);
3014 0 : return;
3015 : }
3016 :
3017 : /*
3018 : * Secondly compute up to where to truncate. Lookup the corresponding
3019 : * member offset for newOldestMulti for that.
3020 : */
3021 0 : if (newOldestMulti == nextMulti)
3022 : {
3023 : /* there are NO MultiXacts */
3024 0 : newOldestOffset = nextOffset;
3025 : }
3026 0 : else if (!find_multixact_start(newOldestMulti, &newOldestOffset))
3027 : {
3028 0 : ereport(LOG,
3029 : (errmsg("cannot truncate up to MultiXact %u because it does not exist on disk, skipping truncation",
3030 : newOldestMulti)));
3031 0 : LWLockRelease(MultiXactTruncationLock);
3032 0 : return;
3033 : }
3034 :
3035 0 : elog(DEBUG1, "performing multixact truncation: "
3036 : "offsets [%u, %u), offsets segments [%x, %x), "
3037 : "members [%u, %u), members segments [%x, %x)",
3038 : oldestMulti, newOldestMulti,
3039 : MultiXactIdToOffsetSegment(oldestMulti),
3040 : MultiXactIdToOffsetSegment(newOldestMulti),
3041 : oldestOffset, newOldestOffset,
3042 : MXOffsetToMemberSegment(oldestOffset),
3043 : MXOffsetToMemberSegment(newOldestOffset));
3044 :
3045 : /*
3046 : * Do truncation, and the WAL logging of the truncation, in a critical
3047 : * section. That way offsets/members cannot get out of sync anymore, i.e.
3048 : * once consistent the newOldestMulti will always exist in members, even
3049 : * if we crashed in the wrong moment.
3050 : */
3051 0 : START_CRIT_SECTION();
3052 :
3053 : /*
3054 : * Prevent checkpoints from being scheduled concurrently. This is critical
3055 : * because otherwise a truncation record might not be replayed after a
3056 : * crash/basebackup, even though the state of the data directory would
3057 : * require it.
3058 : */
3059 0 : Assert(!MyPgXact->delayChkpt);
3060 0 : MyPgXact->delayChkpt = true;
3061 :
3062 : /* WAL log truncation */
3063 0 : WriteMTruncateXlogRec(newOldestMultiDB,
3064 : oldestMulti, newOldestMulti,
3065 : oldestOffset, newOldestOffset);
3066 :
3067 : /*
3068 : * Update in-memory limits before performing the truncation, while inside
3069 : * the critical section: Have to do it before truncation, to prevent
3070 : * concurrent lookups of those values. Has to be inside the critical
3071 : * section as otherwise a future call to this function would error out,
3072 : * while looking up the oldest member in offsets, if our caller crashes
3073 : * before updating the limits.
3074 : */
3075 0 : LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
3076 0 : MultiXactState->oldestMultiXactId = newOldestMulti;
3077 0 : MultiXactState->oldestMultiXactDB = newOldestMultiDB;
3078 0 : LWLockRelease(MultiXactGenLock);
3079 :
3080 : /* First truncate members */
3081 0 : PerformMembersTruncation(oldestOffset, newOldestOffset);
3082 :
3083 : /* Then offsets */
3084 0 : PerformOffsetsTruncation(oldestMulti, newOldestMulti);
3085 :
3086 0 : MyPgXact->delayChkpt = false;
3087 :
3088 0 : END_CRIT_SECTION();
3089 0 : LWLockRelease(MultiXactTruncationLock);
3090 : }
3091 :
3092 : /*
3093 : * Decide which of two MultiXactOffset page numbers is "older" for truncation
3094 : * purposes.
3095 : *
3096 : * We need to use comparison of MultiXactId here in order to do the right
3097 : * thing with wraparound. However, if we are asked about page number zero, we
3098 : * don't want to hand InvalidMultiXactId to MultiXactIdPrecedes: it'll get
3099 : * weird. So, offset both multis by FirstMultiXactId to avoid that.
3100 : * (Actually, the current implementation doesn't do anything weird with
3101 : * InvalidMultiXactId, but there's no harm in leaving this code like this.)
3102 : */
3103 : static bool
3104 0 : MultiXactOffsetPagePrecedes(int page1, int page2)
3105 : {
3106 : MultiXactId multi1;
3107 : MultiXactId multi2;
3108 :
3109 0 : multi1 = ((MultiXactId) page1) * MULTIXACT_OFFSETS_PER_PAGE;
3110 0 : multi1 += FirstMultiXactId;
3111 0 : multi2 = ((MultiXactId) page2) * MULTIXACT_OFFSETS_PER_PAGE;
3112 0 : multi2 += FirstMultiXactId;
3113 :
3114 0 : return MultiXactIdPrecedes(multi1, multi2);
3115 : }
3116 :
3117 : /*
3118 : * Decide which of two MultiXactMember page numbers is "older" for truncation
3119 : * purposes. There is no "invalid offset number" so use the numbers verbatim.
3120 : */
3121 : static bool
3122 0 : MultiXactMemberPagePrecedes(int page1, int page2)
3123 : {
3124 : MultiXactOffset offset1;
3125 : MultiXactOffset offset2;
3126 :
3127 0 : offset1 = ((MultiXactOffset) page1) * MULTIXACT_MEMBERS_PER_PAGE;
3128 0 : offset2 = ((MultiXactOffset) page2) * MULTIXACT_MEMBERS_PER_PAGE;
3129 :
3130 0 : return MultiXactOffsetPrecedes(offset1, offset2);
3131 : }
3132 :
3133 : /*
3134 : * Decide which of two MultiXactIds is earlier.
3135 : *
3136 : * XXX do we need to do something special for InvalidMultiXactId?
3137 : * (Doesn't look like it.)
3138 : */
3139 : bool
3140 25683 : MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2)
3141 : {
3142 25683 : int32 diff = (int32) (multi1 - multi2);
3143 :
3144 25683 : return (diff < 0);
3145 : }
3146 :
3147 : /*
3148 : * MultiXactIdPrecedesOrEquals -- is multi1 logically <= multi2?
3149 : *
3150 : * XXX do we need to do something special for InvalidMultiXactId?
3151 : * (Doesn't look like it.)
3152 : */
3153 : bool
3154 386 : MultiXactIdPrecedesOrEquals(MultiXactId multi1, MultiXactId multi2)
3155 : {
3156 386 : int32 diff = (int32) (multi1 - multi2);
3157 :
3158 386 : return (diff <= 0);
3159 : }
3160 :
3161 :
3162 : /*
3163 : * Decide which of two offsets is earlier.
3164 : */
3165 : static bool
3166 0 : MultiXactOffsetPrecedes(MultiXactOffset offset1, MultiXactOffset offset2)
3167 : {
3168 0 : int32 diff = (int32) (offset1 - offset2);
3169 :
3170 0 : return (diff < 0);
3171 : }
3172 :
3173 : /*
3174 : * Write an xlog record reflecting the zeroing of either a MEMBERs or
3175 : * OFFSETs page (info shows which)
3176 : */
3177 : static void
3178 2 : WriteMZeroPageXlogRec(int pageno, uint8 info)
3179 : {
3180 2 : XLogBeginInsert();
3181 2 : XLogRegisterData((char *) (&pageno), sizeof(int));
3182 2 : (void) XLogInsert(RM_MULTIXACT_ID, info);
3183 2 : }
3184 :
3185 : /*
3186 : * Write a TRUNCATE xlog record
3187 : *
3188 : * We must flush the xlog record to disk before returning --- see notes in
3189 : * TruncateCLOG().
3190 : */
3191 : static void
3192 0 : WriteMTruncateXlogRec(Oid oldestMultiDB,
3193 : MultiXactId startTruncOff, MultiXactId endTruncOff,
3194 : MultiXactOffset startTruncMemb, MultiXactOffset endTruncMemb)
3195 : {
3196 : XLogRecPtr recptr;
3197 : xl_multixact_truncate xlrec;
3198 :
3199 0 : xlrec.oldestMultiDB = oldestMultiDB;
3200 :
3201 0 : xlrec.startTruncOff = startTruncOff;
3202 0 : xlrec.endTruncOff = endTruncOff;
3203 :
3204 0 : xlrec.startTruncMemb = startTruncMemb;
3205 0 : xlrec.endTruncMemb = endTruncMemb;
3206 :
3207 0 : XLogBeginInsert();
3208 0 : XLogRegisterData((char *) (&xlrec), SizeOfMultiXactTruncate);
3209 0 : recptr = XLogInsert(RM_MULTIXACT_ID, XLOG_MULTIXACT_TRUNCATE_ID);
3210 0 : XLogFlush(recptr);
3211 0 : }
3212 :
3213 : /*
3214 : * MULTIXACT resource manager's routines
3215 : */
3216 : void
3217 0 : multixact_redo(XLogReaderState *record)
3218 : {
3219 0 : uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
3220 :
3221 : /* Backup blocks are not used in multixact records */
3222 0 : Assert(!XLogRecHasAnyBlockRefs(record));
3223 :
3224 0 : if (info == XLOG_MULTIXACT_ZERO_OFF_PAGE)
3225 : {
3226 : int pageno;
3227 : int slotno;
3228 :
3229 0 : memcpy(&pageno, XLogRecGetData(record), sizeof(int));
3230 :
3231 0 : LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
3232 :
3233 0 : slotno = ZeroMultiXactOffsetPage(pageno, false);
3234 0 : SimpleLruWritePage(MultiXactOffsetCtl, slotno);
3235 0 : Assert(!MultiXactOffsetCtl->shared->page_dirty[slotno]);
3236 :
3237 0 : LWLockRelease(MultiXactOffsetControlLock);
3238 : }
3239 0 : else if (info == XLOG_MULTIXACT_ZERO_MEM_PAGE)
3240 : {
3241 : int pageno;
3242 : int slotno;
3243 :
3244 0 : memcpy(&pageno, XLogRecGetData(record), sizeof(int));
3245 :
3246 0 : LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
3247 :
3248 0 : slotno = ZeroMultiXactMemberPage(pageno, false);
3249 0 : SimpleLruWritePage(MultiXactMemberCtl, slotno);
3250 0 : Assert(!MultiXactMemberCtl->shared->page_dirty[slotno]);
3251 :
3252 0 : LWLockRelease(MultiXactMemberControlLock);
3253 : }
3254 0 : else if (info == XLOG_MULTIXACT_CREATE_ID)
3255 : {
3256 0 : xl_multixact_create *xlrec =
3257 : (xl_multixact_create *) XLogRecGetData(record);
3258 : TransactionId max_xid;
3259 : int i;
3260 :
3261 : /* Store the data back into the SLRU files */
3262 0 : RecordNewMultiXact(xlrec->mid, xlrec->moff, xlrec->nmembers,
3263 0 : xlrec->members);
3264 :
3265 : /* Make sure nextMXact/nextOffset are beyond what this record has */
3266 0 : MultiXactAdvanceNextMXact(xlrec->mid + 1,
3267 0 : xlrec->moff + xlrec->nmembers);
3268 :
3269 : /*
3270 : * Make sure nextXid is beyond any XID mentioned in the record. This
3271 : * should be unnecessary, since any XID found here ought to have other
3272 : * evidence in the XLOG, but let's be safe.
3273 : */
3274 0 : max_xid = XLogRecGetXid(record);
3275 0 : for (i = 0; i < xlrec->nmembers; i++)
3276 : {
3277 0 : if (TransactionIdPrecedes(max_xid, xlrec->members[i].xid))
3278 0 : max_xid = xlrec->members[i].xid;
3279 : }
3280 :
3281 : /*
3282 : * We don't expect anyone else to modify nextXid, hence startup
3283 : * process doesn't need to hold a lock while checking this. We still
3284 : * acquire the lock to modify it, though.
3285 : */
3286 0 : if (TransactionIdFollowsOrEquals(max_xid,
3287 0 : ShmemVariableCache->nextXid))
3288 : {
3289 0 : LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
3290 0 : ShmemVariableCache->nextXid = max_xid;
3291 0 : TransactionIdAdvance(ShmemVariableCache->nextXid);
3292 0 : LWLockRelease(XidGenLock);
3293 : }
3294 : }
3295 0 : else if (info == XLOG_MULTIXACT_TRUNCATE_ID)
3296 : {
3297 : xl_multixact_truncate xlrec;
3298 : int pageno;
3299 :
3300 0 : memcpy(&xlrec, XLogRecGetData(record),
3301 : SizeOfMultiXactTruncate);
3302 :
3303 0 : elog(DEBUG1, "replaying multixact truncation: "
3304 : "offsets [%u, %u), offsets segments [%x, %x), "
3305 : "members [%u, %u), members segments [%x, %x)",
3306 : xlrec.startTruncOff, xlrec.endTruncOff,
3307 : MultiXactIdToOffsetSegment(xlrec.startTruncOff),
3308 : MultiXactIdToOffsetSegment(xlrec.endTruncOff),
3309 : xlrec.startTruncMemb, xlrec.endTruncMemb,
3310 : MXOffsetToMemberSegment(xlrec.startTruncMemb),
3311 : MXOffsetToMemberSegment(xlrec.endTruncMemb));
3312 :
3313 : /* should not be required, but more than cheap enough */
3314 0 : LWLockAcquire(MultiXactTruncationLock, LW_EXCLUSIVE);
3315 :
3316 : /*
3317 : * Advance the horizon values, so they're current at the end of
3318 : * recovery.
3319 : */
3320 0 : SetMultiXactIdLimit(xlrec.endTruncOff, xlrec.oldestMultiDB, false);
3321 :
3322 0 : PerformMembersTruncation(xlrec.startTruncMemb, xlrec.endTruncMemb);
3323 :
3324 : /*
3325 : * During XLOG replay, latest_page_number isn't necessarily set up
3326 : * yet; insert a suitable value to bypass the sanity test in
3327 : * SimpleLruTruncate.
3328 : */
3329 0 : pageno = MultiXactIdToOffsetPage(xlrec.endTruncOff);
3330 0 : MultiXactOffsetCtl->shared->latest_page_number = pageno;
3331 0 : PerformOffsetsTruncation(xlrec.startTruncOff, xlrec.endTruncOff);
3332 :
3333 0 : LWLockRelease(MultiXactTruncationLock);
3334 : }
3335 : else
3336 0 : elog(PANIC, "multixact_redo: unknown op code %u", info);
3337 0 : }
3338 :
3339 : Datum
3340 0 : pg_get_multixact_members(PG_FUNCTION_ARGS)
3341 : {
3342 : typedef struct
3343 : {
3344 : MultiXactMember *members;
3345 : int nmembers;
3346 : int iter;
3347 : } mxact;
3348 0 : MultiXactId mxid = PG_GETARG_UINT32(0);
3349 : mxact *multi;
3350 : FuncCallContext *funccxt;
3351 :
3352 0 : if (mxid < FirstMultiXactId)
3353 0 : ereport(ERROR,
3354 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
3355 : errmsg("invalid MultiXactId: %u", mxid)));
3356 :
3357 0 : if (SRF_IS_FIRSTCALL())
3358 : {
3359 : MemoryContext oldcxt;
3360 : TupleDesc tupdesc;
3361 :
3362 0 : funccxt = SRF_FIRSTCALL_INIT();
3363 0 : oldcxt = MemoryContextSwitchTo(funccxt->multi_call_memory_ctx);
3364 :
3365 0 : multi = palloc(sizeof(mxact));
3366 : /* no need to allow for old values here */
3367 0 : multi->nmembers = GetMultiXactIdMembers(mxid, &multi->members, false,
3368 : false);
3369 0 : multi->iter = 0;
3370 :
3371 0 : tupdesc = CreateTemplateTupleDesc(2, false);
3372 0 : TupleDescInitEntry(tupdesc, (AttrNumber) 1, "xid",
3373 : XIDOID, -1, 0);
3374 0 : TupleDescInitEntry(tupdesc, (AttrNumber) 2, "mode",
3375 : TEXTOID, -1, 0);
3376 :
3377 0 : funccxt->attinmeta = TupleDescGetAttInMetadata(tupdesc);
3378 0 : funccxt->user_fctx = multi;
3379 :
3380 0 : MemoryContextSwitchTo(oldcxt);
3381 : }
3382 :
3383 0 : funccxt = SRF_PERCALL_SETUP();
3384 0 : multi = (mxact *) funccxt->user_fctx;
3385 :
3386 0 : while (multi->iter < multi->nmembers)
3387 : {
3388 : HeapTuple tuple;
3389 : char *values[2];
3390 :
3391 0 : values[0] = psprintf("%u", multi->members[multi->iter].xid);
3392 0 : values[1] = mxstatus_to_string(multi->members[multi->iter].status);
3393 :
3394 0 : tuple = BuildTupleFromCStrings(funccxt->attinmeta, values);
3395 :
3396 0 : multi->iter++;
3397 0 : pfree(values[0]);
3398 0 : SRF_RETURN_NEXT(funccxt, HeapTupleGetDatum(tuple));
3399 : }
3400 :
3401 0 : if (multi->nmembers > 0)
3402 0 : pfree(multi->members);
3403 0 : pfree(multi);
3404 :
3405 0 : SRF_RETURN_DONE(funccxt);
3406 : }
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