Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * evtcache.c
4 : * Special-purpose cache for event trigger data.
5 : *
6 : * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
7 : * Portions Copyright (c) 1994, Regents of the University of California
8 : *
9 : * IDENTIFICATION
10 : * src/backend/utils/cache/evtcache.c
11 : *
12 : *-------------------------------------------------------------------------
13 : */
14 : #include "postgres.h"
15 :
16 : #include "access/genam.h"
17 : #include "access/heapam.h"
18 : #include "access/htup_details.h"
19 : #include "catalog/pg_event_trigger.h"
20 : #include "catalog/indexing.h"
21 : #include "catalog/pg_type.h"
22 : #include "commands/trigger.h"
23 : #include "utils/array.h"
24 : #include "utils/builtins.h"
25 : #include "utils/catcache.h"
26 : #include "utils/evtcache.h"
27 : #include "utils/inval.h"
28 : #include "utils/memutils.h"
29 : #include "utils/hsearch.h"
30 : #include "utils/rel.h"
31 : #include "utils/snapmgr.h"
32 : #include "utils/syscache.h"
33 :
34 : typedef enum
35 : {
36 : ETCS_NEEDS_REBUILD,
37 : ETCS_REBUILD_STARTED,
38 : ETCS_VALID
39 : } EventTriggerCacheStateType;
40 :
41 : typedef struct
42 : {
43 : EventTriggerEvent event;
44 : List *triggerlist;
45 : } EventTriggerCacheEntry;
46 :
47 : static HTAB *EventTriggerCache;
48 : static MemoryContext EventTriggerCacheContext;
49 : static EventTriggerCacheStateType EventTriggerCacheState = ETCS_NEEDS_REBUILD;
50 :
51 : static void BuildEventTriggerCache(void);
52 : static void InvalidateEventCacheCallback(Datum arg,
53 : int cacheid, uint32 hashvalue);
54 : static int DecodeTextArrayToCString(Datum array, char ***cstringp);
55 :
56 : /*
57 : * Search the event cache by trigger event.
58 : *
59 : * Note that the caller had better copy any data it wants to keep around
60 : * across any operation that might touch a system catalog into some other
61 : * memory context, since a cache reset could blow the return value away.
62 : */
63 : List *
64 42846 : EventCacheLookup(EventTriggerEvent event)
65 : {
66 : EventTriggerCacheEntry *entry;
67 :
68 42846 : if (EventTriggerCacheState != ETCS_VALID)
69 213 : BuildEventTriggerCache();
70 42846 : entry = hash_search(EventTriggerCache, &event, HASH_FIND, NULL);
71 42846 : return entry != NULL ? entry->triggerlist : NIL;
72 : }
73 :
74 : /*
75 : * Rebuild the event trigger cache.
76 : */
77 : static void
78 213 : BuildEventTriggerCache(void)
79 : {
80 : HASHCTL ctl;
81 : HTAB *cache;
82 : MemoryContext oldcontext;
83 : Relation rel;
84 : Relation irel;
85 : SysScanDesc scan;
86 :
87 213 : if (EventTriggerCacheContext != NULL)
88 : {
89 : /*
90 : * Free up any memory already allocated in EventTriggerCacheContext.
91 : * This can happen either because a previous rebuild failed, or
92 : * because an invalidation happened before the rebuild was complete.
93 : */
94 24 : MemoryContextResetAndDeleteChildren(EventTriggerCacheContext);
95 : }
96 : else
97 : {
98 : /*
99 : * This is our first time attempting to build the cache, so we need to
100 : * set up the memory context and register a syscache callback to
101 : * capture future invalidation events.
102 : */
103 189 : if (CacheMemoryContext == NULL)
104 0 : CreateCacheMemoryContext();
105 189 : EventTriggerCacheContext =
106 189 : AllocSetContextCreate(CacheMemoryContext,
107 : "EventTriggerCache",
108 : ALLOCSET_DEFAULT_SIZES);
109 189 : CacheRegisterSyscacheCallback(EVENTTRIGGEROID,
110 : InvalidateEventCacheCallback,
111 : (Datum) 0);
112 : }
113 :
114 : /* Switch to correct memory context. */
115 213 : oldcontext = MemoryContextSwitchTo(EventTriggerCacheContext);
116 :
117 : /* Prevent the memory context from being nuked while we're rebuilding. */
118 213 : EventTriggerCacheState = ETCS_REBUILD_STARTED;
119 :
120 : /* Create new hash table. */
121 213 : MemSet(&ctl, 0, sizeof(ctl));
122 213 : ctl.keysize = sizeof(EventTriggerEvent);
123 213 : ctl.entrysize = sizeof(EventTriggerCacheEntry);
124 213 : ctl.hcxt = EventTriggerCacheContext;
125 213 : cache = hash_create("Event Trigger Cache", 32, &ctl,
126 : HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
127 :
128 : /*
129 : * Prepare to scan pg_event_trigger in name order.
130 : */
131 213 : rel = relation_open(EventTriggerRelationId, AccessShareLock);
132 213 : irel = index_open(EventTriggerNameIndexId, AccessShareLock);
133 213 : scan = systable_beginscan_ordered(rel, irel, NULL, 0, NULL);
134 :
135 : /*
136 : * Build a cache item for each pg_event_trigger tuple, and append each one
137 : * to the appropriate cache entry.
138 : */
139 : for (;;)
140 : {
141 : HeapTuple tup;
142 : Form_pg_event_trigger form;
143 : char *evtevent;
144 : EventTriggerEvent event;
145 : EventTriggerCacheItem *item;
146 : Datum evttags;
147 : bool evttags_isnull;
148 : EventTriggerCacheEntry *entry;
149 : bool found;
150 :
151 : /* Get next tuple. */
152 234 : tup = systable_getnext_ordered(scan, ForwardScanDirection);
153 234 : if (!HeapTupleIsValid(tup))
154 213 : break;
155 :
156 : /* Skip trigger if disabled. */
157 21 : form = (Form_pg_event_trigger) GETSTRUCT(tup);
158 21 : if (form->evtenabled == TRIGGER_DISABLED)
159 6 : continue;
160 :
161 : /* Decode event name. */
162 18 : evtevent = NameStr(form->evtevent);
163 18 : if (strcmp(evtevent, "ddl_command_start") == 0)
164 3 : event = EVT_DDLCommandStart;
165 15 : else if (strcmp(evtevent, "ddl_command_end") == 0)
166 6 : event = EVT_DDLCommandEnd;
167 9 : else if (strcmp(evtevent, "sql_drop") == 0)
168 8 : event = EVT_SQLDrop;
169 1 : else if (strcmp(evtevent, "table_rewrite") == 0)
170 1 : event = EVT_TableRewrite;
171 : else
172 0 : continue;
173 :
174 : /* Allocate new cache item. */
175 18 : item = palloc0(sizeof(EventTriggerCacheItem));
176 18 : item->fnoid = form->evtfoid;
177 18 : item->enabled = form->evtenabled;
178 :
179 : /* Decode and sort tags array. */
180 18 : evttags = heap_getattr(tup, Anum_pg_event_trigger_evttags,
181 : RelationGetDescr(rel), &evttags_isnull);
182 18 : if (!evttags_isnull)
183 : {
184 9 : item->ntags = DecodeTextArrayToCString(evttags, &item->tag);
185 9 : qsort(item->tag, item->ntags, sizeof(char *), pg_qsort_strcmp);
186 : }
187 :
188 : /* Add to cache entry. */
189 18 : entry = hash_search(cache, &event, HASH_ENTER, &found);
190 18 : if (found)
191 1 : entry->triggerlist = lappend(entry->triggerlist, item);
192 : else
193 17 : entry->triggerlist = list_make1(item);
194 21 : }
195 :
196 : /* Done with pg_event_trigger scan. */
197 213 : systable_endscan_ordered(scan);
198 213 : index_close(irel, AccessShareLock);
199 213 : relation_close(rel, AccessShareLock);
200 :
201 : /* Restore previous memory context. */
202 213 : MemoryContextSwitchTo(oldcontext);
203 :
204 : /* Install new cache. */
205 213 : EventTriggerCache = cache;
206 :
207 : /*
208 : * If the cache has been invalidated since we entered this routine, we
209 : * still use and return the cache we just finished constructing, to avoid
210 : * infinite loops, but we leave the cache marked stale so that we'll
211 : * rebuild it again on next access. Otherwise, we mark the cache valid.
212 : */
213 213 : if (EventTriggerCacheState == ETCS_REBUILD_STARTED)
214 213 : EventTriggerCacheState = ETCS_VALID;
215 213 : }
216 :
217 : /*
218 : * Decode text[] to an array of C strings.
219 : *
220 : * We could avoid a bit of overhead here if we were willing to duplicate some
221 : * of the logic from deconstruct_array, but it doesn't seem worth the code
222 : * complexity.
223 : */
224 : static int
225 9 : DecodeTextArrayToCString(Datum array, char ***cstringp)
226 : {
227 9 : ArrayType *arr = DatumGetArrayTypeP(array);
228 : Datum *elems;
229 : char **cstring;
230 : int i;
231 : int nelems;
232 :
233 9 : if (ARR_NDIM(arr) != 1 || ARR_HASNULL(arr) || ARR_ELEMTYPE(arr) != TEXTOID)
234 0 : elog(ERROR, "expected 1-D text array");
235 9 : deconstruct_array(arr, TEXTOID, -1, false, 'i', &elems, NULL, &nelems);
236 :
237 9 : cstring = palloc(nelems * sizeof(char *));
238 31 : for (i = 0; i < nelems; ++i)
239 22 : cstring[i] = TextDatumGetCString(elems[i]);
240 :
241 9 : pfree(elems);
242 9 : *cstringp = cstring;
243 9 : return nelems;
244 : }
245 :
246 : /*
247 : * Flush all cache entries when pg_event_trigger is updated.
248 : *
249 : * This should be rare enough that we don't need to be very granular about
250 : * it, so we just blow away everything, which also avoids the possibility of
251 : * memory leaks.
252 : */
253 : static void
254 46 : InvalidateEventCacheCallback(Datum arg, int cacheid, uint32 hashvalue)
255 : {
256 : /*
257 : * If the cache isn't valid, then there might be a rebuild in progress, so
258 : * we can't immediately blow it away. But it's advantageous to do this
259 : * when possible, so as to immediately free memory.
260 : */
261 46 : if (EventTriggerCacheState == ETCS_VALID)
262 : {
263 26 : MemoryContextResetAndDeleteChildren(EventTriggerCacheContext);
264 26 : EventTriggerCache = NULL;
265 : }
266 :
267 : /* Mark cache for rebuild. */
268 46 : EventTriggerCacheState = ETCS_NEEDS_REBUILD;
269 46 : }
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