Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * bufmask.c
       4             :  *    Routines for buffer masking. Used to mask certain bits
       5             :  *    in a page which can be different when the WAL is generated
       6             :  *    and when the WAL is applied.
       7             :  *
       8             :  * Portions Copyright (c) 2016-2017, PostgreSQL Global Development Group
       9             :  *
      10             :  * Contains common routines required for masking a page.
      11             :  *
      12             :  * IDENTIFICATION
      13             :  *    src/backend/storage/buffer/bufmask.c
      14             :  *
      15             :  *-------------------------------------------------------------------------
      16             :  */
      17             : 
      18             : #include "postgres.h"
      19             : 
      20             : #include "access/bufmask.h"
      21             : 
      22             : /*
      23             :  * mask_page_lsn
      24             :  *
      25             :  * In consistency checks, the LSN of the two pages compared will likely be
      26             :  * different because of concurrent operations when the WAL is generated
      27             :  * and the state of the page when WAL is applied.
      28             :  */
      29             : void
      30           0 : mask_page_lsn(Page page)
      31             : {
      32           0 :     PageHeader  phdr = (PageHeader) page;
      33             : 
      34           0 :     PageXLogRecPtrSet(phdr->pd_lsn, (uint64) MASK_MARKER);
      35           0 : }
      36             : 
      37             : /*
      38             :  * mask_page_hint_bits
      39             :  *
      40             :  * Mask hint bits in PageHeader. We want to ignore differences in hint bits,
      41             :  * since they can be set without emitting any WAL.
      42             :  */
      43             : void
      44           0 : mask_page_hint_bits(Page page)
      45             : {
      46           0 :     PageHeader  phdr = (PageHeader) page;
      47             : 
      48             :     /* Ignore prune_xid (it's like a hint-bit) */
      49           0 :     phdr->pd_prune_xid = MASK_MARKER;
      50             : 
      51             :     /* Ignore PD_PAGE_FULL and PD_HAS_FREE_LINES flags, they are just hints. */
      52           0 :     PageClearFull(page);
      53           0 :     PageClearHasFreeLinePointers(page);
      54             : 
      55             :     /*
      56             :      * During replay, if the page LSN has advanced past our XLOG record's LSN,
      57             :      * we don't mark the page all-visible. See heap_xlog_visible() for
      58             :      * details.
      59             :      */
      60           0 :     PageClearAllVisible(page);
      61           0 : }
      62             : 
      63             : /*
      64             :  * mask_unused_space
      65             :  *
      66             :  * Mask the unused space of a page between pd_lower and pd_upper.
      67             :  */
      68             : void
      69           0 : mask_unused_space(Page page)
      70             : {
      71           0 :     int         pd_lower = ((PageHeader) page)->pd_lower;
      72           0 :     int         pd_upper = ((PageHeader) page)->pd_upper;
      73           0 :     int         pd_special = ((PageHeader) page)->pd_special;
      74             : 
      75             :     /* Sanity check */
      76           0 :     if (pd_lower > pd_upper || pd_special < pd_upper ||
      77           0 :         pd_lower < SizeOfPageHeaderData || pd_special > BLCKSZ)
      78             :     {
      79           0 :         elog(ERROR, "invalid page pd_lower %u pd_upper %u pd_special %u\n",
      80             :              pd_lower, pd_upper, pd_special);
      81             :     }
      82             : 
      83           0 :     memset(page + pd_lower, MASK_MARKER, pd_upper - pd_lower);
      84           0 : }
      85             : 
      86             : /*
      87             :  * mask_lp_flags
      88             :  *
      89             :  * In some index AMs, line pointer flags can be modified in master without
      90             :  * emitting any WAL record.
      91             :  */
      92             : void
      93           0 : mask_lp_flags(Page page)
      94             : {
      95             :     OffsetNumber offnum,
      96             :                 maxoff;
      97             : 
      98           0 :     maxoff = PageGetMaxOffsetNumber(page);
      99           0 :     for (offnum = FirstOffsetNumber;
     100             :          offnum <= maxoff;
     101           0 :          offnum = OffsetNumberNext(offnum))
     102             :     {
     103           0 :         ItemId      itemId = PageGetItemId(page, offnum);
     104             : 
     105           0 :         if (ItemIdIsUsed(itemId))
     106           0 :             itemId->lp_flags = LP_UNUSED;
     107             :     }
     108           0 : }
     109             : 
     110             : /*
     111             :  * mask_page_content
     112             :  *
     113             :  * In some index AMs, the contents of deleted pages need to be almost
     114             :  * completely ignored.
     115             :  */
     116             : void
     117           0 : mask_page_content(Page page)
     118             : {
     119             :     /* Mask Page Content */
     120           0 :     memset(page + SizeOfPageHeaderData, MASK_MARKER,
     121             :            BLCKSZ - SizeOfPageHeaderData);
     122             : 
     123             :     /* Mask pd_lower and pd_upper */
     124           0 :     memset(&((PageHeader) page)->pd_lower, MASK_MARKER,
     125             :            sizeof(uint16));
     126           0 :     memset(&((PageHeader) page)->pd_upper, MASK_MARKER,
     127             :            sizeof(uint16));
     128           0 : }