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) 2016-2026, PostgreSQL Global Development Group
       9              :  *
      10              :  * Contains common routines required for masking a page.
      11              :  *
      12              :  * IDENTIFICATION
      13              :  *    src/backend/access/common/bufmask.c
      14              :  *
      15              :  *-------------------------------------------------------------------------
      16              :  */
      17              : 
      18              : #include "postgres.h"
      19              : 
      20              : #include "access/bufmask.h"
      21              : 
      22              : /*
      23              :  * mask_page_lsn_and_checksum
      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 and
      27              :  * the state of the page when WAL is applied. Also, mask out checksum as
      28              :  * masking anything else on page means checksum is not going to match as well.
      29              :  */
      30              : void
      31      4802406 : mask_page_lsn_and_checksum(Page page)
      32              : {
      33      4802406 :     PageHeader  phdr = (PageHeader) page;
      34              : 
      35      4802406 :     PageXLogRecPtrSet(&phdr->pd_lsn, (uint64) MASK_MARKER);
      36      4802406 :     phdr->pd_checksum = MASK_MARKER;
      37      4802406 : }
      38              : 
      39              : /*
      40              :  * mask_page_hint_bits
      41              :  *
      42              :  * Mask hint bits in PageHeader. We want to ignore differences in hint bits,
      43              :  * since they can be set without emitting any WAL.
      44              :  */
      45              : void
      46      4801186 : mask_page_hint_bits(Page page)
      47              : {
      48      4801186 :     PageHeader  phdr = (PageHeader) page;
      49              : 
      50              :     /* Ignore prune_xid (it's like a hint-bit) */
      51      4801186 :     phdr->pd_prune_xid = MASK_MARKER;
      52              : 
      53              :     /* Ignore PD_PAGE_FULL and PD_HAS_FREE_LINES flags, they are just hints. */
      54      4801186 :     PageClearFull(page);
      55      4801186 :     PageClearHasFreeLinePointers(page);
      56              : 
      57              :     /*
      58              :      * PD_ALL_VISIBLE is masked during WAL consistency checking. XXX: It is
      59              :      * worth investigating if we could stop doing this.
      60              :      */
      61      4801186 :     PageClearAllVisible(page);
      62      4801186 : }
      63              : 
      64              : /*
      65              :  * mask_unused_space
      66              :  *
      67              :  * Mask the unused space of a page between pd_lower and pd_upper.
      68              :  */
      69              : void
      70      4801110 : mask_unused_space(Page page)
      71              : {
      72      4801110 :     int         pd_lower = ((PageHeader) page)->pd_lower;
      73      4801110 :     int         pd_upper = ((PageHeader) page)->pd_upper;
      74      4801110 :     int         pd_special = ((PageHeader) page)->pd_special;
      75              : 
      76              :     /* Sanity check */
      77      4801110 :     if (pd_lower > pd_upper || pd_special < pd_upper ||
      78      4801110 :         pd_lower < SizeOfPageHeaderData || pd_special > BLCKSZ)
      79              :     {
      80            0 :         elog(ERROR, "invalid page pd_lower %u pd_upper %u pd_special %u",
      81              :              pd_lower, pd_upper, pd_special);
      82              :     }
      83              : 
      84      4801110 :     memset(page + pd_lower, MASK_MARKER, pd_upper - pd_lower);
      85      4801110 : }
      86              : 
      87              : /*
      88              :  * mask_lp_flags
      89              :  *
      90              :  * In some index AMs, line pointer flags can be modified on the primary
      91              :  * without emitting any WAL record.
      92              :  */
      93              : void
      94      1271046 : mask_lp_flags(Page page)
      95              : {
      96              :     OffsetNumber offnum,
      97              :                 maxoff;
      98              : 
      99      1271046 :     maxoff = PageGetMaxOffsetNumber(page);
     100      1271046 :     for (offnum = FirstOffsetNumber;
     101    226464582 :          offnum <= maxoff;
     102    225193536 :          offnum = OffsetNumberNext(offnum))
     103              :     {
     104    225193536 :         ItemId      itemId = PageGetItemId(page, offnum);
     105              : 
     106    225193536 :         if (ItemIdIsUsed(itemId))
     107    225190372 :             itemId->lp_flags = LP_UNUSED;
     108              :     }
     109      1271046 : }
     110              : 
     111              : /*
     112              :  * mask_page_content
     113              :  *
     114              :  * In some index AMs, the contents of deleted pages need to be almost
     115              :  * completely ignored.
     116              :  */
     117              : void
     118          356 : mask_page_content(Page page)
     119              : {
     120              :     /* Mask Page Content */
     121          356 :     memset(page + SizeOfPageHeaderData, MASK_MARKER,
     122              :            BLCKSZ - SizeOfPageHeaderData);
     123              : 
     124              :     /* Mask pd_lower and pd_upper */
     125          356 :     memset(&((PageHeader) page)->pd_lower, MASK_MARKER,
     126              :            sizeof(uint16));
     127          356 :     memset(&((PageHeader) page)->pd_upper, MASK_MARKER,
     128              :            sizeof(uint16));
     129          356 : }