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) 2016-2024, 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     8889084 : mask_page_lsn_and_checksum(Page page)
      32             : {
      33     8889084 :     PageHeader  phdr = (PageHeader) page;
      34             : 
      35     8889084 :     PageXLogRecPtrSet(phdr->pd_lsn, (uint64) MASK_MARKER);
      36     8889084 :     phdr->pd_checksum = MASK_MARKER;
      37     8889084 : }
      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     8886792 : mask_page_hint_bits(Page page)
      47             : {
      48     8886792 :     PageHeader  phdr = (PageHeader) page;
      49             : 
      50             :     /* Ignore prune_xid (it's like a hint-bit) */
      51     8886792 :     phdr->pd_prune_xid = MASK_MARKER;
      52             : 
      53             :     /* Ignore PD_PAGE_FULL and PD_HAS_FREE_LINES flags, they are just hints. */
      54     8886792 :     PageClearFull(page);
      55     8886792 :     PageClearHasFreeLinePointers(page);
      56             : 
      57             :     /*
      58             :      * During replay, if the page LSN has advanced past our XLOG record's LSN,
      59             :      * we don't mark the page all-visible. See heap_xlog_visible() for
      60             :      * details.
      61             :      */
      62     8886792 :     PageClearAllVisible(page);
      63     8886792 : }
      64             : 
      65             : /*
      66             :  * mask_unused_space
      67             :  *
      68             :  * Mask the unused space of a page between pd_lower and pd_upper.
      69             :  */
      70             : void
      71     8886484 : mask_unused_space(Page page)
      72             : {
      73     8886484 :     int         pd_lower = ((PageHeader) page)->pd_lower;
      74     8886484 :     int         pd_upper = ((PageHeader) page)->pd_upper;
      75     8886484 :     int         pd_special = ((PageHeader) page)->pd_special;
      76             : 
      77             :     /* Sanity check */
      78     8886484 :     if (pd_lower > pd_upper || pd_special < pd_upper ||
      79     8886484 :         pd_lower < SizeOfPageHeaderData || pd_special > BLCKSZ)
      80             :     {
      81           0 :         elog(ERROR, "invalid page pd_lower %u pd_upper %u pd_special %u",
      82             :              pd_lower, pd_upper, pd_special);
      83             :     }
      84             : 
      85     8886484 :     memset(page + pd_lower, MASK_MARKER, pd_upper - pd_lower);
      86     8886484 : }
      87             : 
      88             : /*
      89             :  * mask_lp_flags
      90             :  *
      91             :  * In some index AMs, line pointer flags can be modified on the primary
      92             :  * without emitting any WAL record.
      93             :  */
      94             : void
      95     2252316 : mask_lp_flags(Page page)
      96             : {
      97             :     OffsetNumber offnum,
      98             :                 maxoff;
      99             : 
     100     2252316 :     maxoff = PageGetMaxOffsetNumber(page);
     101   396274468 :     for (offnum = FirstOffsetNumber;
     102             :          offnum <= maxoff;
     103   394022152 :          offnum = OffsetNumberNext(offnum))
     104             :     {
     105   394022152 :         ItemId      itemId = PageGetItemId(page, offnum);
     106             : 
     107   394022152 :         if (ItemIdIsUsed(itemId))
     108   394017392 :             itemId->lp_flags = LP_UNUSED;
     109             :     }
     110     2252316 : }
     111             : 
     112             : /*
     113             :  * mask_page_content
     114             :  *
     115             :  * In some index AMs, the contents of deleted pages need to be almost
     116             :  * completely ignored.
     117             :  */
     118             : void
     119         712 : mask_page_content(Page page)
     120             : {
     121             :     /* Mask Page Content */
     122         712 :     memset(page + SizeOfPageHeaderData, MASK_MARKER,
     123             :            BLCKSZ - SizeOfPageHeaderData);
     124             : 
     125             :     /* Mask pd_lower and pd_upper */
     126         712 :     memset(&((PageHeader) page)->pd_lower, MASK_MARKER,
     127             :            sizeof(uint16));
     128         712 :     memset(&((PageHeader) page)->pd_upper, MASK_MARKER,
     129             :            sizeof(uint16));
     130         712 : }