TLA  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) 2016-2023, 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 UBC           0 : mask_page_lsn_and_checksum(Page page)
      32                 : {
      33               0 :     PageHeader  phdr = (PageHeader) page;
      34                 : 
      35               0 :     PageXLogRecPtrSet(phdr->pd_lsn, (uint64) MASK_MARKER);
      36               0 :     phdr->pd_checksum = MASK_MARKER;
      37               0 : }
      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               0 : mask_page_hint_bits(Page page)
      47                 : {
      48               0 :     PageHeader  phdr = (PageHeader) page;
      49                 : 
      50                 :     /* Ignore prune_xid (it's like a hint-bit) */
      51               0 :     phdr->pd_prune_xid = MASK_MARKER;
      52                 : 
      53                 :     /* Ignore PD_PAGE_FULL and PD_HAS_FREE_LINES flags, they are just hints. */
      54               0 :     PageClearFull(page);
      55               0 :     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               0 :     PageClearAllVisible(page);
      63               0 : }
      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               0 : mask_unused_space(Page page)
      72                 : {
      73               0 :     int         pd_lower = ((PageHeader) page)->pd_lower;
      74               0 :     int         pd_upper = ((PageHeader) page)->pd_upper;
      75               0 :     int         pd_special = ((PageHeader) page)->pd_special;
      76                 : 
      77                 :     /* Sanity check */
      78               0 :     if (pd_lower > pd_upper || pd_special < pd_upper ||
      79               0 :         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               0 :     memset(page + pd_lower, MASK_MARKER, pd_upper - pd_lower);
      86               0 : }
      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               0 : mask_lp_flags(Page page)
      96                 : {
      97                 :     OffsetNumber offnum,
      98                 :                 maxoff;
      99                 : 
     100               0 :     maxoff = PageGetMaxOffsetNumber(page);
     101               0 :     for (offnum = FirstOffsetNumber;
     102               0 :          offnum <= maxoff;
     103               0 :          offnum = OffsetNumberNext(offnum))
     104                 :     {
     105               0 :         ItemId      itemId = PageGetItemId(page, offnum);
     106                 : 
     107               0 :         if (ItemIdIsUsed(itemId))
     108               0 :             itemId->lp_flags = LP_UNUSED;
     109                 :     }
     110               0 : }
     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               0 : mask_page_content(Page page)
     120                 : {
     121                 :     /* Mask Page Content */
     122               0 :     memset(page + SizeOfPageHeaderData, MASK_MARKER,
     123                 :            BLCKSZ - SizeOfPageHeaderData);
     124                 : 
     125                 :     /* Mask pd_lower and pd_upper */
     126               0 :     memset(&((PageHeader) page)->pd_lower, MASK_MARKER,
     127                 :            sizeof(uint16));
     128               0 :     memset(&((PageHeader) page)->pd_upper, MASK_MARKER,
     129                 :            sizeof(uint16));
     130               0 : }