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/*-------------------------------------------------------------------------
*
* bufmask.c
* Routines for buffer masking. Used to mask certain bits
* in a page which can be different when the WAL is generated
* and when the WAL is applied.
*
* Portions Copyright (c) 2016-2023, PostgreSQL Global Development Group
*
* Contains common routines required for masking a page.
*
* IDENTIFICATION
* src/backend/access/common/bufmask.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/bufmask.h"
/*
* mask_page_lsn_and_checksum
*
* In consistency checks, the LSN of the two pages compared will likely be
* different because of concurrent operations when the WAL is generated and
* the state of the page when WAL is applied. Also, mask out checksum as
* masking anything else on page means checksum is not going to match as well.
*/
void
mask_page_lsn_and_checksum(Page page)
{
PageHeader phdr = (PageHeader) page;
PageXLogRecPtrSet(phdr->pd_lsn, (uint64) MASK_MARKER);
phdr->pd_checksum = MASK_MARKER;
}
/*
* mask_page_hint_bits
*
* Mask hint bits in PageHeader. We want to ignore differences in hint bits,
* since they can be set without emitting any WAL.
*/
void
mask_page_hint_bits(Page page)
{
PageHeader phdr = (PageHeader) page;
/* Ignore prune_xid (it's like a hint-bit) */
phdr->pd_prune_xid = MASK_MARKER;
/* Ignore PD_PAGE_FULL and PD_HAS_FREE_LINES flags, they are just hints. */
PageClearFull(page);
PageClearHasFreeLinePointers(page);
/*
* During replay, if the page LSN has advanced past our XLOG record's LSN,
* we don't mark the page all-visible. See heap_xlog_visible() for
* details.
*/
PageClearAllVisible(page);
}
/*
* mask_unused_space
*
* Mask the unused space of a page between pd_lower and pd_upper.
*/
void
mask_unused_space(Page page)
{
int pd_lower = ((PageHeader) page)->pd_lower;
int pd_upper = ((PageHeader) page)->pd_upper;
int pd_special = ((PageHeader) page)->pd_special;
/* Sanity check */
if (pd_lower > pd_upper || pd_special < pd_upper ||
pd_lower < SizeOfPageHeaderData || pd_special > BLCKSZ)
{
elog(ERROR, "invalid page pd_lower %u pd_upper %u pd_special %u",
pd_lower, pd_upper, pd_special);
}
memset(page + pd_lower, MASK_MARKER, pd_upper - pd_lower);
}
/*
* mask_lp_flags
*
* In some index AMs, line pointer flags can be modified on the primary
* without emitting any WAL record.
*/
void
mask_lp_flags(Page page)
{
OffsetNumber offnum,
maxoff;
maxoff = PageGetMaxOffsetNumber(page);
for (offnum = FirstOffsetNumber;
offnum <= maxoff;
offnum = OffsetNumberNext(offnum))
{
ItemId itemId = PageGetItemId(page, offnum);
if (ItemIdIsUsed(itemId))
itemId->lp_flags = LP_UNUSED;
}
}
/*
* mask_page_content
*
* In some index AMs, the contents of deleted pages need to be almost
* completely ignored.
*/
void
mask_page_content(Page page)
{
/* Mask Page Content */
memset(page + SizeOfPageHeaderData, MASK_MARKER,
BLCKSZ - SizeOfPageHeaderData);
/* Mask pd_lower and pd_upper */
memset(&((PageHeader) page)->pd_lower, MASK_MARKER,
sizeof(uint16));
memset(&((PageHeader) page)->pd_upper, MASK_MARKER,
sizeof(uint16));
}
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