sequence_xlog.c

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/*-------------------------------------------------------------------------
 *
 * sequence.c
 *    RMGR WAL routines for sequences.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/sequence_xlog.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/bufmask.h"
#include "access/xlogutils.h"
#include "commands/sequence_xlog.h"
#include "storage/bufmgr.h"
 
void
seq_redo(XLogReaderState *record)
{
    XLogRecPtr  lsn = record->EndRecPtr;
    uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
    Buffer      buffer;
    Page        page;
    Page        localpage;
    char       *item;
    Size        itemsz;
    xl_seq_rec *xlrec = (xl_seq_rec *) XLogRecGetData(record);
    sequence_magic *sm;
 
    if (info != XLOG_SEQ_LOG)
        elog(PANIC, "seq_redo: unknown op code %u", info);
 
    buffer = XLogInitBufferForRedo(record, 0);
    page = BufferGetPage(buffer);
 
    /*
     * We always reinit the page.  However, since this WAL record type is also
     * used for updating sequences, it's possible that a hot-standby backend
     * is examining the page concurrently; so we mustn't transiently trash the
     * buffer.  The solution is to build the correct new page contents in
     * local workspace and then memcpy into the buffer.  Then only bytes that
     * are supposed to change will change, even transiently. We must palloc
     * the local page for alignment reasons.
     */
    localpage = (Page) palloc(BufferGetPageSize(buffer));
 
    PageInit(localpage, BufferGetPageSize(buffer), sizeof(sequence_magic));
    sm = (sequence_magic *) PageGetSpecialPointer(localpage);
    sm->magic = SEQ_MAGIC;
 
    item = (char *) xlrec + sizeof(xl_seq_rec);
    itemsz = XLogRecGetDataLen(record) - sizeof(xl_seq_rec);
 
    if (PageAddItem(localpage, item, itemsz, FirstOffsetNumber, false, false) == InvalidOffsetNumber)
        elog(PANIC, "seq_redo: failed to add item to page");
 
    PageSetLSN(localpage, lsn);
 
    memcpy(page, localpage, BufferGetPageSize(buffer));
    MarkBufferDirty(buffer);
    UnlockReleaseBuffer(buffer);
 
    pfree(localpage);
}
 
/*
 * Mask a Sequence page before performing consistency checks on it.
 */
void
seq_mask(char *page, BlockNumber blkno)
{
    mask_page_lsn_and_checksum(page);
 
    mask_unused_space(page);
}