/*-------------------------------------------------------------------------

 *

 * sequence.c

 *    RMGR WAL routines for sequences.

 *

 * Portions Copyright (c) 1996-2026, 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);

  XLogFlushBufferForRedoIfInit(record, 0, 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);

}