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       1                 :             : /*-------------------------------------------------------------------------
       2                 :             :  *
       3                 :             :  * sequence.c
       4                 :             :  *        RMGR WAL routines for sequences.
       5                 :             :  *
       6                 :             :  * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
       7                 :             :  * Portions Copyright (c) 1994, Regents of the University of California
       8                 :             :  *
       9                 :             :  *
      10                 :             :  * IDENTIFICATION
      11                 :             :  *        src/backend/commands/sequence_xlog.c
      12                 :             :  *
      13                 :             :  *-------------------------------------------------------------------------
      14                 :             :  */
      15                 :             : #include "postgres.h"
      16                 :             : 
      17                 :             : #include "access/bufmask.h"
      18                 :             : #include "access/xlogutils.h"
      19                 :             : #include "commands/sequence_xlog.h"
      20                 :             : #include "storage/bufmgr.h"
      21                 :             : 
      22                 :             : void
      23                 :           0 : seq_redo(XLogReaderState *record)
      24                 :             : {
      25                 :           0 :         XLogRecPtr      lsn = record->EndRecPtr;
      26                 :           0 :         uint8           info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
      27                 :           0 :         Buffer          buffer;
      28                 :           0 :         Page            page;
      29                 :           0 :         Page            localpage;
      30                 :           0 :         char       *item;
      31                 :           0 :         Size            itemsz;
      32                 :           0 :         xl_seq_rec *xlrec = (xl_seq_rec *) XLogRecGetData(record);
      33                 :           0 :         sequence_magic *sm;
      34                 :             : 
      35         [ #  # ]:           0 :         if (info != XLOG_SEQ_LOG)
      36   [ #  #  #  # ]:           0 :                 elog(PANIC, "seq_redo: unknown op code %u", info);
      37                 :             : 
      38                 :           0 :         buffer = XLogInitBufferForRedo(record, 0);
      39                 :           0 :         page = BufferGetPage(buffer);
      40                 :             : 
      41                 :             :         /*
      42                 :             :          * We always reinit the page.  However, since this WAL record type is also
      43                 :             :          * used for updating sequences, it's possible that a hot-standby backend
      44                 :             :          * is examining the page concurrently; so we mustn't transiently trash the
      45                 :             :          * buffer.  The solution is to build the correct new page contents in
      46                 :             :          * local workspace and then memcpy into the buffer.  Then only bytes that
      47                 :             :          * are supposed to change will change, even transiently. We must palloc
      48                 :             :          * the local page for alignment reasons.
      49                 :             :          */
      50                 :           0 :         localpage = (Page) palloc(BufferGetPageSize(buffer));
      51                 :             : 
      52                 :           0 :         PageInit(localpage, BufferGetPageSize(buffer), sizeof(sequence_magic));
      53                 :           0 :         sm = (sequence_magic *) PageGetSpecialPointer(localpage);
      54                 :           0 :         sm->magic = SEQ_MAGIC;
      55                 :             : 
      56                 :           0 :         item = (char *) xlrec + sizeof(xl_seq_rec);
      57                 :           0 :         itemsz = XLogRecGetDataLen(record) - sizeof(xl_seq_rec);
      58                 :             : 
      59         [ #  # ]:           0 :         if (PageAddItem(localpage, item, itemsz, FirstOffsetNumber, false, false) == InvalidOffsetNumber)
      60   [ #  #  #  # ]:           0 :                 elog(PANIC, "seq_redo: failed to add item to page");
      61                 :             : 
      62                 :           0 :         PageSetLSN(localpage, lsn);
      63                 :             : 
      64                 :           0 :         memcpy(page, localpage, BufferGetPageSize(buffer));
      65                 :           0 :         MarkBufferDirty(buffer);
      66                 :           0 :         UnlockReleaseBuffer(buffer);
      67                 :             : 
      68                 :           0 :         pfree(localpage);
      69                 :           0 : }
      70                 :             : 
      71                 :             : /*
      72                 :             :  * Mask a Sequence page before performing consistency checks on it.
      73                 :             :  */
      74                 :             : void
      75                 :           0 : seq_mask(char *page, BlockNumber blkno)
      76                 :             : {
      77                 :           0 :         mask_page_lsn_and_checksum(page);
      78                 :             : 
      79                 :           0 :         mask_unused_space(page);
      80                 :           0 : }