Line data    Source code

       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         2337 : seq_redo(XLogReaderState *record)
      24              : {
      25         2337 :     XLogRecPtr  lsn = record->EndRecPtr;
      26         2337 :     uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
      27              :     Buffer      buffer;
      28              :     Page        page;
      29              :     Page        localpage;
      30              :     char       *item;
      31              :     Size        itemsz;
      32         2337 :     xl_seq_rec *xlrec = (xl_seq_rec *) XLogRecGetData(record);
      33              :     sequence_magic *sm;
      34              : 
      35         2337 :     if (info != XLOG_SEQ_LOG)
      36            0 :         elog(PANIC, "seq_redo: unknown op code %u", info);
      37              : 
      38         2337 :     buffer = XLogInitBufferForRedo(record, 0);
      39         2337 :     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         2337 :     localpage = (Page) palloc(BufferGetPageSize(buffer));
      51              : 
      52         2337 :     PageInit(localpage, BufferGetPageSize(buffer), sizeof(sequence_magic));
      53         2337 :     sm = (sequence_magic *) PageGetSpecialPointer(localpage);
      54         2337 :     sm->magic = SEQ_MAGIC;
      55              : 
      56         2337 :     item = (char *) xlrec + sizeof(xl_seq_rec);
      57         2337 :     itemsz = XLogRecGetDataLen(record) - sizeof(xl_seq_rec);
      58              : 
      59         2337 :     if (PageAddItem(localpage, item, itemsz, FirstOffsetNumber, false, false) == InvalidOffsetNumber)
      60            0 :         elog(PANIC, "seq_redo: failed to add item to page");
      61              : 
      62         2337 :     PageSetLSN(localpage, lsn);
      63              : 
      64         2337 :     memcpy(page, localpage, BufferGetPageSize(buffer));
      65         2337 :     MarkBufferDirty(buffer);
      66         2337 :     UnlockReleaseBuffer(buffer);
      67              : 
      68         2337 :     pfree(localpage);
      69         2337 : }
      70              : 
      71              : /*
      72              :  * Mask a Sequence page before performing consistency checks on it.
      73              :  */
      74              : void
      75         1208 : seq_mask(char *page, BlockNumber blkno)
      76              : {
      77         1208 :     mask_page_lsn_and_checksum(page);
      78              : 
      79         1208 :     mask_unused_space(page);
      80         1208 : }