Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * sequence.c
       4             :  *    RMGR WAL routines for sequences.
       5             :  *
       6             :  * Portions Copyright (c) 1996-2025, 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        4650 : seq_redo(XLogReaderState *record)
      24             : {
      25        4650 :     XLogRecPtr  lsn = record->EndRecPtr;
      26        4650 :     uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
      27             :     Buffer      buffer;
      28             :     Page        page;
      29             :     Page        localpage;
      30             :     char       *item;
      31             :     Size        itemsz;
      32        4650 :     xl_seq_rec *xlrec = (xl_seq_rec *) XLogRecGetData(record);
      33             :     sequence_magic *sm;
      34             : 
      35        4650 :     if (info != XLOG_SEQ_LOG)
      36           0 :         elog(PANIC, "seq_redo: unknown op code %u", info);
      37             : 
      38        4650 :     buffer = XLogInitBufferForRedo(record, 0);
      39        4650 :     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        4650 :     localpage = (Page) palloc(BufferGetPageSize(buffer));
      51             : 
      52        4650 :     PageInit(localpage, BufferGetPageSize(buffer), sizeof(sequence_magic));
      53        4650 :     sm = (sequence_magic *) PageGetSpecialPointer(localpage);
      54        4650 :     sm->magic = SEQ_MAGIC;
      55             : 
      56        4650 :     item = (char *) xlrec + sizeof(xl_seq_rec);
      57        4650 :     itemsz = XLogRecGetDataLen(record) - sizeof(xl_seq_rec);
      58             : 
      59        4650 :     if (PageAddItem(localpage, item, itemsz, FirstOffsetNumber, false, false) == InvalidOffsetNumber)
      60           0 :         elog(PANIC, "seq_redo: failed to add item to page");
      61             : 
      62        4650 :     PageSetLSN(localpage, lsn);
      63             : 
      64        4650 :     memcpy(page, localpage, BufferGetPageSize(buffer));
      65        4650 :     MarkBufferDirty(buffer);
      66        4650 :     UnlockReleaseBuffer(buffer);
      67             : 
      68        4650 :     pfree(localpage);
      69        4650 : }
      70             : 
      71             : /*
      72             :  * Mask a Sequence page before performing consistency checks on it.
      73             :  */
      74             : void
      75        2372 : seq_mask(char *page, BlockNumber blkno)
      76             : {
      77        2372 :     mask_page_lsn_and_checksum(page);
      78             : 
      79        2372 :     mask_unused_space(page);
      80        2372 : }