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       1                 :             : /*-------------------------------------------------------------------------
       2                 :             :  *
       3                 :             :  * message.c
       4                 :             :  *        Generic logical messages.
       5                 :             :  *
       6                 :             :  * Copyright (c) 2013-2026, PostgreSQL Global Development Group
       7                 :             :  *
       8                 :             :  * IDENTIFICATION
       9                 :             :  *        src/backend/replication/logical/message.c
      10                 :             :  *
      11                 :             :  * NOTES
      12                 :             :  *
      13                 :             :  * Generic logical messages allow XLOG logging of arbitrary binary blobs that
      14                 :             :  * get passed to the logical decoding plugin. In normal XLOG processing they
      15                 :             :  * are same as NOOP.
      16                 :             :  *
      17                 :             :  * These messages can be either transactional or non-transactional.
      18                 :             :  * Transactional messages are part of current transaction and will be sent to
      19                 :             :  * decoding plugin using in a same way as DML operations.
      20                 :             :  * Non-transactional messages are sent to the plugin at the time when the
      21                 :             :  * logical decoding reads them from XLOG. This also means that transactional
      22                 :             :  * messages won't be delivered if the transaction was rolled back but the
      23                 :             :  * non-transactional one will always be delivered.
      24                 :             :  *
      25                 :             :  * Every message carries prefix to avoid conflicts between different decoding
      26                 :             :  * plugins. The plugin authors must take extra care to use unique prefix,
      27                 :             :  * good options seems to be for example to use the name of the extension.
      28                 :             :  *
      29                 :             :  * ---------------------------------------------------------------------------
      30                 :             :  */
      31                 :             : 
      32                 :             : #include "postgres.h"
      33                 :             : 
      34                 :             : #include "access/xact.h"
      35                 :             : #include "access/xloginsert.h"
      36                 :             : #include "miscadmin.h"
      37                 :             : #include "replication/message.h"
      38                 :             : 
      39                 :             : /*
      40                 :             :  * Write logical decoding message into XLog.
      41                 :             :  */
      42                 :             : XLogRecPtr
      43                 :           0 : LogLogicalMessage(const char *prefix, const char *message, size_t size,
      44                 :             :                                   bool transactional, bool flush)
      45                 :             : {
      46                 :           0 :         xl_logical_message xlrec;
      47                 :           0 :         XLogRecPtr      lsn;
      48                 :             : 
      49                 :             :         /*
      50                 :             :          * Force xid to be allocated if we're emitting a transactional message.
      51                 :             :          */
      52         [ #  # ]:           0 :         if (transactional)
      53                 :             :         {
      54         [ #  # ]:           0 :                 Assert(IsTransactionState());
      55                 :           0 :                 GetCurrentTransactionId();
      56                 :           0 :         }
      57                 :             : 
      58                 :           0 :         xlrec.dbId = MyDatabaseId;
      59                 :           0 :         xlrec.transactional = transactional;
      60                 :             :         /* trailing zero is critical; see logicalmsg_desc */
      61                 :           0 :         xlrec.prefix_size = strlen(prefix) + 1;
      62                 :           0 :         xlrec.message_size = size;
      63                 :             : 
      64                 :           0 :         XLogBeginInsert();
      65                 :           0 :         XLogRegisterData(&xlrec, SizeOfLogicalMessage);
      66                 :           0 :         XLogRegisterData(prefix, xlrec.prefix_size);
      67                 :           0 :         XLogRegisterData(message, size);
      68                 :             : 
      69                 :             :         /* allow origin filtering */
      70                 :           0 :         XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
      71                 :             : 
      72                 :           0 :         lsn = XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
      73                 :             : 
      74                 :             :         /*
      75                 :             :          * Make sure that the message hits disk before leaving if emitting a
      76                 :             :          * non-transactional message when flush is requested.
      77                 :             :          */
      78   [ #  #  #  # ]:           0 :         if (!transactional && flush)
      79                 :           0 :                 XLogFlush(lsn);
      80                 :           0 :         return lsn;
      81                 :           0 : }
      82                 :             : 
      83                 :             : /*
      84                 :             :  * Redo is basically just noop for logical decoding messages.
      85                 :             :  */
      86                 :             : void
      87                 :           0 : logicalmsg_redo(XLogReaderState *record)
      88                 :             : {
      89                 :           0 :         uint8           info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
      90                 :             : 
      91         [ #  # ]:           0 :         if (info != XLOG_LOGICAL_MESSAGE)
      92   [ #  #  #  # ]:           0 :                 elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
      93                 :             : 
      94                 :             :         /* This is only interesting for logical decoding, see decode.c. */
      95                 :           0 : }