TLA  Line data    Source code

       1                 : /*-------------------------------------------------------------------------
       2                 :  *
       3                 :  * message.c
       4                 :  *    Generic logical messages.
       5                 :  *
       6                 :  * Copyright (c) 2013-2023, 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 "nodes/execnodes.h"
      38                 : #include "replication/logical.h"
      39                 : #include "replication/message.h"
      40                 : #include "utils/memutils.h"
      41                 : 
      42                 : /*
      43                 :  * Write logical decoding message into XLog.
      44                 :  */
      45                 : XLogRecPtr
      46 CBC          22 : LogLogicalMessage(const char *prefix, const char *message, size_t size,
      47                 :                   bool transactional)
      48                 : {
      49                 :     xl_logical_message xlrec;
      50                 : 
      51                 :     /*
      52                 :      * Force xid to be allocated if we're emitting a transactional message.
      53                 :      */
      54              22 :     if (transactional)
      55                 :     {
      56              14 :         Assert(IsTransactionState());
      57              14 :         GetCurrentTransactionId();
      58                 :     }
      59                 : 
      60              22 :     xlrec.dbId = MyDatabaseId;
      61              22 :     xlrec.transactional = transactional;
      62                 :     /* trailing zero is critical; see logicalmsg_desc */
      63              22 :     xlrec.prefix_size = strlen(prefix) + 1;
      64              22 :     xlrec.message_size = size;
      65                 : 
      66              22 :     XLogBeginInsert();
      67              22 :     XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
      68              22 :     XLogRegisterData(unconstify(char *, prefix), xlrec.prefix_size);
      69              22 :     XLogRegisterData(unconstify(char *, message), size);
      70                 : 
      71                 :     /* allow origin filtering */
      72              22 :     XLogSetRecordFlags(XLOG_INCLUDE_ORIGIN);
      73                 : 
      74              22 :     return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
      75                 : }
      76                 : 
      77                 : /*
      78                 :  * Redo is basically just noop for logical decoding messages.
      79                 :  */
      80                 : void
      81               1 : logicalmsg_redo(XLogReaderState *record)
      82                 : {
      83               1 :     uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
      84                 : 
      85               1 :     if (info != XLOG_LOGICAL_MESSAGE)
      86 UBC           0 :         elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
      87                 : 
      88                 :     /* This is only interesting for logical decoding, see decode.c. */
      89 CBC           1 : }