Generic Messages for Logical Decoding

API and mechanism to allow generic messages to be inserted into WAL that are
intended to be read by logical decoding plugins. This commit adds an optional
new callback to the logical decoding API.

Messages are either text or bytea. Messages can be transactional, or not, and
are identified by a prefix to allow multiple concurrent decoding plugins.

(Not to be confused with Generic WAL records, which are intended to allow crash
recovery of extensible objects.)

Author: Petr Jelinek and Andres Freund
Reviewers: Artur Zakirov, Tomas Vondra, Simon Riggs
Discussion: [email protected]

1 files changed, 18 insertions, 0 deletions

diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f2814..3336e1e16e7 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,10 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +87,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +477,15 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn, bool transactional,
+				  const char *prefix, Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 transactional, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}