Allow pgoutput to send logical decoding messages.

The output plugin accepts a new parameter (messages) that controls if
logical decoding messages are written into the replication stream. It is
useful for those clients that use pgoutput as an output plugin and needs
to process messages that were written by pg_logical_emit_message().

Although logical streaming replication protocol supports logical
decoding messages now, logical replication does not use this feature yet.

Author: David Pirotte, Euler Taveira
Reviewed-by: Euler Taveira, Andres Freund, Ashutosh Bapat, Amit Kapila
Discussion: https://postgr.es/m/CADK3HHJ-+9SO7KuRLH=9Wa1rAo60Yreq1GFNkH_kd0=CdaWM+A@mail.gmail.com

1 files changed, 47 insertions, 0 deletions

diff --git a/src/backend/replication/pgoutput/pgoutput.c b/src/backend/replication/pgoutput/pgoutput.c
index 6146c5acdb3..f68348dcf45 100644
--- a/src/backend/replication/pgoutput/pgoutput.c
+++ b/src/backend/replication/pgoutput/pgoutput.c
@@ -45,6 +45,10 @@ static void pgoutput_change(LogicalDecodingContext *ctx,
 static void pgoutput_truncate(LogicalDecodingContext *ctx,
 							  ReorderBufferTXN *txn, int nrelations, Relation relations[],
 							  ReorderBufferChange *change);
+static void pgoutput_message(LogicalDecodingContext *ctx,
+							 ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							 bool transactional, const char *prefix,
+							 Size sz, const char *message);
 static bool pgoutput_origin_filter(LogicalDecodingContext *ctx,
 								   RepOriginId origin_id);
 static void pgoutput_stream_start(struct LogicalDecodingContext *ctx,
@@ -142,6 +146,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->begin_cb = pgoutput_begin_txn;
 	cb->change_cb = pgoutput_change;
 	cb->truncate_cb = pgoutput_truncate;
+	cb->message_cb = pgoutput_message;
 	cb->commit_cb = pgoutput_commit_txn;
 	cb->filter_by_origin_cb = pgoutput_origin_filter;
 	cb->shutdown_cb = pgoutput_shutdown;
@@ -152,6 +157,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->stream_abort_cb = pgoutput_stream_abort;
 	cb->stream_commit_cb = pgoutput_stream_commit;
 	cb->stream_change_cb = pgoutput_change;
+	cb->stream_message_cb = pgoutput_message;
 	cb->stream_truncate_cb = pgoutput_truncate;
 }
 
@@ -162,10 +168,12 @@ parse_output_parameters(List *options, PGOutputData *data)
 	bool		protocol_version_given = false;
 	bool		publication_names_given = false;
 	bool		binary_option_given = false;
+	bool		messages_option_given = false;
 	bool		streaming_given = false;
 
 	data->binary = false;
 	data->streaming = false;
+	data->messages = false;
 
 	foreach(lc, options)
 	{
@@ -221,6 +229,16 @@ parse_output_parameters(List *options, PGOutputData *data)
 
 			data->binary = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "messages") == 0)
+		{
+			if (messages_option_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			messages_option_given = true;
+
+			data->messages = defGetBoolean(defel);
+		}
 		else if (strcmp(defel->defname, "streaming") == 0)
 		{
 			if (streaming_given)
@@ -689,6 +707,35 @@ pgoutput_truncate(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 	MemoryContextReset(data->context);
 }
 
+static void
+pgoutput_message(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
+				 XLogRecPtr message_lsn, bool transactional, const char *prefix, Size sz,
+				 const char *message)
+{
+	PGOutputData *data = (PGOutputData *) ctx->output_plugin_private;
+	TransactionId xid = InvalidTransactionId;
+
+	if (!data->messages)
+		return;
+
+	/*
+	 * Remember the xid for the message in streaming mode. See
+	 * pgoutput_change.
+	 */
+	if (in_streaming)
+		xid = txn->xid;
+
+	OutputPluginPrepareWrite(ctx, true);
+	logicalrep_write_message(ctx->out,
+							 xid,
+							 message_lsn,
+							 transactional,
+							 prefix,
+							 sz,
+							 message);
+	OutputPluginWrite(ctx, true);
+}
+
 /*
  * Currently we always forward.
  */