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: 5685F999.6010202@2ndquadrant.com

3 files changed, 45 insertions, 3 deletions

diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c0e38fdf17d..5514db1dda6 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o genericdesc.o \
-	   gindesc.o gistdesc.o hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o \
-	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
-	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
+	   gindesc.o gistdesc.o hashdesc.o heapdesc.o logicalmsgdesc.o \
+	   mxactdesc.o nbtdesc.o relmapdesc.o replorigindesc.o seqdesc.o \
+	   smgrdesc.o spgdesc.o standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 00000000000..b194e1424d8
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7b38c16f521..31c5fd165c0 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -24,6 +24,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"