0001-Print-prefix-and-logical-WAL-message-content-in-pg_w.v2.patch

From d32859c8368ac25366b156c3247a5b77d9b72ce8 Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat@2ndquadrant.com>
Date: Tue, 18 Aug 2020 11:05:29 +0530
Subject: [PATCH] Print prefix and logical WAL message content in pg_waldump

Print logical WAL message prefix which is a null terminated ASCII
string. Print the actual message as a space separated hex byte string
since it may contain binary data. This is useful for debugging purposes.

Ashutosh Bapat, reviewed by Alvaro Herrera
---
 src/backend/access/rmgrdesc/logicalmsgdesc.c | 16 ++++++++++++++--
 src/include/replication/message.h            |  4 +++-
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
index bff298c928..5da2625a0b 100644
--- a/src/backend/access/rmgrdesc/logicalmsgdesc.c
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -24,10 +24,22 @@ logicalmsg_desc(StringInfo buf, XLogReaderState *record)
 	if (info == XLOG_LOGICAL_MESSAGE)
 	{
 		xl_logical_message *xlrec = (xl_logical_message *) rec;
+		char   *prefix = xlrec->message;
+		char   *message = xlrec->message + xlrec->prefix_size;
+		int		cnt;
+		char   *sep = "";
 
-		appendStringInfo(buf, "%s message size %zu bytes",
+		Assert(prefix[xlrec->prefix_size] != '\0');
+
+		appendStringInfo(buf, "%s, prefix \"%s\"; payload (%zu bytes): ",
 						 xlrec->transactional ? "transactional" : "nontransactional",
-						 xlrec->message_size);
+						 prefix, xlrec->message_size);
+		/* Write actual message as a series of hex bytes. */
+		for (cnt = 0; cnt < xlrec->message_size; cnt++)
+		{
+			appendStringInfo(buf, "%s%02X", sep, (unsigned char)message[cnt]);
+			sep = " ";
+		}
 	}
 }
 
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
index 937addde48..7b882296ec 100644
--- a/src/include/replication/message.h
+++ b/src/include/replication/message.h
@@ -25,7 +25,9 @@ typedef struct xl_logical_message
 	Size		message_size;	/* size of the message */
 	char		message[FLEXIBLE_ARRAY_MEMBER]; /* message including the null
 												 * terminated prefix of length
-												 * prefix_size */
+												 * prefix_size. Please see
+												 * logicalmsg_desc(), if you
+												 * change this. */
 } xl_logical_message;
 
 #define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
-- 
2.17.1