Hi,
Right now pg_waldump just prints whether the message is transactional
or not and its size. That doesn't help much to understand the message
itself. If it prints the contents of a logical WAL message, it helps
debugging logical replication related problems. Prefix is a
null-terminated ASCII string, so no problem printing that. Even the
contents can be printed as a series of hex bytes. Here's a patch to do
that.
I tested this manually as below
postgres=# select pg_logical_emit_message(false, 'some_prefix', 'some
message'::text);
pg_logical_emit_message
-------------------------
0/1570658
(1 row)
$> pg_waldump --start 0/1570600 -p data/
first record is after 0/1570600, at 0/1570608, skipping over 8 bytes
rmgr: LogicalMessage len (rec/tot): 74/ 74, tx: 0,
lsn: 0/01570608, prev 0/015705D0, desc: MESSAGE nontransactional
message size 12 bytes, prefix some_prefix; mesage: 73 6F 6D 65 20 6D
65 73 73 61 67 65
rmgr: Standby len (rec/tot): 50/ 50, tx: 0, lsn:
0/01570658, prev 0/01570608, desc: RUNNING_XACTS nextXid 504
latestCompletedXid 503 oldestRunningXid 504
pg_waldump: fatal: error in WAL record at 0/1570658: invalid record
length at 0/1570690: wanted 24, got 0
I didn't find any tests for pg_waldump to test its output, so haven't
added one in the patch.
--
Best Wishes,
Ashutosh Bapat
From 1547277944f7aceb1d5b0a3ae46ec2acf02f3b06 Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.ba...@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
---
src/backend/access/rmgrdesc/logicalmsgdesc.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
index bff298c928..fdd03362e7 100644
--- a/src/backend/access/rmgrdesc/logicalmsgdesc.c
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -24,10 +24,24 @@ logicalmsg_desc(StringInfo buf, XLogReaderState *record)
if (info == XLOG_LOGICAL_MESSAGE)
{
xl_logical_message *xlrec = (xl_logical_message *) rec;
+ /*
+ * Per LogLogicalMessage() actual logical message follows a null-terminated prefix of length
+ * prefix_size.
+ */
+ char *prefix = xlrec->message;
+ char *message = xlrec->message + xlrec->prefix_size;
+ int cnt;
+ char *sep = "";
- appendStringInfo(buf, "%s message size %zu bytes",
+ appendStringInfo(buf, "%s message size %zu bytes, prefix %s; mesage: ",
xlrec->transactional ? "transactional" : "nontransactional",
- xlrec->message_size);
+ xlrec->message_size, prefix);
+ /* 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 = " ";
+ }
}
}
--
2.17.1
