Hi, hackers!
I propose the patch for fix one small code defect.
The XLogReadRecord() function reads the pages of a WAL segment that
contain a WAL-record. Then it creates a readRecordBuf buffer in private
memory of a backend and copy record from the pages to the readRecordBuf
buffer. Pointer 'record' is set to the beginning of the readRecordBuf
buffer.
But if the WAL-record is fully placed on one page, the XLogReadRecord()
function forgets to bind the "record" pointer with the beginning of the
readRecordBuf buffer. In this case, XLogReadRecord() returns a pointer
to an internal xlog page. This patch fixes the defect.
Previously, in all cases of using WAL this was not a problem. However if
you plan to perform some decoding operations before returning the WAL
record to the caller (this is my case), this can lead to bugs that are
difficult to catch.
--
Andrey Lepikhov
Postgres Professional
https://postgrespro.com
The Russian Postgres Company
>From 0a7d7bf07eb91a959b2864a7497088c4d203aaa4 Mon Sep 17 00:00:00 2001
From: "Andrey V. Lepikhov" <a.lepik...@postgrespro.ru>
Date: Fri, 17 Aug 2018 07:56:30 +0500
Subject: [PATCH] WAL record local buffer pointer fix
---
src/backend/access/transam/xlogreader.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 4c633c6c49..7bccc68189 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -480,6 +480,7 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
state->ReadRecPtr = RecPtr;
memcpy(state->readRecordBuf, record, total_len);
+ record = (XLogRecord *) state->readRecordBuf;
}
/*
--
2.17.1
