From: PG Bug reporting form <noreply@postgresql.org>
To: pgsql-bugs@lists.postgresql.org
Cc: xu.xw2008@163.com
Subject: BUG #17903: There is a bug in the KeepLogSeg()
Date: Wed, 19 Apr 2023 10:26:13 +0000
Message-ID: <17903-4288d439dee856c6@postgresql.org> (raw)
The following bug has been logged on the website:
Bug reference: 17903
Logged by: xu xingwang
Email address: xu.xw2008@163.com
PostgreSQL version: 13.3
Operating system: openEuler
Description:
Hi,
I found that KeepLogSeg() has a piece of code that is not correctly.
segno may be larger than currSegNo, since the slot_keep_segs variable is of
type "uint64", in this case the code "if (currSegNo - segno >
slot_keep_segs)" is incorrect.
"if (currSegNo - segno < keep_segs)" is also the same.
Checkpoint calls the KeepLogSeg function, and there are many operations
between recptr and XLogGetReplicationSlotMinimumLSN, including updating the
pg_control file, so segno may be larger than currSegNo.
KeepLogSeg(XLogRecPtr recptr, XLogSegNo *logSegNo)
{
XLogSegNo currSegNo;
XLogSegNo segno;
XLogRecPtr keep;
XLByteToSeg(recptr, currSegNo, wal_segment_size);
segno = currSegNo;
/*
* Calculate how many segments are kept by slots first, adjusting for
* max_slot_wal_keep_size.
*/
keep = XLogGetReplicationSlotMinimumLSN();
if (keep != InvalidXLogRecPtr)
{
XLByteToSeg(keep, segno, wal_segment_size);
/* Cap by max_slot_wal_keep_size ... */
if (max_slot_wal_keep_size_mb >= 0)
{
uint64 slot_keep_segs;
slot_keep_segs =
ConvertToXSegs(max_slot_wal_keep_size_mb, wal_segment_size);
if (currSegNo - segno > slot_keep_segs)
segno = currSegNo - slot_keep_segs;
}
}
/* but, keep at least wal_keep_size if that's set */
if (wal_keep_size_mb > 0)
{
uint64 keep_segs;
keep_segs = ConvertToXSegs(wal_keep_size_mb, wal_segment_size);
if (currSegNo - segno < keep_segs)
{
/* avoid underflow, don't go below 1 */
if (currSegNo <= keep_segs)
segno = 1;
else
segno = currSegNo - keep_segs;
}
}
regards.
--
xu xingwang
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Cc: noreply@postgresql.org, pgsql-bugs@lists.postgresql.org, xu.xw2008@163.com
Subject: Re: BUG #17903: There is a bug in the KeepLogSeg()
In-Reply-To: <17903-4288d439dee856c6@postgresql.org>
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