| From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
|---|---|
| To: | "Zhijie Hou (Fujitsu)" <houzj(dot)fnst(at)fujitsu(dot)com> |
| Cc: | shveta malik <shveta(dot)malik(at)gmail(dot)com>, Peter Smith <smithpb2250(at)gmail(dot)com>, Ajin Cherian <itsajin(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Nisha Moond <nisha(dot)moond412(at)gmail(dot)com>, "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Subject: | Re: Synchronizing slots from primary to standby |
| Date: | 2024-02-09 04:34:42 |
| Message-ID: | CAA4eK1LcM2Xv0KZRWDAu3b-_8AU2C6=LA4c0p7ageHiE0MQvng@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Feb 9, 2024 at 10:00 AM Zhijie Hou (Fujitsu)
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> Here is the V82 patch set which includes the following changes:
>
+reserve_wal_for_local_slot(XLogRecPtr restart_lsn)
{
...
+ /*
+ * Find the oldest existing WAL segment file.
+ *
+ * Normally, we can determine it by using the last removed segment
+ * number. However, if no WAL segment files have been removed by a
+ * checkpoint since startup, we need to search for the oldest segment
+ * file currently existing in XLOGDIR.
+ */
+ oldest_segno = XLogGetLastRemovedSegno() + 1;
+
+ if (oldest_segno == 1)
+ {
+ TimeLineID cur_timeline;
+
+ GetWalRcvFlushRecPtr(NULL, &cur_timeline);
+ oldest_segno = XLogGetOldestSegno(cur_timeline);
...
...
This means that if the restart_lsn of the slot is from the prior
timeline then the standby needs to wait for longer times to sync the
slot. Ideally, it should be okay because I don't think even if
restart_lsn of the slot may be from some prior timeline than the
current flush timeline on standby, how often that case can happen?
OTOH, in the prior version patch(v80_2-0001*), we search for the
oldest segment in all possible timelines via code like:
+reserve_wal_for_local_slot(XLogRecPtr restart_lsn)
{
...
+ */
+ oldest_segno = XLogGetLastRemovedSegno() + 1;
+
+ if (oldest_segno == 1)
+ oldest_segno = XLogGetOldestSegno(0);
I don't see a problem either way as in both scenarios this is a very
rare case and doesn't seem to cause any problem but would like to know
the opinion of others.
--
With Regards,
Amit Kapila.
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