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help / color / mirror / Atom feedFrom: shveta malik <[email protected]>
To: Zhijie Hou (Fujitsu) <[email protected]>
Cc: Amit Kapila <[email protected]>
Cc: Ajin Cherian <[email protected]>
Cc: Hayato Kuroda (Fujitsu) <[email protected]>
Cc: Ashutosh Sharma <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: shveta malik <[email protected]>
Subject: Re: [PATCH] Support automatic sequence replication
Date: Thu, 5 Mar 2026 11:18:20 +0530
Message-ID: <CAJpy0uBeAdz6-3P26Eryeq3TyjA-GiKY3z0hFMxzZD=AYGqQ3Q@mail.gmail.com> (raw)
In-Reply-To: <CAJpy0uAfu-VPqCknLLvJ+PUx_cyoR-b70xUNT6Pyv8N-odKizQ@mail.gmail.com>
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On Thu, Mar 5, 2026 at 9:35 AM shveta malik <[email protected]> wrote:
>
> On Thu, Mar 5, 2026 at 8:16 AM Zhijie Hou (Fujitsu)
> <[email protected]> wrote:
> >
> >
> > Here is V10 patch set which addressed all comments.
> >
>
> Thank You. Please find a few comments on 001:
>
A concern in 002:
I realized that below might not be the correct logic to avoid
overwriting sequences at sub which are already at latest values.
+ /*
+ * Skip synchronization if the local sequence value is already ahead of
+ * the publisher's value.
...
+ */
+ if (local_last_value > seqinfo->last_value)
+ {
+ ereport(WARNING,
+ errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("skipped synchronizing the sequence \"%s.%s\"",
+ seqinfo->nspname, seqinfo->seqname),
+ errdetail("The local last_value %lld is ahead of the one on publisher",
+ (long long int) local_last_value));
+
+ return COPYSEQ_NO_DRIFT;
+ }
A sequence could be descending one too and thus we may wrongly end up
avoiding synchronization. We should first check if it is descending or
ascending (perhaps by checking if increment_by < 0 or >0), then decide
to manage conflict.
Example:
postgres=# CREATE SEQUENCE desc_seq START WITH 1000 INCREMENT BY -1
MINVALUE 1 MAXVALUE 1000;
CREATE SEQUENCE
postgres=# select nextval('desc_seq');
nextval
---------
1000
postgres=# select nextval('desc_seq');
nextval
---------
999
Doc also mentions descending sequences. See [1] (search for descending).
[1]: https://www.postgresql.org/docs/18/sql-createsequence.html
thanks
Shveta
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Subject: Re: [PATCH] Support automatic sequence replication
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