| From: | Michael Paquier <michael(at)paquier(dot)xyz> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | vignesh C <vignesh21(at)gmail(dot)com>, shveta malik <shveta(dot)malik(at)gmail(dot)com>, Shlok Kyal <shlok(dot)kyal(dot)oss(at)gmail(dot)com>, Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com>, Nisha Moond <nisha(dot)moond412(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Peter Smith <smithpb2250(at)gmail(dot)com>, Peter Eisentraut <peter(at)eisentraut(dot)org>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Euler Taveira <euler(at)eulerto(dot)com>, "Zhijie Hou (Fujitsu)" <houzj(dot)fnst(at)fujitsu(dot)com>, "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org> |
| Subject: | Re: Logical Replication of sequences |
| Date: | 2025-10-05 02:23:54 |
| Message-ID: | aOHWusf1WkHapo-C@paquier.xyz |
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| Lists: | pgsql-hackers |
On Sat, Oct 04, 2025 at 09:24:32PM +0530, Amit Kapila wrote:
> In the 0001 patch, pg_get_sequence_data() exposes two new fields
> log_cnt and page_lsn. I see that the later subscriber-side patch uses
> both, the first one in SetSequence(). It is not clear from the
> comments or the commit message of 0001 why it is necessary to use
> log_cnt when setting the sequence. Can you explain what the problem
> will be if we don't use log_cnt during sequence sync?
FWIW, I have argued two times at least that it should never be
necessary to expose log_cnt in the sequence meta-data: this is just a
counter to decide when a WAL record of a sequence should be generated.
If you are copying some sequence data over the wire on a new node in a
logical shape where WAL is independent, this counter is irrelevant:
you can just reset it. Please see also a83a944e9fdd.
--
Michael
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