Re: Synchronizing slots from primary to standby

From: Ajin Cherian <itsajin(at)gmail(dot)com>
To: shveta malik <shveta(dot)malik(at)gmail(dot)com>
Cc: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, "Drouvot, Bertrand" <bertranddrouvot(dot)pg(at)gmail(dot)com>, Peter Smith <smithpb2250(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: 2023-11-13 05:32:32
Message-ID: CAFPTHDZNV_HFAXULkaJOv_MMtLukCzDEgTaixxBwjEO_0Jg-kg@mail.gmail.com
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On Thu, Nov 9, 2023 at 9:54 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> PFA v32 patches which has below changes:
Testing with this patch, I see that if the failover enabled slot is
invalidated on the primary, then the corresponding synced slot is not
invalidated on the standby. Instead, I see that it continuously gets
the below error:
" WARNING: not synchronizing slot sub; synchronization would move it backwards"

In the code, I see that:
if (remote_slot->restart_lsn < MyReplicationSlot->data.restart_lsn)
{
ereport(WARNING,
errmsg("not synchronizing slot %s; synchronization
would move"
" it backwards", remote_slot->name));

ReplicationSlotRelease();
CommitTransactionCommand();
return;
}

If the restart_lsn of the remote slot is behind, then the
local_slot_update() function is never called to set the invalidation
status on the local slot. And for invalidated slots, restart_lsn is
always NULL.

regards,
Ajin Cherian
Fujitsu Australia

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