Re: Logical replication wal sender timestamp bug

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Logical replication wal sender timestamp bug
Date: 2019-11-06 07:15:00
Message-ID: 20191106071500.GH1604@paquier.xyz
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On Tue, Nov 05, 2019 at 01:19:37PM +0900, Michael Paquier wrote:
> On Sat, Nov 02, 2019 at 09:54:54PM -0400, Jeff Janes wrote:
>> Filling out the timestamp after the message has already been sent is taking
>> "as late as possible" a little too far. It results in every message having
>> a zero timestamp, other than keep-alives which go through a different path.
>
> It seems to me that you are right: the timestamp is computed too
> late.

It is easy enough to reproduce the problem by setting for example
logical replication between two nodes and pgbench to produce some
load and then monitor pg_stat_subscription periodically. However, it
is a problem since logical decoding has been introduced (5a991ef) so
committed your fix down to 9.4.
--
Michael

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