Re: pg_receivewal starting position

From: Ronan Dunklau <ronan(dot)dunklau(at)aiven(dot)io>
To: Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Ronan Dunklau <ronan(dot)dunklau(at)aiven(dot)io>
Cc: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Subject: Re: pg_receivewal starting position
Date: 2021-08-26 12:14:27
Message-ID: 2396633.4C23JXgCg5@aivenronan
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Le jeudi 29 juillet 2021, 11:09:40 CEST Ronan Dunklau a écrit :
> Patch 0001 adds the new READ_REPLICATION_SLOT command.
> It returns for a given slot the type, restart_lsn, flush_lsn,
> restart_lsn_timeline and flush_lsn_timeline.
> The timelines are determined by reading the current timeline history, and
> finding the timeline where we may find the record. I didn't find explicit
> test for eg IDENTIFY_SYSTEM so didn't write one either for this new
> command, but it is tested indirectly in patch 0002.
> Patch 0002 makes pg_receivewal use that command if we use a replication slot
> and the command is available, and use the restart_lsn and
> restart_lsn_timeline as a starting point. It also adds a small test to
> check that we start back from the previous restart_lsn instead of the
> current flush position when our destination directory does not contain any
> WAL file.
> I also noticed we don't test following a timeline switch. It would probably
> be good to add that, both for the case where we determine the previous
> timeline from the archived segments and when it comes from the new command.
> What do you think ?

Following the discussion at [1], I refactored the implementation into
streamutil and added a third patch making use of it in pg_basebackup itself in
order to fail early if the replication slot doesn't exist, so please find
attached v2 for that.

Best regards,


Ronan Dunklau

Attachment Content-Type Size
v2-0001-Add-READ_REPLICATION_SLOT-command.patch text/x-patch 10.8 KB
v2-0002-Use-READ_REPLICATION_SLOT-command-in-pg_receivewa.patch text/x-patch 8.3 KB
v2-0003-Check-slot-existence-in-pg_basebackup.patch text/x-patch 2.2 KB

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