Date: Mon, 28 Aug 2023 02:44:48 +0000
From: Victor Sudakov <vas@sibptus.ru>
To: pgsql-admin@lists.postgresql.org
Subject: Re: Temporary disabling a replica in a Patroni cluster
Message-ID: <ZOwKIAAr2cpNUOY6@admin.sibptus.ru>
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Victor Sudakov wrote:
> 
> Do you perchance know what is the correct procedure of temporarily
> taking down a replica in a Patroni cluster, e.g. for 5-10 minutes of
> hardware maintenance?
> 
> The problem is that after stopping the patroni process (service) on a
> replica, patroni removes the corresponding physical replication slot
> from the leader, and unless the wal_keep_size value is unsanely high,
> the replica, when up again, cannot restart streaming because the WAL
> segments are already gone from the leader.
> 
> Well, you all know:
> <%%%>LOG:  started streaming WAL from primary at B4A0/E2000000 on timeline 8
> <%%%>FATAL:  could not receive data from WAL stream: ERROR:  requested WAL segment 000000080000B4A0000000E2 has already been removed
> <%%%>LOG:  waiting for WAL to become available at B4A0/E2002000
> 
> Do you think there is a way to tell Patroni that a replica is down
> temporarily and its replication slot should not be removed?
> 
> Or, what am I missing? 

As WAL archiving (wal-g) is enabled in this cluster anyway, do you
think adding "postgresql.parameters.restore_command" to the Patroni
config will help in this situation? 

restore_command works very well in regular Postgres clusters catching
up from a big replication delay and permits to have wal_keep_size=0,
however does anyone know if there are any Patroni-specific reasons not
to use restore_command under Patroni?

-- 
Victor Sudakov VAS4-RIPE
http://vas.tomsk.ru/
2:5005/49@fidonet