From: | Sergei Kornilov <sk(at)zsrv(dot)org> |
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To: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>, Bernd Helmle <mailings(at)oopsware(dot)de>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Optimization of vacuum for logical replication |
Date: | 2019-08-21 11:07:51 |
Message-ID: | 1347121566385671@iva1-9be92bdead40.qloud-c.yandex.net |
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Lists: | pgsql-hackers |
Hello
> Also I can't believe that DBA which explicitly sets wal_level is set to
> logical will use streaming replication without associated replication slot.
I am.
> Yes, it is possible to have physical replica withotu replication slot.
> But it is not safe, because there is always a risk that lag between
> master and replica becomes larger than size of WAL kept at master.
Just an example: replica for manual queries, QA purposes or for something else that is not an important part of the system.
If I use replication slots - my risk is out-of-space on primary and therefore shutdown of primary. With downtime for application.
If I use wal_keep_segments instead - I have some limited (and usually stable) amount of WAL but risk to have outdated replica.
I prefer to have an outdated replica but primary is more safe. Its OK for me to just take fresh pg_basebackup from another replica.
And application want to use logical replication so wal_level = logical.
If we not want support such usecase - we need explicitly forbid replication without replication slots.
regards, Sergei
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