From: Petr Jelinek <petr.jelinek@2ndquadrant.com>
To: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
To: pgsql-hackers@postgresql.org
Subject: Re: Restricting maximum keep segments by repslots
Date: Tue, 28 Feb 2017 05:27:05 +0100
Message-ID: <33bcf803-4aa8-27b6-b6bd-4fb3ae950b19@2ndquadrant.com> (raw)
In-Reply-To: <20170228.122736.123383594.horiguchi.kyotaro@lab.ntt.co.jp>
References: <20170228.122736.123383594.horiguchi.kyotaro@lab.ntt.co.jp>
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On 28/02/17 04:27, Kyotaro HORIGUCHI wrote:
> Hello.
>
> Although replication slot is helpful to avoid unwanted WAL
> deletion, on the other hand it can cause a disastrous situation
> by keeping WAL segments without a limit. Removing the causal
> repslot will save this situation but it is not doable if the
> standby is active. We should do a rather complex and forcible
> steps to relieve the situation especially in an automatic
> manner. (As for me, specifically in an HA cluster.)
>
I agree that that it should be possible to limit how much WAL slot keeps.
> This patch adds a GUC to put a limit to the number of segments
> that replication slots can keep. Hitting the limit during
> checkpoint shows a warining and the segments older than the limit
> are removed.
>
>> WARNING: restart LSN of replication slots is ignored by checkpoint
>> DETAIL: Some replication slots lose required WAL segnents to continue.
>
However this is dangerous as logical replication slot does not consider
it error when too old LSN is requested so we'd continue replication,
hiding data loss.
--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: petr.jelinek@2ndquadrant.com, horiguchi.kyotaro@lab.ntt.co.jp
Subject: Re: Restricting maximum keep segments by repslots
In-Reply-To: <33bcf803-4aa8-27b6-b6bd-4fb3ae950b19@2ndquadrant.com>
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