Re: [HACKERS] Restricting maximum keep segments by repslots

From: Andres Freund <andres(at)anarazel(dot)de>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)lists(dot)postgresql(dot)org, thomas(dot)munro(at)enterprisedb(dot)com, sk(at)zsrv(dot)org, michael(dot)paquier(at)gmail(dot)com, peter(dot)eisentraut(at)2ndquadrant(dot)com
Subject: Re: [HACKERS] Restricting maximum keep segments by repslots
Date: 2018-07-31 19:14:03
Message-ID: 20180731191403.satjiy4i3ce3voqs@alap3.anarazel.de
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On 2018-07-31 15:11:52 -0400, Bruce Momjian wrote:
> On Tue, Jun 26, 2018 at 04:26:59PM +0900, Kyotaro HORIGUCHI wrote:
> > Hello. This is the reabased version of slot-limit feature.
> >
> > This patch limits maximum WAL segments to be kept by replication
> > slots. Replication slot is useful to avoid desync with replicas
> > after temporary disconnection but it is dangerous when some of
> > replicas are lost. The WAL space can be exhausted and server can
> > PANIC in the worst case. This can prevent the worst case having a
> > benefit from replication slots using a new GUC variable
> > max_slot_wal_keep_size.
>
> Have you considered just using a boolean to control if max_wal_size
> honors WAL preserved by replication slots, rather than creating the new
> GUC max_slot_wal_keep_size?

That seems like a bad idea. max_wal_size influences checkpoint
scheduling - there's no good reason to conflate that with retention?

Greetings,

Andres Freund

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