From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, 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 19:24:13 |
Message-ID: | 20180731192413.7lr4qbc4qbyoim5y@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2018-07-31 15:21:27 -0400, Stephen Frost wrote:
> Greetings,
>
> * Andres Freund (andres(at)anarazel(dot)de) wrote:
> > 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?
>
> I agree that we shouldn't conflate checkpointing and retention. What I
> wonder about though is what value will wal_keep_segments have once this
> new GUC exists..? I wonder if we could deprecate it...
Don't think that's a good idea. It's entirely conceivable to have a
wal_keep_segments much lower than max_slot_wal_keep_size. For some
throwaway things it can be annoying to have to slots, and if you remove
wal_keep_segments there's no alternative.
Greetings,
Andres Freund
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