Horton

Re: [HACKERS] Restricting maximum keep segments by repslots

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Bruce Momjian <bruce@momjian.us>
Cc: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>, pgsql-hackers@lists.postgresql.org, thomas.munro@enterprisedb.com, sk@zsrv.org, michael.paquier@gmail.com, peter.eisentraut@2ndquadrant.com
Date: 2018-07-31T19:14:03Z
Lists: pgsql-hackers 
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

Commits

  1. Save slot's restart_lsn when invalidated due to size

  2. Fix checkpoint signalling

  3. Check slot->restart_lsn validity in a few more places

  4. Allow users to limit storage reserved by replication slots

  5. Remove header noise from test_decoding test

  6. Rework WAL-reading supporting structs

  7. Flip argument order in XLogSegNoOffsetToRecPtr