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Re: increasing the default WAL segment size

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Josh Berkus <josh@agliodbs.com>, Magnus Hagander <magnus@hagander.net>, Simon Riggs <simon@2ndquadrant.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2016-08-25T19:21:34Z
Lists: pgsql-hackers 
Robert Haas wrote:
> On Thu, Aug 25, 2016 at 2:49 PM, Alvaro Herrera
> <alvherre@2ndquadrant.com> wrote:

> > I think the relevant one for that case is the minimum, though:
> >
> > #min_wal_size = 80MB
> >
> > which corresponds to 5 segments.  I suppose the default value for this
> > minimum would change to some multiple of 64MB.
> 
> Yeah, Andres made the same point, although it looks like he
> erroneously stated that the minimum was 48MB whereas you have it as
> 80MB, which seems to be the actual value.  I assume we would have to
> raise that to either 128MB or 192MB, which does feel like a bit of a
> hefty increase.  It doesn't matter if you're going to make extensive
> use of the cluster, but if somebody's spinning up hundreds of clusters
> each of which has very little activity it might not be an altogether
> welcome change.

Yeah, and it's also related to the point Josh Berkus was making about
clusters with little activity.

Does it work to set the minimum to one WAL segment, i.e. 64MB?  guc.c
has a hardcoded minimum of 2, but I couldn't find an explanation for it.

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Make WAL segment size configurable at initdb time.

  2. Perform only one ReadControlFile() during startup.

  3. Introduce BYTES unit for GUCs.

  4. Remove useless duplicate inclusions of system header files.

  5. Refactor other replication commands to use DestRemoteSimple.

  6. Add a SHOW command to the replication command language.

  7. Add a new DestReceiver for printing tuples without catalog access.

  8. Support fls().

  9. Extend yesterday's patch making BLCKSZ and RELSEG_SIZE configurable to also

  10. Commit the reasonably uncontroversial parts of J.R. Nield's PITR patch, to

  11. XLOG (also known as WAL -:)) Bootstrap/Startup/Shutdown.

  12. Transaction log manager core code.