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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: Gavin Flower <GavinFlower@archidevsys.co.nz>
Cc: Josh Berkus <josh@agliodbs.com>, Robert Haas <robertmhaas@gmail.com>, Magnus Hagander <magnus@hagander.net>, Simon Riggs <simon@2ndquadrant.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2016-08-26T03:37:06Z
Lists: pgsql-hackers 
Gavin Flower wrote:
> On 26/08/16 05:43, Josh Berkus wrote:

> >The one thing I'd be worried about with the increase in size is folks
> >using PostgreSQL for very small databases.  If your database is only
> >30MB or so in size, the increase in size of the WAL will be pretty
> >significant (+144MB for the base 3 WAL segments).  I'm not sure this is
> >a real problem which users will notice (in today's scales, 144MB ain't
> >much), but if it turns out to be, it would be nice to have a way to
> >switch it back *just for them* without recompiling.
> >
> Let such folk use Microsoft Access???  <Ducks & runs away very fast!>
> 
> 
> More seriously:
> Surely most such people would be using very old hardware & not likely to be
> upgrading to the most recent version of pg in the near future?  And for the
> ones using modern hardware: either they have enough resources not to notice,
> or very probably will know enough to hunt round for a way to reduce the WAL
> size - I strongly suspect.

I've seen people with unusual environments, such as running Pg in some
embedded platform with minimal resources, where they were baffled that
Postgres used so much disk space on files that were barely written to
and never read.  It wasn't a question of there being "large" drives to
buy, but one of not wanting to have a drive in the first place.  Now, I
grant that this was a few years ago already and disk tech (SSDs) has
changed that world; maybe that argument doesn't apply anymore.

-- 
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.