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Re: increasing the default WAL segment size

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2016-08-25T03:52:20Z
Lists: pgsql-hackers 
On 2016-08-24 23:26:51 -0400, Robert Haas wrote:
> On Wed, Aug 24, 2016 at 10:54 PM, Andres Freund <andres@anarazel.de> wrote:
> > and I'm also rather doubtful that it's actually without overhead.
> 
> Really?  Where do you think the overhead would come from?

ATM we do a math involving XLOG_BLCKSZ in a bunch of places (including
doing a lot of %). Some of that happens with exclusive lwlocks held, and
some even with a spinlock held IIRC. Making that variable won't be
free. Whether it's actually measurabel - hard to say. I do remember
Heikki fighting hard to simplify some parts of the critical code during
xlog scalability stuff, and that that even involved moving minor amounts
of math out of critical sections.

> What sort of test would you run to try to detect it?

Xlog scalability tests (parallel copy, parallel inserts...), and
decoding speed (pg_xlogdump --stats?)

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.