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Re: increasing the default WAL segment size

Simon Riggs <simon@2ndquadrant.com>

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From: Simon Riggs <simon@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Simon Riggs <simon@2ndquadrant.com>, Amit Kapila <amit.kapila16@gmail.com>, Jim Nasby <Jim.Nasby@bluetreble.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Beena Emerson <memissemerson@gmail.com>
Date: 2017-01-03T16:16:37Z
Lists: pgsql-hackers 
On 3 January 2017 at 15:44, Robert Haas <robertmhaas@gmail.com> wrote:

> Yeah.  I don't think there's any way to get around the fact that there
> will be bigger latency spikes in some cases with larger WAL files.

One way would be for the WALwriter to zerofill new files ahead of
time, thus avoiding the latency spike.

> For example, in a quick test on my laptop,
> zero-filling a 16 megabyte file using "dd if=/dev/zero of=x bs=8k
> count=2048" takes about 11 milliseconds, and zero-filling a 64
> megabyte file with a count of 8192 increases the time to almost 50
> milliseconds.  That's something, but I wouldn't rate it as concerning.

I would rate that as concerning, especially if we allow much larger sizes.

> But the flip side is that it's wrong to imagine that there's no harm
> in leaving the situation as it is.

The case for change has been made; the only discussion is what's in
the new patch.

-- 
Simon Riggs                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.