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Re: increasing the default WAL segment size

Beena Emerson <memissemerson@gmail.com>

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From: Beena Emerson <memissemerson@gmail.com>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Amit Kapila <amit.kapila16@gmail.com>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Stephen Frost <sfrost@snowman.net>, David Steele <david@pgmasters.net>, tushar <tushar.ahuja@enterprisedb.com>, Prabhat Sahu <prabhat.sahu@enterprisedb.com>, Ashutosh Sharma <ashu.coek88@gmail.com>, Jim Nasby <Jim.Nasby@bluetreble.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>
Date: 2017-04-06T11:13:51Z
Lists: pgsql-hackers 
Hello,

On Wed, Apr 5, 2017 at 4:59 PM, Simon Riggs <simon@2ndquadrant.com> wrote:

> On 5 April 2017 at 06:04, Beena Emerson <memissemerson@gmail.com> wrote:
>
> I see various issues raised but not properly addressed
>
> 1. we would need to drop support for segment sizes < 16MB unless we
> adopt a new incompatible filename format.
> I think at 16MB the naming should be the same as now and that
> WALfilename -> LSN is very important.
> For this release, I think we should just allow >= 16MB and avoid the
> issue thru lack of time.
>
> 2. It's not clear to me the advantage of being able to pick varying
> filesizes. I see great disadvantage in having too many options, which
> greatly increases the chance of incompatibility, annoyance and
> breakage. I favour a small number of values that have been shown by
> testing to be sweet spots in performance and usability. (1GB has been
> suggested)
>

Does the options 16, 64 and 1024 seem good.
We can remove sizes below 16 as most have agreed and as per the discussion,
64MB and 1GB seems favoured. We could probably allow 32MB since it was an
already allowed size?


> 3. New file allocation has been a problem raised with this patch for
> some months now.
>

This did not seem to be an open issue, at least there was not many
disagreements. Higher the server load, more WAL generated. For the same
load, the frequency of file allocation reduces for higher wal-segsize
values. Overall it is either filling up many files or few larger files.

-- 

Beena Emerson

EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.