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Re: increasing the default WAL segment size

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Jim Nasby <Jim.Nasby@bluetreble.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Beena Emerson <memissemerson@gmail.com>
Date: 2017-01-03T13:45:31Z
Lists: pgsql-hackers 
On Tue, Jan 3, 2017 at 6:41 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On 2 January 2017 at 21:23, Jim Nasby <Jim.Nasby@bluetreble.com> wrote:
>
>> It's not clear from the thread that there is consensus that this feature is desired. In particular, the performance aspects of changing segment size from a C constant to a variable are in question. Someone with access to large hardware should test that. Andres[1] and Robert[2] did suggest that the option could be changed to a bitshift, which IMHO would also solve some sanity-checking issues.
>
> Overall, Robert has made a good case. The only discussion now is about
> the knock-on effects it causes.
>
> One concern that has only barely been discussed is the effect of
> zero-ing new WAL files. That is a linear effect and will adversely
> effect performance as WAL segment size increases.
>

Sorry, but I am not able to understand why this is a problem?  The
bigger the size of WAL segment, lesser the number of files.  So IIUC,
then it can only impact if zero-ing two 16MB files is cheaper than
zero-ing one 32MB file.  Is that your theory or you have something
else in mind?


-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

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.