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Re: increasing the default WAL segment size

Gavin Flower <gavinflower@archidevsys.co.nz>

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From: Gavin Flower <GavinFlower@archidevsys.co.nz>
To: Josh Berkus <josh@agliodbs.com>, Robert Haas <robertmhaas@gmail.com>, Magnus Hagander <magnus@hagander.net>
Cc: Simon Riggs <simon@2ndquadrant.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2016-08-25T22:45:25Z
Lists: pgsql-hackers 
On 26/08/16 05:43, Josh Berkus wrote:
> On 08/25/2016 01:12 PM, Robert Haas wrote:
>>> I agree that #4 is best. I'm not sure it's worth the cost. I'm not worried
>>>> at all about the risk of master/slave sync thing, per previous statement.
>>>> But if it does have performance implications, per Andres suggestion, then
>>>> making it configurable at initdb time probably comes with a cost that's not
>>>> worth paying.
>> At this point it's hard to judge, because we don't have any idea what
>> the cost might be.  I guess if we want to pursue this approach,
>> somebody will have to code it up and benchmark it.  But what I'm
>> inclined to do for starters is put together a patch to go from 16MB ->
>> 64MB.  Committing that early this cycle will give us time to
>> reconsider if that turns out to be painful for reasons we haven't
>> thought of yet.  And give tool authors time to make adjustments, if
>> any are needed.
> 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.

Currently, I'm not support pg in any production environment, and using 
it for testing & keeping up-to-date with pg.  So it would affect me - 
however, I have enough resources so it is no problem in practice.



Cheers,
Gavin

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.