On 4/5/17 06:04, Beena Emerson wrote:
>     I suggest the next step is to dial up the allowed segment size in
>     configure and run some tests about what a reasonable maximum value could
>     be.  I did a little bit of that, but somewhere around 256 MB, things got
>     really slow.
> Would it be better if just increase the limit to 128MB for now?
> In next we can change the WAL file name format and expand the range?

I don't think me saying it felt a bit slow around 256 MB is a proper
technical analysis that should lead to the conclusion that that upper
limit should be 128 MB. ;-)

This tells me that there is a lot of explore and test here before we
should let it loose on users.

I think the best we should do now is spend a bit of time exploring
whether/how larger values of segment size behave, and bump the hardcoded
configure limit if we get positive results.  Everything else should
probably be postponed.

(Roughly speaking, to get started, this would mean compiling with
--with-wal-segsize 16, 32, 64, 128, 256, run make check-world both
sequentially and in parallel, and take note of a) passing, b) run time,
c) disk space.)

Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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