Re: low perfomances migrating from 9.3 to 9.5

2016-07-27 11:06 GMT+02:00 Michael Paquier <michael(dot)paquier(at)gmail(dot)com>:

> On Wed, Jul 27, 2016 at 5:54 PM, thomas veymont
> <thomas(dot)veymont(at)gmail(dot)com> wrote:
> > We switched from PostgreSQL server 9.3 to 9.5. From the very beginning
> there
> > was a noticeable drop in performances (for example : when injecting our
> SQL
> > dumps into 9.5, COPY and CREATE INDEX were very slow).
> >
> > Our configuration file was the same for 9.3 and 9.5, except for the
> > "chekpoint segment" that has been deprecated.
>
> Which value are you using for max_wal_size and min_wal_size? And which
> value of checkpoint_segments did you use previously? This could
> influence the checkpoint frequency.
> --
> Michael
>

in 9.3 we had :
checkpoint_segments = 128
#checkpoint_timeout = 5min # range 30s-1h
checkpoint_completion_target = 0.9 # checkpoint target duration, 0.0 - 1.0
#checkpoint_warning = 30s # 0 disables

as far as I remember these settings were for faster bulk loading.

in 9.5 we set:
max_wal_size = 6GB #
https://www.postgresql.org/docs/9.5/static/release-9-5.html, max_wal_size =
(3 * checkpoint_segments) * 16MB
#min_wal_size = 80MB

though I tried max_wal_size = 3GB (default is 1GB) and did not notice any
improvment.

cheers
tom