Re: RE: Re: [ADMIN] v7.1b4 bad performance

Lincoln Yeoh wrote:
> 
> Just another data point.
> 
> I downloaded a snapshot yesterday - Changelogs dated Feb 20 17:02
> 
> It's significantly slower than "7.0.3 with fsync off" for one of my webapps.
> 
> 7.0.3 with fsync off gets me about 55 hits per sec max (however it's
> interesting that the speed keeps dropping with continued tests).
> ( PostgreSQL 7.0.3 on i686-pc-linux-gnu, compiled by gcc egcs-2.91.66)
> 
> For 7.1b4 snapshot I get about 23 hits per second (drops gradually too).
> I'm using Pg::DBD compiled using the 7.1 libraries for both tests.
> (PostgreSQL 7.1beta4 on i686-pc-linux-gnu, compiled by GCC egcs-2.91.66)
> 
> For a simple "select only" webapp I'm getting 112 hits per sec for 7.0.3.
> and 109 hits a sec for the 7.1 beta4 snapshot. These results remain quite
> stable over many repeated tests.
> 
> The first webapp does a rollback, begin, select, update, commit, begin, a
> bunch of selects in sequence and rollback.

It may be that WAL has changed the rollback time-characteristics to
worse 
than pre-wal ?

If that is the case tha routeinely rollbacking transactions is no longer 
a good programming practice.

It may have used to be as I think that before wal both rollback and
commit 
had more or less the same cost.

> So my guess is that the 7.1 updates (with default fsync) are significantly
> slower than 7.0.3 fsync=off now.

the consensus seems to be that they are only "a little" slower.

> But it's interesting that the updates slow things down significantly. Going
> from 50 to 30 hits per second after a few thousand hits for 7.0.3, and 23
> to 17 after about a thousand hits for 7.1beta4.
> 
> For postgresql 7.0.3 to speed things back up from 30 to 60 hits per sec I
> had to do:

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Hannu