Skip site navigation (1) Skip section navigation (2)

Re: Major performance problem after upgrade from 8.3 to 8.4

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Gerhard Wiesinger <lists(at)wiesinger(dot)com>
Cc: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Andreas Kretschmer <akretschmer(at)spamfence(dot)net>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Major performance problem after upgrade from 8.3 to 8.4
Date: 2010-08-30 16:22:53
Message-ID: 11111.1283185373@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Gerhard Wiesinger <lists(at)wiesinger(dot)com> writes:
> I know the drawbacks of an EAV design but I don't want to discuss that. I 
> want to discuss the major performance decrease of PostgreSQL 8.3 
> (performance was ok) to PostgreSQL 8.4 (performance is NOT ok).

> Any further ideas how I can track this down?
> Can someone explain the difference in query plan from an optimizer point 
> of view?

Since you haven't shown us the 8.3 plan, it's kind of hard to speculate ;-)

One thing that jumped out at me was that 8.4 appears to be expecting
multiple matches in each of the left-joined tables, which is why the
total rowcount estimate balloons so fast.  I rather imagine that you are
expecting at most one match in reality, else the query isn't going to
behave nicely.  Is this correct?  Are you *sure* you analyzed all these
tables?  And if that is how the data looks, where is the actual
performance problem?  A bad rowcount estimate isn't in itself going
to kill you.

FWIW, in a similar albeit toy example, I don't see any difference
between the 8.3 and 8.4 plans or cost estimates.

			regards, tom lane

In response to

Responses

pgsql-performance by date

Next:From: Gerhard WiesingerDate: 2010-08-30 16:45:26
Subject: Re: Major performance problem after upgrade from 8.3 to 8.4
Previous:From: Gerhard WiesingerDate: 2010-08-30 16:11:36
Subject: Re: Major performance problem after upgrade from 8.3 to 8.4

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group