Re: Strange Create Index behaviour

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Gary Doades <gpd(at)gpdnet(dot)co(dot)uk>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Strange Create Index behaviour
Date: 2006-02-15 23:51:21
Message-ID: 1140047481.12131.205.camel@localhost.localdomain
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-hackers pgsql-performance

On Wed, 2006-02-15 at 16:51 -0500, Tom Lane wrote:
> Gary Doades <gpd(at)gpdnet(dot)co(dot)uk> writes:
> > Interestingly, if I don't delete the table after a run, but just drop
> > and re-create the index repeatedly it stays a pretty consistent time,
> > either repeatedly good or repeatedly bad!
>
> This is consistent with the theory of a data-dependent performance
> problem in qsort. If you don't generate a fresh set of random test
> data, then you get repeatable runtimes. With a new set of test data,
> you might or might not hit the not-so-sweet-spot that we seem to have
> detected.

Agreed. Good analysis...

Best Regards, Simon Riggs

In response to

Browse pgsql-hackers by date

  From Date Subject
Next Message Gary Doades 2006-02-15 23:55:30 Re: qsort again (was Re: [PERFORM] Strange Create Index behaviour)
Previous Message Tom Lane 2006-02-15 23:40:22 Re: patch fixing the old RETURN NEXT bug

Browse pgsql-performance by date

  From Date Subject
Next Message Gary Doades 2006-02-15 23:55:30 Re: qsort again (was Re: [PERFORM] Strange Create Index behaviour)
Previous Message Tom Lane 2006-02-15 23:28:29 qsort again (was Re: [PERFORM] Strange Create Index behaviour)