| 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 |
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| 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
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