Re: Major differences between oracle and postgres performance

From: Shridhar Daithankar <shridhar(at)frodo(dot)hserus(dot)net>
To: Gary Cowell <gary_cowell(at)yahoo(dot)co(dot)uk>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Major differences between oracle and postgres performance
Date: 2004-06-18 12:17:55
Message-ID: 40D2DD73.7070600@frodo.hserus.net
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Gary Cowell wrote:
> The explain output on postgres shows the same
> execution with a scan on vers and a sort but the query
> time is 78.6 seconds.
>
> The explain output from PostgreSQL is:
> QUERY PLAN
> ---------------------------------------------------------------------------------
> Unique (cost=117865.77..120574.48 rows=142
> width=132)
> -> Sort (cost=117865.77..119220.13 rows=541741
> width=132)
> Sort Key: "version"
> -> Seq Scan on vers (cost=0.00..21367.41
> rows=541741 width=132)
> Filter: ("version" IS NOT NULL)
>
> I do have an index on the column in question but
> neither oracle nor postgresql choose to use it (which
> given that we're visiting all rows is perhaps not
> surprising).

Can you post explain analyze for the same query? It contains actual numbers
alond side the chosen plan.

>
> I'm not as familiar with postgresql as I am with
> Oracle but I think I've configured comparible
> buffering and sort area sizes, certainly there isn't
> much physical IO going on in either case.

Well, for postgresql you should check out

http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html
http://www.varlena.com/varlena/GeneralBits/Tidbits/annotated_conf_e.html

HTH

Shridhar

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