Re: [Fwd: Index Advisor]

From: Kai-Uwe Sattler <kus(at)tu-ilmenau(dot)de>
To: Gurjeet Singh <singh(dot)gurjeet(at)gmail(dot)com>
Cc: "PGSQL Hackers" <pgsql-hackers(at)postgresql(dot)org>, "Gurjeet Singh" <gurjeet(dot)singh(at)enterprisedb(dot)com>
Subject: Re: [Fwd: Index Advisor]
Date: 2006-11-19 11:46:49
Message-ID: 27F0AB56-348F-4C89-B5F4-3F56A498F0EA@tu-ilmenau.de
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Hi,
Am 15.11.2006 um 15:34 schrieb Gurjeet Singh:
> =====
> .) The SELECTs in the pg_advise are returning wrong results, when
> the same index is suggested twice, because of the SUM() aggregates.
I don't think that this is a bug. If the same index is recommended
for two different queries it will appear two times in
pg_indexadvisor. So, if you want to calculate the overall benefit of
this index, then you have to sum up the local benefits for each query.

> .) I doubt that on a table t(a,b), for a suggestion of idx(b,a),
> pg_advise will
> suggest idx(a,b);
?? Not sure, if I understand you right. idx(b,a) and idx(a,b) are
completely different indexes. Why should pg_advise suggest idx(a,b).
But there is another bug: if there are recommendations like idx
(a,b,c), idx(a,b) and idx(a) it would be a good idea to create just
idx(a). I will add this to pg_advise as an optional feature.

Best,
Kai

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