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Re: Inefficient query plan

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Jann Röder <roederja(at)ethz(dot)ch>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Inefficient query plan
Date: 2010-08-23 10:18:02
Message-ID: AANLkTi=9kbbKV0E0Jao6e7jBAZ1SB=QWKVxzotC_ZQ9R@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, Aug 23, 2010 at 4:15 AM, Jann Röder <roederja(at)ethz(dot)ch> wrote:
> Am 23.08.10 07:52, schrieb Scott Marlowe:
>> Also are a.indexid and b.indexid the same type?
>>
>
> You mean ItemID? Fields of the same name are of the same type - so yes.
> According to the documentation pgsql adds indexes for primary keys
> automatically so (b.itemID, b.indexNumber) is indexed. Or do you think
> adding an extra idnex for b.itemID alone will help? If I understand the
> documentation correctly, pqSQL can use the first column of a
> multi-column index as if it was indexed individually... but maybe I'm
> wrong here.

It can but that doesn't mean it will.  A multi-column index is often
quite a bit bigger than a single column one.

What happens if you try

set enable_seqscan=off;
(your query here)

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Subject: Re: Inefficient query plan
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