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From: Josh Berkus <josh@agliodbs.com>
To: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
To: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: Strange choice of general index over partial index
Date: Fri, 16 Jan 2015 16:28:34 +1300
Message-ID: <54B88562.4040500@agliodbs.com> (raw)
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On 01/16/2015 04:17 PM, Mark Kirkwood wrote:
> On 16/01/15 16:06, Mark Kirkwood wrote:
> 
>> A bit more poking about shows that the major factor (which this fake
>> dataset anyway) is the default for effective_cache_size (changes from
>> 128MB to 4GB in 9.4). Increasing this makes 9.2 start using the
>> files_in_flight index in a plain index scan too.
>>
> 
> Arrg - misread the planner output....in 9.2 what changes is a plan that
> uses an index scan on the *file_state* index (not
> files_in_flight)...which appears much faster than the bitmap scan on
> file_state. Apologies for the confusion.
> 
> I'm thinking that I'm seeing the effect Tom has just mentioned.

It's not using a bitmapscan in either case; it's a straight indexscan.


-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com


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