Date: Thu, 27 Oct 2016 07:38:38 +0200
From: Andreas Kretschmer <akretschmer@spamfence.net>
To: pgsql-performance@postgresql.org
Subject: Re: query slowdown after 9.0 -> 9.4 migration
Message-ID: <20161027053838.GA5952@tux>
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Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:

> On 10/26/2016 03:48 PM, Filip Rembiałkowski wrote:
>> Hi.
>>
>> Query run time degraded after migration from Pg 9.0 + postgis 1.5 to Pg
>> 9.4 + postgis 2.2.
>> EXPLAIN shows heap scan cost increase. What can be the reason for
>> 40-fold increase in page scans needed to run Bitmap Heap Scan with
>> Filter and Recheck?
>>
>
> On 9.0 the the scan accesses only 8 buffers:
>
> Buffers: shared hit=8
>
> while on 9.4 it has to inspect 316 of them:
>
> Buffers: shared hit=316

nice point ;-)


>
> Perhaps the table is organized / sorted differently, or something like  
> that. How did you do the upgrade?

Maybe table-bloat? Filip, check if autovacuum runs properly.


Regards, Andreas Kretschmer
-- 
Andreas Kretschmer
http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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