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Date: Mon, 14 Jul 2014 18:28:50 +0200
Subject: Re: Query Performance question
From: "Tomas Vondra" <tv@fuzzy.cz>
To: "Magers, James" <James.Magers@turner.com>
Cc: "Tomas Vondra" <tv@fuzzy.cz>, "Thomas Kellerer" <spam_eater@gmx.net>,
 "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
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On 14 Červenec 2014, 18:02, Magers, James wrote:
> Tomas,
>
> Thank you for the recommendation.  In this case, The bitmap scan runs
> quite quickly, however in production were data may or may not be cached
> and at higher volumes I am trying to ensure the process will continue to
> execute efficiently and reduce the impact of the process on other
> processes running against the database.

That's why it's important to do the testing with representative amount of
data. Testing the queries on significantly reduced dataset is pointless,
because the optimizer will do different decisions.

> My assessment is based on my experiences with the scans.  Does your
> experience provide you with a different assessment of the scan types and
> how efficient they may be?

No. Because I don't have your data. And it seems that your assessment is
based on experience with dataset that's very different from your expected
production dataset, which means the experience is not directly applicable.
The optimizer considers the size of the dataset when choosing the plan.

regards
Tomas


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