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From: Alexander Kuzmenkov <a.kuzmenkov@postgrespro.ru>
To: jesper.pedersen@redhat.com
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: pg@bowt.ie, Thomas Munro <thomas.munro@enterprisedb.com>
Cc: bhushan.uparkar@gmail.com, PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>
Subject: Re: Index Skip Scan
Date: Thu, 13 Sep 2018 22:36:24 +0300
Message-ID: <3cfd317e-2a8b-8681-0833-8f2ead3af4d4@postgrespro.ru> (raw)
In-Reply-To: <11b7c9d1-ae00-4385-97b2-fcd45f0a1a71@redhat.com>
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	<11b7c9d1-ae00-4385-97b2-fcd45f0a1a71@redhat.com>

El 13/09/18 a las 18:39, Jesper Pedersen escribió:
>
> Yes, this doesn't look good. Using your test case I'm seeing that 
> unique is being chosen when the group size is below 34, and skip 
> above. This is with the standard initdb configuration; did you change 
> something else ? Or did you force the default plan ?

Sorry I didn't mention this, the first column is indeed forced skip 
scan, just to see how it compares to index scan.

> This is something to look at -- maybe there is a way to use 
> btpo_next/btpo_prev instead/too in order to speed things up. Atm we 
> just have the scan key in BTScanOpaqueData. I'll take a look after my 
> upcoming vacation; feel free to contribute those changes in the 
> meantime of course.
>

I probably won't be able to contribute the changes, but I'll try to 
review them.

-- 
Alexander Kuzmenkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company





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