From: Cédric Villemain <cedric@2ndquadrant.com>
To: pgsql-performance@postgresql.org
Cc: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Marc Mamin <M.Mamin@intershop.de>
Cc: Jesper Krogh <jesper@krogh.cc>
Cc: Maxim Boguk <maxim.boguk@gmail.com>
Subject: Re: Performance of a large array access by position (tested version 9.1.3)
Date: Thu, 28 Jun 2012 12:22:35 +0200
Message-ID: <201206281222.45642.cedric@2ndquadrant.com> (raw)
In-Reply-To: <CAFj8pRCddmsCZFJgEG5zqGd5wj3RuhODJKD4SLpdT5gnfdrEGw@mail.gmail.com>
References: <CAK-MWwQxjfug8CqBjQXQJJQLQ2bb5kcagEm4GwFvVTgHkLuSBA@mail.gmail.com>
<C4DAC901169B624F933534A26ED7DF310861B5E9@JENMAIL01.ad.intershop.net>
<CAFj8pRCddmsCZFJgEG5zqGd5wj3RuhODJKD4SLpdT5gnfdrEGw@mail.gmail.com>
> >> >>> Is that behaviour is correct?
> >>
> >> yes - access to n position means in postgresql - skip n-1 elements
> >
> > Hmmm...
> >
> > how many elements to be skipped here ?
>
> there are two independent stages:
>
> a) detoast - loading and decompression (complete array is detoasted)
> b) access
>
> if you has very large arrays, then @a is significant
There is a place to add PG_GETARG_ARRAY_P_SLICE. The code is just not done
yet.
--
Cédric Villemain +33 (0)6 20 30 22 52
http://2ndQuadrant.fr/
PostgreSQL: Support 24x7 - Développement, Expertise et Formation
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To: pgsql-performance@postgresql.org
Cc: cedric@2ndquadrant.com, pavel.stehule@gmail.com, M.Mamin@intershop.de, jesper@krogh.cc, maxim.boguk@gmail.com
Subject: Re: Performance of a large array access by position (tested version 9.1.3)
In-Reply-To: <201206281222.45642.cedric@2ndquadrant.com>
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