From: Alex Deucher <alexdeucher@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Merlin Moncure <mmoncure@gmail.com>
Cc: PostgreSQL Performance <pgsql-performance@postgresql.org>
Subject: Re: postgres 7.4 vs 8.x redux: query plans
Date: Tue, 3 Apr 2007 17:43:47 -0400
Message-ID: <a728f9f90704031443o7f2bfbbfy69439d069ccf5496@mail.gmail.com> (raw)
In-Reply-To: <12660.1175635265@sss.pgh.pa.us>
References: <a728f9f90704022209x1cd688f6pa9c8c2584376897e@mail.gmail.com>
<17931.1175578083@sss.pgh.pa.us>
<a728f9f90704030937t4855d730u41bd890de3d84603@mail.gmail.com>
<a728f9f90704031230y11451335i1a56fd8a7eba3a8e@mail.gmail.com>
<b42b73150704031313r3395d5fbi963857b8457b6fa6@mail.gmail.com>
<a728f9f90704031318l6471f6a3p3fc166b50031c213@mail.gmail.com>
<a728f9f90704031334x25bc8a60o991a476b774cc9fa@mail.gmail.com>
<12660.1175635265@sss.pgh.pa.us>
On 4/3/07, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> "Alex Deucher" <alexdeucher@gmail.com> writes:
> > Turning off bitmapscan ends up doing a sequential scan. Turning off
> > both bitmapscan and seqscan results in a bitmap heap scan. It doesn't
> > seem to want to use the index at all. Any ideas?
>
> The "ORed indexscans" plan style that was in 7.4 isn't there anymore;
> we use bitmap OR'ing instead. There actually are repeated indexscans
> hidden under the "= ANY" indexscan condition in 8.2, it's just that
> the mechanism for detecting duplicate matches is different. AFAIK the
> index access costs ought to be about the same either way, and the other
> costs the same or better as what we did in 7.4. It's clear though that
> 8.2 is taking some kind of big hit in the index access in your case.
> There's something very strange going on here.
>
> You do have both lc_collate and lc_ctype set to C, right? What about
> database encoding?
>
Also for reference, the old 7.4 DB is C for lc_collate and lc_ctype
and SQL_ASCII for encoding.
Alex
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: alexdeucher@gmail.com, tgl@sss.pgh.pa.us, mmoncure@gmail.com
Subject: Re: postgres 7.4 vs 8.x redux: query plans
In-Reply-To: <a728f9f90704031443o7f2bfbbfy69439d069ccf5496@mail.gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox