From: Jeremy Harris <jgh@wizmail.org>
To: pgsql-performance@postgresql.org
Subject: Re: Choice of bitmap scan over index scan
Date: Mon, 11 Jan 2010 19:41:08 +0000
Message-ID: <4B4B7ED4.8070208@wizmail.org> (raw)
In-Reply-To: <603c8f071001101853p6dd9517bofb7fcef43c97d79e@mail.gmail.com>
References: <d4468d971001100428v30236b55nb4cc82d216c7819e@mail.gmail.com>
<4B49DE7F.8080808@wizmail.org>
<603c8f071001101853p6dd9517bofb7fcef43c97d79e@mail.gmail.com>
On 01/11/2010 02:53 AM, Robert Haas wrote:
> On Sun, Jan 10, 2010 at 9:04 AM, Jeremy Harris<jgh@wizmail.org> wrote:
>> Needing to use an external (on-disk) sort method, when taking
>> only 90MB, looks odd.
[...]
> Well, you'd need to have work_mem> 90 MB for that not to happen, and
> very few people can afford to set that setting that high. If you have
> a query with three or four sorts using 90 MB a piece, and five or ten
> users running them, you can quickly kill the box...
Oh. That's, um, a real pity given the cost of going external. Any hope
of a more dynamic allocation of memory resource in the future?
Within a single query plan, the number of sorts is known; how about
a sort-mem limit per query rather than per sort (as a first step)?
Cheers,
Jeremy
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To: pgsql-performance@postgresql.org
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Subject: Re: Choice of bitmap scan over index scan
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