Re: Choice of bitmap scan over index scan - Mailing list pgsql-performance

From Jeremy Harris
Subject Re: Choice of bitmap scan over index scan
Date
Msg-id 4B4B7ED4.8070208@wizmail.org
Whole thread Raw
In response to Re: Choice of bitmap scan over index scan  (Robert Haas <robertmhaas@gmail.com>)
Responses Re: Choice of bitmap scan over index scan
List pgsql-performance
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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