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* slowness when subselect uses DISTINCT
@ 2007-04-18 18:16 Stuart McGraw <smcg2297@frii.com>
2007-04-18 22:43 ` Re: slowness when subselect uses DISTINCT Phillip Smith <phillip.smith@weatherbeeta.com.au>
0 siblings, 1 reply; 4+ messages in thread
From: Stuart McGraw @ 2007-04-18 18:16 UTC (permalink / raw)
To: pgsql-sql
I have several times now run into what seems
like similar performance problems with some
of my postgresql queries.
I have a view that runs reasonably quicky.
I use this view in a subselect in another
query and that query too runs reasonably
quicky.
The view returns some unwanted duplicate
rows so I modify it using either DISTINCT
or GROUP BY to eliminate them.
View still runs reasonably quickly.
I use the modified view as a subselect as
above, but now the query runs 2-3 orders
of magnitude more slowly than before.
Before I go through the effort of putting
together a specific and concise test case,
has anyone seen this general pattern and
have an explanation or advice? (PG-8.2.3)
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: slowness when subselect uses DISTINCT
2007-04-18 18:16 slowness when subselect uses DISTINCT Stuart McGraw <smcg2297@frii.com>
@ 2007-04-18 22:43 ` Phillip Smith <phillip.smith@weatherbeeta.com.au>
2007-04-19 14:20 ` Re: slowness when subselect uses DISTINCT Stuart McGraw <smcg2297@frii.com>
0 siblings, 1 reply; 4+ messages in thread
From: Phillip Smith @ 2007-04-18 22:43 UTC (permalink / raw)
To: 'Stuart McGraw' <smcg2297@frii.com>; pgsql-sql
May I suggest you post an EXPLAIN ANALYZE to the group for the query you're
having problems with...?
-----Original Message-----
From: pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-owner@postgresql.org]
On Behalf Of Stuart McGraw
Sent: Thursday, 19 April 2007 04:17
To: pgsql-sql@postgresql.org
Subject: [SQL] slowness when subselect uses DISTINCT
I have several times now run into what seems
like similar performance problems with some
of my postgresql queries.
I have a view that runs reasonably quicky.
I use this view in a subselect in another
query and that query too runs reasonably
quicky.
The view returns some unwanted duplicate
rows so I modify it using either DISTINCT
or GROUP BY to eliminate them.
View still runs reasonably quickly.
I use the modified view as a subselect as
above, but now the query runs 2-3 orders
of magnitude more slowly than before.
Before I go through the effort of putting
together a specific and concise test case,
has anyone seen this general pattern and
have an explanation or advice? (PG-8.2.3)
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^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: slowness when subselect uses DISTINCT
2007-04-18 18:16 slowness when subselect uses DISTINCT Stuart McGraw <smcg2297@frii.com>
2007-04-18 22:43 ` Re: slowness when subselect uses DISTINCT Phillip Smith <phillip.smith@weatherbeeta.com.au>
@ 2007-04-19 14:20 ` Stuart McGraw <smcg2297@frii.com>
2007-04-19 22:52 ` Re: slowness when subselect uses DISTINCT Phillip Smith <phillip.smith@weatherbeeta.com.au>
0 siblings, 1 reply; 4+ messages in thread
From: Stuart McGraw @ 2007-04-19 14:20 UTC (permalink / raw)
To: pgsql-sql
Phillip Smith wrote:
> May I suggest you post an EXPLAIN ANALYZE to the group for the query you're
> having problems with...?
I will do that but it has happened to me enough that it seems to be
a general pattern, not something specific to one of my queries,
so I thought some communal knowledge may exist. But apparently
not.
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: slowness when subselect uses DISTINCT
2007-04-18 18:16 slowness when subselect uses DISTINCT Stuart McGraw <smcg2297@frii.com>
2007-04-18 22:43 ` Re: slowness when subselect uses DISTINCT Phillip Smith <phillip.smith@weatherbeeta.com.au>
2007-04-19 14:20 ` Re: slowness when subselect uses DISTINCT Stuart McGraw <smcg2297@frii.com>
@ 2007-04-19 22:52 ` Phillip Smith <phillip.smith@weatherbeeta.com.au>
0 siblings, 0 replies; 4+ messages in thread
From: Phillip Smith @ 2007-04-19 22:52 UTC (permalink / raw)
To: 'Stuart McGraw' <smcg2297@frii.com>; pgsql-sql
Let's start with one, and whatever is causing it in one, is perhaps in
theory, causing the rest :)
Cheers,
~p
-----Original Message-----
From: pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-owner@postgresql.org]
On Behalf Of Stuart McGraw
Sent: Friday, 20 April 2007 00:20
To: pgsql-sql@postgresql.org
Subject: Re: [SQL] slowness when subselect uses DISTINCT
Phillip Smith wrote:
> May I suggest you post an EXPLAIN ANALYZE to the group for the query
you're
> having problems with...?
I will do that but it has happened to me enough that it seems to be
a general pattern, not something specific to one of my queries,
so I thought some communal knowledge may exist. But apparently
not.
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notify the sender by reply email.
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^ permalink raw reply [nested|flat] 4+ messages in thread
end of thread, other threads:[~2007-04-19 22:52 UTC | newest]
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2007-04-18 18:16 slowness when subselect uses DISTINCT Stuart McGraw <smcg2297@frii.com>
2007-04-18 22:43 ` Phillip Smith <phillip.smith@weatherbeeta.com.au>
2007-04-19 14:20 ` Stuart McGraw <smcg2297@frii.com>
2007-04-19 22:52 ` Phillip Smith <phillip.smith@weatherbeeta.com.au>
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