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Re: BUG #4954: very slow query with 2 statements

From: Mikael Krantz <mk(at)zigamorph(dot)se>
To: Axel Fix <axel(dot)fix(at)sitqsystems(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #4954: very slow query with 2 statements
Date: 2009-07-29 15:20:15
Message-ID: 726863a30907290820p9a422f6ga7ff1d012e62d16f@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-bugs
This is not a bug. Each query requires a round-trip to the server so
it is natural that a lot of queries take additional time.

/M

On Wed, Jul 29, 2009 at 1:01 PM, Axel Fix<axel(dot)fix(at)sitqsystems(dot)com> wrote:
>
> The following bug has been logged online:
>
> Bug reference:      4954
> Logged by:          Axel Fix
> Email address:      axel(dot)fix(at)sitqsystems(dot)com
> PostgreSQL version: 8.3 and 8.4
> Operating system:   Windows XP
> Description:        very slow query with 2 statements
> Details:
>
> Hello,
>
> I have a simple er-model with 3 tables for 2D objects and use the following
> statements for query data:
>  s1 = "select t1.id,t1.type... from t0,t1
>      where t1.id_t0 = t0.id and t0.name='x1000'"
>  s2 = "select X,Y from t2 where id_t1=?"
>
> The table t1 returns 1000 elements which I iterate and use the returned id
> for the prepared statement s2. This way the server executes s2 1000 times.
> This seems to be very slow (>10sec!!! - the time grows with the whole number
> of datasets in the tables).
>
> Table t2 contains about 2.500 elements for the 1000 elements of t1.
>
> If I use a single statement, where I get an all in one result set, it will
> be finished after <100ms!
> The collected statement (with right table and column names) is:
> sc = "select t_graphobj.ID,type,fill,color,x,y\n" +
>     "  from t_graphdata,t_graphobj,t_names\n" +
>     " where ID_GRAPHOBJ=t_graphobj.ID\n" +
>     "   and t_graphobj.ID_NAMES=t_names.ID\n" +
>     "   and t_names.NAME='x1000'\n" +
>     " order by t_graphobj.id"
>
> If you need the java source code and SQL statements for the table, let me
> know.
>
> Thanks in advance,
>
> Axel Fix
>
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