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BUG #4954: very slow query with 2 statements

From: "Axel Fix" <axel(dot)fix(at)sitqsystems(dot)com>
To: pgsql-bugs(at)postgresql(dot)org
Subject: BUG #4954: very slow query with 2 statements
Date: 2009-07-29 11:01:51
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-bugs
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


I have a simple er-model with 3 tables for 2D objects and use the following
statements for query data:
  s1 = "select,t1.type... from t0,t1
      where t1.id_t0 = and'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"

If you need the java source code and SQL statements for the table, let me

Thanks in advance,

Axel Fix


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