EXPLAIN ANALYZE much slower than running query normally - Mailing list pgsql-performance

From Chris Hutchinson
Subject EXPLAIN ANALYZE much slower than running query normally
Date
Msg-id IDEOKBCDGGIDOBADNGAPGEFEGBAA.chris@hutchinsonsoftware.com
Whole thread Raw
Responses Re: EXPLAIN ANALYZE much slower than running query normally  (Janning Vygen <vygen@gmx.de>)
Re: EXPLAIN ANALYZE much slower than running query normally  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-performance
Running a trivial query in v7.4.2 (installed with fedora core2) using
EXPLAIN ANALYZE is taking considerably longer than just running the query
(2mins vs 6 secs). I was using this query to quickly compare a couple of
systems after installing a faster disk.

Is this sort of slowdown to be expected?

Here's the query:
----------------------------------------
[chris@fedora tmp]$ time psql dbt << ENDSQL
> select count(*) from etab;
> ENDSQL
  count
---------
 9646782
(1 row)


real    0m6.532s
user    0m0.005s
sys     0m0.002s
[chris@fedora tmp]$ time psql dbt << ENDSQL
> explain analyze select count(*) from etab;
> ENDSQL
                                                       QUERY PLAN

----------------------------------------------------------------------------
---------------
-----------------------------
 Aggregate  (cost=182029.78..182029.78 rows=1 width=0) (actual
time=112701.488..112701.493
rows=1 loops=1)
   ->  Seq Scan on etab  (cost=0.00..157912.82 rows=9646782 width=0) (actual
time=0.053..578
59.120 rows=9646782 loops=1)
 Total runtime: 112701.862 ms
(3 rows)


real    1m52.716s
user    0m0.003s
sys     0m0.005s
---------------------------------------

Thanks in advance for any clues.

Chris Hutchinson


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