Re: Optimizing a query

Your nap and nxx columns have character datatype, so you should use
quotes. Try:

        explain analyze  select * from nanpa where npa='775' and
nxx='473';

If that does not work, you could try to influence the planner's
execution plan to favor index scans over sequential scan by tweaking a
couple of the postgres parameters, particularly, the
effective_cache_size. This parameter primarily set the planner's
estimates of the relative likelihood of a particular table or index
being in memory, and will thus have a significant effect on whether the
planner chooses indexes over seqscans. Tweaking such parameters are
usually done as a last resort.

--
  Husam

-----Original Message-----
From: pgsql-performance-owner@postgresql.org
[mailto:pgsql-performance-owner@postgresql.org] On Behalf Of James Cloos
Sent: Wednesday, December 13, 2006 2:35 PM
To: Tomeh, Husam
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Optimizing a query

>>>>> "Husam" == Tomeh, Husam <htomeh@firstam.com> writes:

Husam> Have you run vacuum/analyze on the table?

Yes, back when I first noticed how slow it was.
It did not make any difference.

explain analyze says:

,----
| n=# explain analyse  select * from nanpa where npa=775 and nxx=473;
|                                                QUERY PLAN

|
------------------------------------------------------------------------
--------------------------------
|  Seq Scan on nanpa  (cost=0.00..5344.60 rows=4 width=105) (actual
time=371.718..516.816 rows=1 loops=1)
|    Filter: (((npa)::text = '775'::text) AND ((nxx)::text =
'473'::text))
|  Total runtime: 516.909 ms
| (3 rows)
`----

vs:

,----
| n=# explain analyse  select * from nanpa where npa=775::char and
nxx=473::char;
|                                                       QUERY PLAN

|
------------------------------------------------------------------------
----------------------------------------------
|  Index Scan using nanpa_pkey on nanpa  (cost=0.00..4.33 rows=1
width=105) (actual time=64.831..64.831 rows=0 loops=1)
|    Index Cond: ((npa = '7'::bpchar) AND (nxx = '4'::bpchar))
|  Total runtime: 64.927 ms
| (3 rows)
`----

BTW, I forgot to mention I'm at 8.1.4 on that box.

-JimC
--
James Cloos <cloos@jhcloos.com>         OpenPGP: 1024D/ED7DAEA6

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