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Performance Problem Index Ignored, but why

From: "Thomas A(dot) Lowery" <tlowery(at)stlowery(dot)net>
To: pgsql-admin <pgsql-admin(at)postgresql(dot)org>
Subject: Performance Problem Index Ignored, but why
Date: 2002-05-22 04:02:05
Message-ID: 20020522000205.A17321@stllnx1.stlassoc.com (view raw or flat)
Thread:
Lists: pgsql-admin
I've the task of porting a current Oracle application to PostgreSQL.

Database: 7.2.1
OS: Linux 2.4.9-13smp

I've an odd thing happening with a query.  Using a simple table:

            Table "state_tst"
Column  |         Type         | Modifiers
---------+----------------------+-----------
id      | integer              | not null
v_state | character varying(2) |
f_state | character(2)         |
Indexes: st_f_state_idx,
	st_v_state_idx
Primary key: state_tst_pkey

id is a sequence number and primary key, v_state and f_state are 2
character U.S. States.  I created v_state as varchar(2) and f_state as
char(2) to test if the query explained/performed differently (it
doesn't).

CREATE INDEX st_v_state_idx ON state_tst USING btree (v_state);
CREATE INDEX st_f_state_idx ON state_tst USING btree (f_state);

Load the table using a copy from ...

vacuum verbose analyze state_tst;

Total rows: 14309241

Queries using either f_state = or v_state =  explain (and appear to
execute) using a sequential scan.  Resulting in 60 - 80 second query
times.

Can I force the use of an index?  Or do I have something wrong?  Any
ideas?

pg_test=# explain select  count(*) from state_tst where f_state = 'PA';
NOTICE:  QUERY PLAN:

Aggregate  (cost=277899.65..277899.65 rows=1 width=0)
  ->  Seq Scan on state_tst  (cost=0.00..277550.51 rows=139654
  width=0)

EXPLAIN

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Subject: Re: Performance Problem Index Ignored, but why
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Subject: port database to support japanese characters

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