Re: select query takes 13 seconds to run with index

On Mon, May 26, 2008 at 4:26 PM, Justin <justin(at)emproshunts(dot)com> wrote:
> mark wrote:
>> Hi, is there anyway this can be made faster? id is the primary key,
>> and there is an index on uid..
>> thanks
>> EXPLAIN ANALYZE select * from pokes where uid = 578439028 order by id
>> DESC limit 6;
>> QUERY
>> PLAN
>>
>> ----------------------------------------------------------------------------------------------------------------------------------------------------
>> Limit (cost=0.00..9329.02 rows=6 width=135) (actual
>> time=13612.247..13612.247 rows=0 loops=1)
>> -> Index Scan Backward using pokes_pkey on pokes
>> (cost=0.00..5182270.69 rows=3333 width=135) (actual
>> time=13612.245..13612.245 rows=0 loops=1)
>> Filter: (uid = 578439028)
>> Total runtime: 13612.369 ms
>> (4 rows)
> First this should be posted on performance list.
sorry about this.

> how many records are in this table?
22334262, 22 million records.

> The estimate is way off, when was the last time Vaccum was on the table?
about a week ago i ran this VACUUM VERBOSE ANALYZE;
this table is never updated or deleted, rows are just inserted...

> What verison of Postgresql are you running
8.3.1

> Size of the Table
22 million rows approximately

> Table layout
CREATE TABLE pokes
(
id serial NOT NULL,
uid integer,
action_id integer,
created timestamp without time zone DEFAULT now(),
friend_id integer,
message text,
pic text,
"name" text,
CONSTRAINT pokes_pkey PRIMARY KEY (id)
)
WITH (OIDS=FALSE);
ALTER TABLE pokes OWNER TO postgres;

-- Index: idx_action_idx

-- DROP INDEX idx_action_idx;

CREATE INDEX idx_action_idx
ON pokes
USING btree
(action_id);

-- Index: idx_friend_id

-- DROP INDEX idx_friend_id;

CREATE INDEX idx_friend_id
ON pokes
USING btree
(friend_id);

-- Index: idx_pokes_uid

-- DROP INDEX idx_pokes_uid;

CREATE INDEX idx_pokes_uid
ON pokes
USING btree
(uid);

> Load on the database
how do i measure load on database?