Re: select query takes 13 seconds to run with index

On Mon, May 26, 2008 at 4:49 PM, Justin <justin@emproshunts.com> wrote:
> mark wrote:
>
> On Mon, May 26, 2008 at 4:26 PM, Justin <justin@emproshunts.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
>
>
> I have no experience  on large datasets so people with more experience in
> this area are going to have to chime in.
> My gut feel is 13 seconds for Postgresql to sort through an index of that
> size and table is not bad.
>
> you may need to take a look at hardware and postgresql.config settings to
> improve the performance for this query
>
> This query is very simple where changing it around or adding index results
> massive improvements is not going to help in this case.
the hardware is e5405 dual quad core on a 16GB RAM machine, with 8.3.1
default settings except maximum connections increased...