Re: any way to use indexscan to get last X values

On 16 Jun 2003 at 0:37, Tomaz Borstnar wrote:
>
> krtjavendan34=> EXPLAIN ANALYZE SELECT thread, modifystamp, count(id) AS
> tcount,abstime(modifystamp) AS latest, max(id) as maxid FROM tjavendan
> WHERE approved='Y' GROUP BY modifystamp, thread ORDER BY modifystamp desc,
> thread desc limit 40;
> QUERY
> PLAN
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> Limit (cost=0.00..97.13 rows=40 width=12) (actual time=1.07..48.71
> rows=40 loops=1)
> -> Aggregate (cost=0.00..20947.38 rows=8626 width=12) (actual
> time=1.05..48.23 rows=41 loops=1)
> -> Group (cost=0.00..20516.06 rows=86265 width=12) (actual
> time=0.35..42.25 rows=843 loops=1)
> -> Index Scan Backward using tjavendan_modstamp_thrd on
> tjavendan (cost=0.00..20084.73 rows=86265 width=12) (actual
> time=0.34..31.29 rows=844 loops=1)
> Filter: (approved = 'Y'::bpchar)
> Total runtime: 50.20 msec
> (6 rows)
>
> Used to be between 5800 and 6741 msec before this patch!

Good that the patch works for you. But as I see there is an improvement in
plan. Not nitpicking but what does actual performance difference between system
before patch and after patch?

Bye
Shridhar

--
QOTD: "In the shopping mall of the mind, he's in the toy department."