Re: Reason of Slowness of query

23.03.11 09:30, Adarsh Sharma ???????(??):
> Thanks Chetan, here is the output of your updated query :
>
>
> *explain select distinct(p.crawled_page_id) from page_content p where
> NOT EXISTS (select 1 from clause2 c where c.source_id =
> p.crawled_page_id);
>
> *
> QUERY PLAN
> ---------------------------------------------------------------------------------------
> HashAggregate (cost=1516749.47..1520576.06 rows=382659 width=8)
> -> Hash Anti Join (cost=1294152.41..1515791.80 rows=383071 width=8)
> Hash Cond: (p.crawled_page_id = c.source_id)
> -> Seq Scan on page_content p (cost=0.00..87132.17
> rows=428817 width=8)
> -> Hash (cost=771182.96..771182.96 rows=31876196 width=4)
> -> Seq Scan on clause2 c (cost=0.00..771182.96
> rows=31876196 width=4)
> (6 rows)
>
> And my explain analyze output is :
>
> QUERY PLAN
> --------------------------------------------------------------------------------------------------------------------------------------------
> HashAggregate (cost=1516749.47..1520576.06 rows=382659 width=8)
> (actual time=56666.181..56669.270 rows=72 loops=1)
> -> Hash Anti Join (cost=1294152.41..1515791.80 rows=383071
> width=8) (actual time=45740.789..56665.816 rows=74 loops=1)
> Hash Cond: (p.crawled_page_id = c.source_id)
> -> Seq Scan on page_content p (cost=0.00..87132.17
> rows=428817 width=8) (actual time=0.012..715.915 rows=428467 loops=1)
> -> Hash (cost=771182.96..771182.96 rows=31876196 width=4)
> (actual time=45310.524..45310.524 rows=31853083 loops=1)
> -> Seq Scan on clause2 c (cost=0.00..771182.96
> rows=31876196 width=4) (actual time=0.055..23408.884 rows=31853083
> loops=1)
> Total runtime: 56687.660 ms
> (7 rows)
>
> But Is there is any option to tune it further and one more thing
> output rows varies from 6 to 7.
You need an index on source_id to prevent seq scan, like the next:
CREATE INDEX idx_clause2_source_id
ON clause2
(source_id);*

*Best regards, Vitalii Tymchyshyn