Re: same query in high number of times - Mailing list pgsql-performance

duration: 2533.734 ms  statement:

SELECT news.url_text,news.title, comments.name, comments.createdate, comments.user_id, comments.comment FROM news, comments WHERE comments.cid=news.id  AND comments.published='1' GROUP BY news.url_text,news.title comments.name, comments.createdate, comments.user_id, comments.comment ORDER BY comments.createdate DESC LIMIT 3


And here is the query plan :
                                                              QUERY PLAN                                                              
----------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=4313.54..4313.55 rows=3 width=595) (actual time=288.525..288.528 rows=3 loops=1)
   ->  Sort  (cost=4313.54..4347.26 rows=13486 width=595) (actual time=288.523..288.523 rows=3 loops=1)
         Sort Key: comments.createdate
         ->  HashAggregate  (cost=3253.60..3388.46 rows=13486 width=595) (actual time=137.521..148.132 rows=13415 loops=1)
               ->  Hash Join  (cost=1400.73..3051.31 rows=13486 width=595) (actual time=14.298..51.049 rows=13578 loops=1)
                     Hash Cond: ("outer".cid = "inner".id)
                     ->  Seq Scan on comments  (cost=0.00..1178.72 rows=13480 width=522) (actual time=0.012..17.434 rows=13418 loops=1)
                           Filter: (published = 1)
                     ->  Hash  (cost=1391.18..1391.18 rows=3818 width=81) (actual time=14.268..14.268 rows=3818 loops=1)
                           ->  Seq Scan on news  (cost=0.00..1391.18 rows=3818 width=81) (actual time=0.021..10.072 rows=3818 loops=1)

The same is being requested from different sessions . So why is it not being cached .

work_mem = 51024                        # min 64, size in KB