planner's midjudge number of rows resulting, despite pretty obvious join
- From: Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>
- To: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
- Subject: planner's midjudge number of rows resulting, despite pretty obvious join
- Date: Tue, 24 Feb 2009 14:33:55 +0000
- Message-id: <2f4958ff0902240633y46e9ed96s3bc73434f75d269f@mail.gmail.com> <text/plain>
explain select ss, ARRAY(select id from foo where ss>0 and id between
7 and 156 order by random() limit 3) as v from
generate_series(1,1000000) ss;
QUERY PLAN
------------------------------------------------------------------------------------
Function Scan on generate_series ss (cost=0.00..9381.22 rows=1000 width=4)
SubPlan
-> Limit (cost=9.36..9.37 rows=3 width=8)
-> Sort (cost=9.36..9.74 rows=150 width=8)
Sort Key: (random())
-> Result (cost=0.00..7.42 rows=150 width=8)
One-Time Filter: ($0 > 0)
-> Seq Scan on foo (cost=0.00..7.05 rows=150 width=8)
Filter: ((id >= 7) AND (id <= 156))
(9 rows)
:(
no matter if I change last generate_series's range, it will always
estimate 1000 rows...
--
GJ
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