From: Dirk Lutzebäck <lutzeb@aeccom.com>
To: pgsql-performance@postgresql.org
Subject: Optimizer seems to be way off, why?
Date: Wed, 20 Jul 2005 17:25:09 +0200
Message-ID: <42DE6CD5.8070100@aeccom.com> (raw)
Hi,
I do not under stand the following explain output (pgsql 8.0.3):
explain analyze
select b.e from b, d
where b.r=516081780 and b.c=513652057 and b.e=d.e;
QUERY PLAN
----------------------------------------------------------------------------------------------------------------
Nested Loop (cost=0.00..1220.09 rows=1 width=4) (actual
time=0.213..2926.845 rows=324503 loops=1)
-> Index Scan using b_index on b (cost=0.00..1199.12 rows=1
width=4) (actual time=0.104..17.418 rows=3293 loops=1)
Index Cond: (r = 516081780::oid)
Filter: (c = 513652057::oid)
-> Index Scan using d_e_index on d (cost=0.00..19.22 rows=140
width=4) (actual time=0.009..0.380 rows=99 loops=3293)
Index Cond: ("outer".e = d.e)
Total runtime: 3638.783 ms
(7 rows)
Why is the rows estimate for b_index and the nested loop 1? It is
actually 3293 and 324503.
I did VACUUM ANALYZE before and I also increased the STATISTICS TARGET
on b.e to 500. No change.
Here is the size of the tables:
select count(oid) from b;
3532161
select count(oid) from b where r=516081780 and c=513652057;
3293
select count(oid) from d;
117270
Regards,
Dirk
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Subject: Re: Optimizer seems to be way off, why?
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