On 07/12/2011 10:04 PM, Tom Lane wrote:
Mario Splivalo<mario.spliv...@megafon.hr> writes:
Limit (cost=0.00..415.91 rows=21 width=8) (actual
time=11263.089..11263.089 rows=0 loops=1)
-> Nested Loop (cost=0.00..186249.55 rows=9404 width=8) (actual
time=11263.087..11263.087 rows=0 loops=1)
Why is planner using NestedLoops,
Because it thinks the LIMIT will kick in and end the query when the join
is only 21/9404ths (ie, a fraction of a percent) complete. A NestLoop
results in saving a lot of work in that situation, whereas hash-and-sort
has to do the whole join despite the LIMIT.
What you need to look into is why the estimated join size is 9400 rows
when the actual join size is zero. Are both tables ANALYZEd? Are you
intentionally selecting rows that have no join partners?
Hi, Tom.
Yes, both tables have been ANALYZEd. What do you mean, intentilnaly
selecting rows taht have no join partners?
Mario
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