Re: Query taking too long. Problem reading explain output.

Henrik wrote:

> Ahh I had exactly 8 joins.
> Following your suggestion I raised the join_collapse_limit from 8 to 10 and
> the planners decision sure changed but now I have some crazy nested loops.
> Maybe I have some statistics wrong?

Yeah. The problematic misestimation is exactly the innermost indexscan,
which is wrong by two orders of magnitude:

> -> Index Scan using
> tbl_file_idx on tbl_file (cost=0.01..8.66 rows=1 width=39) (actual
> time=0.057..931.546 rows=2223 loops=1)
> Index Cond:
> ((lower((file_name)::text) ~>=~ 'index.php'::character varying) AND
> (lower((file_name)::text) ~<~ 'index.phq'::character varying))
> Filter:
> (lower((file_name)::text) ~~ 'index.php%'::text)

This wreaks havoc on the rest of the plan. If this weren't
misestimated, it wouldn't be using those nested loops.

--
Alvaro Herrera http://www.CommandPrompt.com/
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