Re: What about utility to calculate planner cost constants?

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От
Ron Mayer
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Re: What about utility to calculate planner cost constants?
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4240A360.1030904@cheapcomplexdevices.com
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Re: What about utility to calculate planner cost constants? Christopher Browne <cbbrowne@acm.org>
Re: What about utility to calculate planner cost constants? Tom Lane <tgl@sss.pgh.pa.us>
Re: What about utility to calculate planner cost constants? Greg Stark <gsstark@mit.edu>
Re: What about utility to calculate planner cost constants? Tom Lane <tgl@sss.pgh.pa.us>
Re: What about utility to calculate planner cost constants? Ron Mayer <rm_pg@cheapcomplexdevices.com>
Re: What about utility to calculate planner cost constants? Kenneth Marshall <ktm@it.is.rice.edu>
Re: What about utility to calculate planner cost constants? Bruno Wolff III <bruno@wolff.to>
Re: What about utility to calculate planner cost constants? Greg Stark <gsstark@mit.edu>
Re: What about utility to calculate planner cost constants? Tom Lane <tgl@sss.pgh.pa.us>
Tom Lane wrote:
> 
> And you can't just dismiss the issue of wrong cost models and say we can
> get numbers anyway.

Is there a way to see more details about the cost estimates.
EXPLAIN ANALYZE seems to show the total time and rows; but not
information like how many disk pages were accessed.

I get the feeling that sometimes the number of rows is estimated
very well, but the amount of disk I/O is way off.

Sometimes the number of pages read/written is grossly
overestimated (if tables lave a lot of locally clustered data)
or underestimated if a sort barely exceeds sort_mem.


Perhaps an EXPLAN ANALYZE VERBOSE that would add info like this:

    Index scan ([...]estimated 1000 pages read)  (actual[...] 10 pages read)

would help track those down?

В списке pgsql-performance по дате отправления
От: Dave Held
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От: Ron Mayer
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Сообщение: Re: Planner issue
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