Thread: using explain to get query expected time

using explain to get query expected time

From
Scara Maccai
Date:
Hi,

is there any chance to get the "Planner Cost Constants" right enough to get a "good" estimate in seconds of how long a
queryis supposed to run? 
The "rowcount" estimates are always good (there is no skew data at all in the db, values are pretty much "plain"
distributed)






Re: using explain to get query expected time

From
Joshua Tolley
Date:
On Mon, May 25, 2009 at 12:10:21AM -0700, Scara Maccai wrote:
> is there any chance to get the "Planner Cost Constants" right enough to get a "good" estimate in seconds of how long
aquery is supposed to run? 
> The "rowcount" estimates are always good (there is no skew data at all in the db, values are pretty much "plain"
distributed)

The most straightforward way I can think of would be to make sure your planner
constants (seq_page_cost, etc.) reflect time in meaningful units, which would
be very hard, and probably wouldn't work for reasons I don't know. Anyway, the
quick answer is no, 'cause it's really hard.

- Josh / eggyknap

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