Re: getting estimated cost to agree with actual

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От Scott Marlowe
Тема Re: getting estimated cost to agree with actual
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Msg-id dcc563d10806021638t6619ef6cw67f2606541cd90f6@mail.gmail.com
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Ответ на getting estimated cost to agree with actual  (Justin <justin@emproshunts.com>)
Ответы Re: getting estimated cost to agree with actual  (Gregory Stark <stark@enterprisedb.com>)
Список pgsql-performance
On Mon, Jun 2, 2008 at 3:43 PM, Justin <justin@emproshunts.com> wrote:
> As i've been looking over the more complicated queries that i have written
> and gotten allot of help in redoing the quires from you all, thanks again.
>
> I have noticed that  estimated Cost to do the query is way off from Actual.
>  The queries  don't run slow at least not to me. The Estimated Cost is way
> higher than the actual time on Hash joins but on the scan through the tables
> the Estimate Cost to  Actual flips where Actual is way higher than Estimated
> Cost
>
> I have tried increasing and decreasing the Stats on the important columns
> with no changes

Well, they're not measured in the same units.  estimated costs are in
terms of the cost to sequentially scan a single tuple, while actual
costs are in milliseconds.

You might be able to change the cost of sequential scan from 1 to
something else and everything else to reflect that change to get them
close.  But they aren't supposed to match directly up.

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