From: Scott Marlowe <scott.marlowe@gmail.com>
To: Justin <justin@emproshunts.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: getting estimated cost to agree with actual
Date: Mon, 2 Jun 2008 17:38:21 -0600
Message-ID: <dcc563d10806021638t6619ef6cw67f2606541cd90f6@mail.gmail.com> (raw)
In-Reply-To: <4844696D.20307@emproshunts.com>
References: <4844696D.20307@emproshunts.com>
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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To: pgsql-performance@postgresql.org
Cc: scott.marlowe@gmail.com, justin@emproshunts.com
Subject: Re: getting estimated cost to agree with actual
In-Reply-To: <dcc563d10806021638t6619ef6cw67f2606541cd90f6@mail.gmail.com>
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