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Re: TB-sized databases

From: david(at)lang(dot)hm
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Bill Moran <wmoran(at)collaborativefusion(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: TB-sized databases
Date: 2007-11-28 21:55:23
Message-ID: Pine.LNX.4.64.0711281352280.18750@asgard.lang.hm (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, 28 Nov 2007, Simon Riggs wrote:

> On Wed, 2007-11-28 at 14:48 +0100, Csaba Nagy wrote:
>
>> In fact an even more useful option would be to ask the planner to throw
>> error if the expected cost exceeds a certain threshold...
>
> Well, I've suggested it before:
>
> statement_cost_limit on pgsql-hackers, 1 March 2006
>
> Would people like me to re-write and resubmit this patch for 8.4?
>
> Tom's previous concerns were along the lines of "How would know what to
> set it to?", given that the planner costs are mostly arbitrary numbers.

arbitrary numbers are fine if they are relativly consistant with each 
other.

will a plan with a estimated cost of 1,000,000 take approximatly 100 times 
as long as one with a cost of 10,000?

or more importantly, will a plan with an estimated cost of 2000 reliably 
take longer then one with an estimated cost of 1000?

David Lang

> Any bright ideas, or is it we want it and we don't care about the
> possible difficulties?
>
>

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