From: | daveg <daveg(at)sonic(dot)net> |
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To: | Robert Treat <xzilla(at)users(dot)sourceforge(dot)net> |
Cc: | pgsql-hackers(at)postgresql(dot)org, Simon Riggs <simon(at)2ndquadrant(dot)com>, Hans-Jürgen Schönig <postgres(at)cybertec(dot)at>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net> |
Subject: | Re: Mini improvement: statement_cost_limit |
Date: | 2008-08-05 01:01:02 |
Message-ID: | 20080805010102.GR4818@sonic.net |
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Lists: | pgsql-hackers |
On Mon, Aug 04, 2008 at 05:19:50PM -0400, Robert Treat wrote:
> See, this is what we ended up talking about before. Someone will say "I'd like
> to prevent my devs from accidentally doing queries with cartesian products"
> and they will use this to do it... but that will only work in some cases, so
> it becomes a poor tool to solve a different problem.
>
> BTW, what I really love about statement costs, is that they aren't even
> reliable on the same machine with the same data. I have seen query plans
> which run on the same data on the same machine where the resultant query
> runtime can vary from 2 hours to 5 hours, depending on how much other
> concurrent traffic is on the machine. Awesome eh?
Sure, I don't think anyone believes that costs are precise. But the case that
is interesting is 2 hours versus years and years.
> The footgun in my mind is that people will think this solves a number of
> problems even though it doesnt solve them well. However, the footgun for yo
I suspect that a good solution to this problem is impossible as it is more
or less the halting problem. So I'm willing to accept a poor solution based
on costs and then hope we improve the cost model.
-dg
--
David Gould daveg(at)sonic(dot)net 510 536 1443 510 282 0869
If simplicity worked, the world would be overrun with insects.
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