Re: Mini improvement: statement_cost_limit

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@sonic.net      510 536 1443    510 282 0869
If simplicity worked, the world would be overrun with insects.