Re: statement_cost_limit

On Wed, 2006-03-01 at 11:47 -0500, Tom Lane wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> > A new parameter that allows the administrator to place sensible limits
> > on the size of queries executed.
>
> As I said when the idea was floated originally, I don't think this is a
> very good idea at all. The planner's estimates are sufficiently often
> wrong that refusing to execute queries on the strength of an estimated
> cost is going to burn you in both directions.

That depends upon your view on risk. Some admins would rather abort a
few queries wrongly in less than a second than risk having a query run
for hours before being cancelled by statement_timeout. Most end-users
would agree with this, because if the answer is No they want to hear it
quickly so they can correct their mistake and continue.

But I think the estimates aren't sufficiently wrong to make a big
difference. People with a 100GB+ table can set it with sufficiently
useful accuracy to avoid pointless attempts to sort that table, for
example.

> Even if it were a good idea, the proposed location of the test is 100%
> wrong, as you are only guarding one path of query submission. Or were
> you intending that the restriction be trivial to subvert?

The main idea was to guard the path by which ad-hoc queries would come,
but you might want to set it on a dev server also for example.

Its a discussion point as to whether we'd want it the way I've coded, or
whether you want to block other routes also. I can see things both ways
on that and have no problem changing the behaviour if that is the
consensus; that change would be fairly quick.

Best Regards, Simon Riggs