Re: Cost limit.

On Fri, 18 May 2001, Tom Lane wrote:

> Given the inherent inaccuracy of the cost estimates, I'd be real
> hesitant to rely on them to suppress overly-expensive queries.

That's just it.  You don't have to be that accurate.  If an estimate
goes into the millions or billions, something is obviously wrong with
the query, period.  I'd just like to set a cutoff.

> What might make sense is a time limit on execution (after x amount
> of time, give up and cancel the query).

That would work, but during that time the query is executing, that
process is eating up cpu power and stealing resources from valid
queries, possibly making them run slower, thus causing a chain of
queries that could eventually time out as well.

> Note you could implement such a time limit purely on the client side,
> which might be an easier and more flexible way to go.

That's just it.  PHP (our front end) has a 30 second time limit we
have not overridden.  But we've found that after the PHP execution stops
in disgust, the postgres thread keeps going until we restart the
postgres back end.  That is simply unacceptable.  Especially
considering any user on our system could feasibly (accidently or
maliciously) take our database server to a crawl by writing a
single bad query that may take days to track down.

--
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| Shaun M. Thomas                INN Database Programmer              |
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