| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | Neto pr <netoprbr9(at)gmail(dot)com> |
| Cc: | vjain(at)opentable(dot)com, johnescm(at)hotmail(dot)com, PostgreSQL General <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: [External] RE: Estimate time without running the query |
| Date: | 2018-09-13 22:53:15 |
| Message-ID: | CAKFQuwYsH5qU+fB6dQP_d7QXhZ7jvnkE3qrJmir+nicj9U_mVg@mail.gmail.com |
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| Lists: | pgsql-general |
On Thu, Sep 13, 2018 at 3:30 PM, Neto pr <netoprbr9(at)gmail(dot)com> wrote:
> The problem is that using the explain analyze <query> I have to wait for
> the query to execute.
> I would like to estimate the time without having to wait for the query
> execution.
> Does anyone know how to estimate the time without waiting for the query to
> be executed?
>
On the machine in question you have to experiment to obtain data to
construct a formula to convert cost to time. Then when using the function
remember that lots of things can play into individual executions taking
more time (and sometimes less too I suspect) such as locks, caching,
physical data locality.
It seems more useful to log actual execution times and look for trends. If
you are writing a query odds are it needs to be run regardless of how
efficient it may be - or used in a relative comparison to an alternate
query.
David J.
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