Re: Multiple-Table-Spanning Joins with ORs in WHERE Clause

On 23.09.2016 11:00, Pavel Stehule wrote:
> 2016-09-23 8:35 GMT+02:00 Sven R. Kunze <srkunze(at)mail(dot)de
> <mailto:srkunze(at)mail(dot)de>>:
>
> I was wondering: would it be possible for PostgreSQL to rewrite
> the query to generate the UNION (or subquery plan if it's also
> fast) on it's own?
>
>
> It depends on real data. On your specific data the UNION variant is
> pretty fast, on different set, the UNION can be pretty slow. It is
> related to difficult OR predicate estimation.

I figure that the UNION is fast if the sub-results are small (which they
are in our case). On the contrary, when they are huge, the OUTER JOIN
variant might be preferable.

Is there something I can do to help here?

Or do you think it's naturally application-dependent and thus should be
solved with application logic just as we did?

Cheers,
Sven