Re: BUG #15102: Performance problem when doing join, index are not used

Hello,

Thanks a lot for your answer. I did change parameters and will retry the
query.

I am sorry for posting in the bad list and will put any future performance
questions at pgsql-performance.

Have a nice day,
Mehdi Rahman

2018-03-08 16:41 GMT+01:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> =?utf-8?q?PG_Bug_reporting_form?= <noreply(at)postgresql(dot)org> writes:
> > Here is the query:
> > [ select with 11 input tables ]
>
> Perhaps raising join_collapse_limit to 11 or more would let the query
> planner find a better plan. Having said that, I see no especially good
> reason to think that sort-and-merge isn't a good join type for this query.
> Indexes aren't always the answer, especially not when joining large
> numbers of rows as you are here.
>
> Another direction to pursue is to raise work_mem to allow the sorts to
> proceed more efficiently. Don't go overboard on that, but judicious
> increases can help.
>
> Lastly, I see no reason whatever to think this is a bug. You might
> have better luck discussing the issue on the pgsql-performance list.
>
> regards, tom lane
>