| From: | AI Rumman <rummandba(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Kevin Grittner <kgrittn(at)mail(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Evgeny Shishkin <itparanoia(at)gmail(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, postgres performance list <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Why does the number of rows are different in actual and estimated. |
| Date: | 2012-12-14 19:28:50 |
| Message-ID: | CAGoODpdQsOE7fwT47SOhSq7QcQcfEKSPHANf7Yu_GjJYRVT-hA@mail.gmail.com |
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| Lists: | pgsql-performance |
So I am going to change
join_collapse_limit
and
from_collapse_limit
to 20.
Do I need to set geqo_threshold to greater than 20. Now it is 12 ( default).
And could you let me know why geqo_optimizer is not working good in this
case?
On Fri, Dec 14, 2012 at 2:22 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Kevin Grittner" <kgrittn(at)mail(dot)com> writes:
> > AI Rumman wrote:
> >> Does FK Constraint help to improve performance? Or it is only
> >> for maintaining data integrity?
>
> > I'm not aware of any situation where adding a foreign key
> > constraint would improve performance.
>
> There's been talk of teaching the planner to use the existence of FK
> constraints to improve plans, but I don't believe any such thing is
> in the code today.
>
> regards, tom lane
>
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