Re: Preformance

On Sat, Feb 02, 2002 at 05:09:58PM -0500, Tom Lane wrote:
> Cees van de Griend <cees-list@griend.xs4all.nl> writes:
> > What can possible be the cause of the difference in preformance?
>
> Probably the VACUUM ANALYZE statistics changed just enough to push the
> planner into making the wrong choice.  You could experiment with doing
> "set enable_nestloop to off" and then EXPLAIN to see what the plan and
> cost are; I'll bet that the estimated cost of the hash plan is now
> just fractionally more than that of the nestloop.
>
> Of course, the *true* costs are very different, which is why I consider
> this a planner estimation failure.

I have dumped the table, droped the table and put the dump back into the
database. Now the speed is as it should be (for the time being).

If I understand you explanation, a possible hack to circumvent this problem
could be to trick the planner into thinking that it should use the hash
scan method, by inserting dummy data into the tbl[XXX]Number.

Another possible fix is to execute 'SET enable_nestloop = OFF;' before every
query.

Is this correct?

>             regards, tom lane

Regards,
Cees.