Re: enabling nestedloop and disabling hashjon

I am sorry for the late reply, when I disabled the hash join command
"enable_hashjoin=off" in the postgresql.conf file, it was not working. But
I when I used the command "set enable_hashjoin=off" command in the back
end. It worked.
I am not able to understand why it did not get disabled when I changed it
in the postgresql file.
ᐧ

On Fri, Feb 13, 2015 at 2:34 AM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> wrote:

> On 2/10/15 9:29 AM, Tom Lane wrote:
>
>> Ravi Kiran <ravi(dot)kolanpaka(at)gmail(dot)com> writes:
>>
>>> yes sir, I did try the pg_ctl reload command, but its still using the
>>> hash
>>> join algorithm and not the nested loop algorithm. I even restarted the
>>> server, even then its still using the hash join algorithm
>>>
>>
>> Does "show enable_hashjoin" say it's off? If not, I think you must've
>> fat-fingered the postgresql.conf change somehow.
>>
>
> For future reference, posts like this belong on pgsql-performance.
>
> The other possibility is that the query estimates are so high that the
> setting doesn't matter. When you set any of the enable_* settings to off,
> all that really happens is the planner adds a cost of 10M to those nodes
> when it's planning. Normally that's enough to toss those plans out, but in
> extreme cases the cost estimates will still come up with the un-desired
> plan.
>
> Can you post EXPLAIN ANALYZE output with the setting on and off? Or at
> least plain EXLPAIN output.
> --
> Jim Nasby, Data Architect, Blue Treble Consulting
> Data in Trouble? Get it in Treble! http://BlueTreble.com
>