Re: How to change query planner configuration paramerters

Hi Raghavendra,

Thanks for your quick reply,
I did as you suggessted and following is my output.

melaka=# set enable_mergejoin to off;
SET
melaka=# show enable_mergejoin;
enable_mergejoin
------------------
off
(1 row)

Then I executed the following query
melaka=# EXPLAIN select * from distributors full outer join films on
distributors.did=films.did;

Then the output was
Merge Full Join (cost=10000000074.40..10000000093.69 rows=1159 width=286)
Merge Cond: (films.did = distributors.did)
-> Sort (cost=30.08..31.03 rows=380 width=184)
Sort Key: films.did
-> Seq Scan on films (cost=0.00..13.80 rows=380 width=184)
-> Sort (cost=44.32..45.85 rows=610 width=102)
Sort Key: distributors.did
-> Seq Scan on distributors (cost=0.00..16.10 rows=610 width=102)
(8 rows)

Can you suggest why the merge join is being suggested when I have turned it
off ?

On Sun, Sep 18, 2011 at 3:05 PM, Raghavendra <
raghavendra(dot)rao(at)enterprisedb(dot)com> wrote:

> postgres=# set enable_hashjoin to off;
> SET
> postgres=# show enable_hashjoin;
> enable_hashjoin
> -----------------
> off
> (1 row)
>
> Above, changes applies for the current session (its Session-Level). If you
> want to do at Database-level use ALTER DATABASE and for entire Cluster-level
> edit postgresql.conf and do changes as per your requirement.
>
> ---
> Regards,
> Raghavendra
> EnterpriseDB Corporation
> Blog: http://raghavt.blogspot.com/
>
>
>
> On Sun, Sep 18, 2011 at 2:55 PM, Melaka Gunasekara <donmelaka(at)gmail(dot)com>wrote:
>
>> Hi all,
>>
>> I came across
>> http://www.postgresql.org/docs/8.4/static/runtime-config-query.html which
>> describes
>> how to change query planner configuration paramerters.
>>
>> I need to know how I can change these parameters.
>> For example if I need to turn off enable_hashjoin, how can I do that?
>>
>> Best Regards,
>> Melaka
>>
>>
>

--
Best Regards,
Melaka