Re: How to change query planner configuration paramerters

[Melaka Gunasekara <donmelaka@xxxxxxxxx>]

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.rao@xxxxxxxxxxxxxxxx> 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@xxxxxxxxx> 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