Re: Suggestions on an update query

I forgot to include an additional parameter I am using in
Postgresql.conf:

checkpoint_segments = 30

Thanks,

Lance Campbell

Project Manager/Software Architect

Web Services at Public Affairs

University of Illinois

217.333.0382

http://webservices.uiuc.edu

________________________________

From: pgsql-performance-owner(at)postgresql(dot)org
[mailto:pgsql-performance-owner(at)postgresql(dot)org] On Behalf Of Campbell,
Lance
Sent: Friday, October 26, 2007 3:27 PM
To: pgsql-performance(at)postgresql(dot)org
Subject: [PERFORM] Suggestions on an update query

PostgreSql version 8.2.4

Memory = 8 Gig

CPUs 1 dual core Zeon running at 3.0

I have a problem with an update query taking over 10 hours in order to
run. I rebooted my server. I ran the SQL command "analyze". Could
you please help me with any suggestions? I have included the two tables
involved in the update below as well as the indexes I am using.

The table result_entry contains 17,767,240 rows and the table
question_number contains 40,787. Each row from the result_entry table
will match to one and only one row in the table question_number using
the fk_question_id field. Each row from the question_number table
matches to an average of 436 rows on the result_entry table.

CREATE TABLE question_number

(

fk_form_id integer not null,

fk_question_id integer not null,

question_number integer not null,

sequence_id integer not null

);

ALTER TABLE ONLY question_number ADD CONSTRAINT question_number_pkey
PRIMARY KEY (fk_question_id);

CREATE INDEX question_number_index1 ON question_number USING btree
(question_number);

CREATE TABLE result_entry (

fk_result_submission_id integer NOT NULL,

fk_question_id integer NOT NULL,

fk_option_order_id integer NOT NULL,

value character varying,

order_id integer NOT NULL,

question_number integer

);

CREATE INDEX result_entery_index1 ON result_entry USING btree
(fk_question_id);

update result_entry set question_number=question_number.question_number

from question_number where
result_entry.fk_question_id=question_number.fk_question_id;

explain update result_entry set
question_number=question_number.question_number

from question_number where
result_entry.fk_question_id=question_number.fk_question_id;

QUERY PLAN

------------------------------------------------------------------------
---------

Hash Join (cost=1437.71..1046983.94 rows=17333178 width=32)

Hash Cond: (result_entry.fk_question_id =
question_number.fk_question_id)

-> Seq Scan on result_entry (cost=0.00..612216.78 rows=17333178
width=28)

-> Hash (cost=927.87..927.87 rows=40787 width=8)

-> Seq Scan on question_number (cost=0.00..927.87 rows=40787
width=8)

(5 rows)

Postgresql.conf settings:

shared_buffers = 1GB

work_mem = 10MB

max_fsm_pages = 204800

random_page_cost = 1.0

effective_cache_size = 8GB

Thanks for any help!

Lance Campbell

Project Manager/Software Architect

Web Services at Public Affairs

University of Illinois

217.333.0382

http://webservices.uiuc.edu