Slow simple update query on PostgreSQL database with 3 million rows

Question

I am trying a simple UPDATE table SET column1 = 0 on a table with about 3 million rows on Postegres 8.4 but it is taking forever to finish. It has been running for more than 10 min.

Before, I tried to run a VACUUM and ANALYZE commands on that table and I also tried to create some indexes (although I doubt this will make any difference in this case) but none seems to help.

Any other ideas?

Update:

This is the table structure:

CREATE TABLE myTable
(
  id bigserial NOT NULL,
  title text,
  description text,
  link text,
  "type" character varying(255),
  generalFreq real,
  generalWeight real,
  author_id bigint,
  status_id bigint,
  CONSTRAINT resources_pkey PRIMARY KEY (id),
  CONSTRAINT author_pkey FOREIGN KEY (author_id)
      REFERENCES users (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT c_unique_status_id UNIQUE (status_id)
);

I am trying to run UPDATE myTable SET generalFreq = 0;

Answer 1

Take a look at this answer: PostgreSQL slow on a large table with arrays and lots of updates

First start with a better FILLFACTOR, do a VACUUM FULL to force table rewrite and check the HOT-updates after your UPDATE-query:

SELECT n_tup_hot_upd, * FROM pg_stat_user_tables WHERE relname = 'myTable';

HOT updates are much faster when you have a lot of records to update. More information about HOT can be found in this article.

Ps. You need version 8.3 or better.