Saturday, December 30, 2006

Rebuilding large GIN indexes

Rebuilding large GIN indexes

takes time. A lot of time. With rebuilding, I mean when you for example have to UPDATE all your tsvector fields due to a change in tsearch2 configuration. (Yes, I had to do that because I had a slightly incorrect tsearch2 configuration for the archives search database). So don't do it. Instead use the fact that PostgreSQL has nice transactional DDL and do something like this:


CREATE TABLE messages_new AS SELECT id,txt,to_tsvector(txt) AS fti

FROM messages;

CREATE INDEX messages_new_fti ON messages_new USING gin(fti);

ANALYZE messags_new;

ALTER TABLE messages RENAME TO messages_old;

ALTER TABLE messages_new RENAME TO messages;


DROP TABLE messages_old;

ALTER INDEX messages_new_fti RENAME TO messages_fti;

(apologies for any typos, I didn't bother to actually type these commands into the database again, and I lost my cut-and-paste of what I ran)

This way, the messages table can still serve up searches without any disruption to the searches at all. And creating the new index is a lot faster than updating the existing one if you have to touch all rows.

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