Re: UPDATE 6m records quickly

[James Day]

You might try to do the updates in chunks which match the physical order of the records (order added for MyISAM unless you've done an ALTER TABLE .. ORDER BY, primary key for InnoDB). Working in chunks by physical order the select will get the data quickly with few sequential reads and the update will update it while it's still cached from the select. Otherwise you'd need to hold all the affected records in cache and that can be a challenge compared to a chunk size you can choose so that it always fits.