Hi Greg,
First off, thanks for your reply.
I had actually just read your blog before writing this.
I should have been more clear in my first post.
If you use ALTER TABLE it will check every row in the table to make sure the column doesn't exceed the constraint (in 8.4 - I know this has been updated in 9.x)
As I am trying to update a table with hundreds of millions of rows and the only way to do this efficiently (in an online database with 4 9's availability) is with a pg_attribute update. Previously we have done this via a script that runs for about a week on the database to migrate to another column, but this also involves code changes and lots and lots of testing.
So my question is - does postgres take an update to pg_attribute instantly and in a reliable manner?
thanks,
Justin.