Is there a way to add a NOT NULL constraint to a column without having to lock the table while a sequential read happens? Seems like it should be possible to add an index on the column for null values, like: create index on t using btree(col_name) where col_name is null; Then when adding the not null constraint, pg could lock the table, use that index to see if there's any nulls, and if there's not, add the constraint. (That's not possible already, right? I couldn't figure it out if it was.) Right now, the strategy for adding a not null constraint to a column without any significant downtime involves creating a new table, as I understand it. Joe
