Re: ALTER TABLE DROP COLUMN

The Hermit Hacker <scrappy(at)hub(dot)org> writes:
> hrmm .. mvcc uses a timestamp, no? is there no way of using that
> timestamp to determine which columns have/haven't been cleaned up
> following a crash? maybe some way of marking a table as being in a 'drop
> column' mode, so that when it gets brought back up again, it is scan'd for
> any tuples older then that date?

WAL would provide the framework to do something like that, but I still
say it'd be a bad idea. What you're describing is
irrevocable-once-it-starts DROP COLUMN; there is no way to roll it back.
We're trying to get rid of statements that act that way, not add more.

I am not convinced that a 2x penalty for DROP COLUMN is such a huge
problem that we should give up all the normal safety features of SQL
in order to avoid it. Seems to me that DROP COLUMN is only a big issue
during DB development, when you're usually working with relatively small
amounts of test data anyway.

regards, tom lane