Re: Reduce lock levels for ADD and DROP COLUMN

Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Dec 27, 2010 at 6:42 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>> Idea is to reduce lock level of ADD/DROP COLUMN from AccessExclusiveLock
>> down to ShareRowExclusiveLock.
>> 
>> To make it work, we need to recognise that we are adding a column
>> without rewriting the table.

> Can you elaborate on why you think that's the right test?  It seems to
> me there could be code out there that assumes that the tuple
> descriptor won't change under it while it holds an AccessShareLock.

s/could/definitely is/

I think this is guaranteed to break stuff; to the point that I'm
not even going to review the proposal in any detail.
        regards, tom lane