Re: ALTER TABLE ADD COLUMN fast default

Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com> writes:
> Attached is a patch for $subject. It's based on Serge Reilau's patch of
> about a year ago, taking into account comments made at the time. with
> bitrot removed and other enhancements such as documentation.

> Essentially it stores a value in pg_attribute that is used when the
> stored tuple is missing the attribute. This works unless the default
> expression is volatile, in which case a table rewrite is forced as
> happens now.

I'm quite disturbed both by the sheer invasiveness of this patch
(eg, changing the API of heap_attisnull()) and by the amount of logic
it adds to fundamental tuple-deconstruction code paths. I think
we'll need to ask some hard questions about whether the feature gained
is worth the distributed performance loss that will ensue.

regards, tom lane