|From:||Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>|
|To:||Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>|
|Subject:||Re: ALTER TABLE ADD COLUMN fast default|
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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
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