Re: ALTER TABLE ADD COLUMN fast default

On 4/4/21 6:50 PM, Tom Lane wrote:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>> On 4/4/21 12:05 PM, Tom Lane wrote:
>>> I made CheckConstraintFetch likewise not install its array until
>>> it's done. I notice that it is throwing elog(ERROR) not WARNING
>>> for the equivalent cases of not finding the right number of
>>> entries. I wonder if we ought to back that off to a WARNING too.
>>> elog(ERROR) during relcache entry load is kinda nasty, because
>>> it prevents essentially *all* use of the relation. On the other
>>> hand, failing to enforce check constraints isn't lovely either.
>>> Anybody have opinions about that?
>> None of this is supposed to happen, is it? If you can't fetch the
>> constraints (and I think of a default as almost a kind of constraint)
>> your database is already somehow corrupted. So maybe if any of these
>> things happen we should ERROR out. Anything else seems likely to corrupt
>> the database further.
> Meh. "pg_class.relchecks is inconsistent with the number of entries
> in pg_constraint" does not seem to me like a scary enough situation
> to justify a panic response. Maybe there's an argument for failing
> at the point where we'd need to actually apply the CHECK constraints
> (similarly to what my patch is doing for missing defaults).
> But preventing the user from, say, dumping the data in the table
> seems to me to be making the situation worse not better.
>
>

OK, fair argument.

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com