Re: Allowing ALTER TYPE to change storage strategy

On Fri, Feb 28, 2020 at 08:35:33PM -0500, Tom Lane wrote:
>Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
>> I think we might check if there are any attributes with the given data
>> type, and allow the change if there are none. That would still allow the
>> change when the type is used only for things like function parameters
>> etc. But we'd also have to check for domains (recursively).
>
>Still has race conditions.
>

Yeah, I have no problem believing that.

>> One thing I haven't mentioned in the original message is CASCADE. It
>> seems useful to optionally change storage for all attributes with the
>> given data type. But I'm not sure it's actually a good idea, and the
>> amount of code seems non-trivial (it'd have to copy quite a bit of code
>> from ALTER TABLE).
>
>You'd need a moderately strong lock on each such table, which means
>there'd be serious deadlock hazards. I'm dubious that it's worth
>troubling with.
>

Yeah, I don't plan to do this in v1 (and I have no immediate plan to
work on it after that). But I wonder how is the deadlock risk any
different compared e.g. to DROP TYPE ... CASCADE?

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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