From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Lakhin <exclusion@gmail.com>
cc: pgsql-bugs@lists.postgresql.org,
        Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Subject: Re: BUG #17872: Dropping an attribute of a composite type breaks
 indexes over the type silently
In-reply-to: <1aa2eec0-2017-3870-6d88-228d08c587d3@gmail.com>
References: <17872-d0fbb799dc3fd85d@postgresql.org>
 <3169550.1679928579@sss.pgh.pa.us> <3182314.1679935605@sss.pgh.pa.us>
 <1aa2eec0-2017-3870-6d88-228d08c587d3@gmail.com>
Comments: In-reply-to Alexander Lakhin <exclusion@gmail.com>
	message dated "Mon, 27 Mar 2023 21:00:00 +0300"
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Date: Mon, 27 Mar 2023 14:20:13 -0400
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Alexander Lakhin <exclusion@gmail.com> writes:
> Yes, I think something like that can resolve the issue.
> But I would also note that the problem is not with indexes only, but also
> with "... partition by list(comp_type_value)", for example.

Hmm ... really?  I'd just concluded that a partitioned table is okay
as long as it doesn't yet have any partitions.  Even if the modified
type is a partitioning column, there's no structure yet that could
depend on the contents of the type.  (If it does have partitions,
we'll fail when we get to one of those.)

[ thinks some more... ] I guess there's the corner case where we
replace, say, a hashable type with a non-hashable one and thereby
break decisions about whether PARTITION BY HASH is allowable.
That's kind of a stretch.  But find_composite_type_dependencies
currently rejects partitioned tables, so we're not taking away any
functionality if we continue to forbid that.

			regards, tom lane