Tom Lane wrote:
Another issue is that it might not be possible to update a page for
lack of space. Are we prepared to assume that there will never be a
transformation we need to apply that makes the data bigger? In such a
situation an in-place update might be impossible, and that certainly
takes it outside the bounds of what ReadBuffer can be expected to manage.
Would a possible solution to this be that you could
1. Upgrade to the newest minor-version of the old release
(which has knowledge of the space requirements of the
new one).
2. Run some new maintenance command like "vacuum expand" or
"vacuum prepare_for_upgrade" or something that would split
any too-full pages, leaving only pages with enough space.
3. Only then shutdown the old server and start the
new major-version server.
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