pageinspect option to forgo buffer locking?

Hi,

Occasionally, when debugging issues, I find it quite useful to be able
to do a heap_page_items() on a page that's actually locked exclusively
concurrently. E.g. investigating the recent multixact vacuuming issues,
it was very useful to attach a debugger to one backend to step through
freezing, and display the page in another session.

Currently the locking in get_raw_page_internal() prevents that. If it's
an option defaulting to off, I don't see why we couldn't allow that to
skip locking the page's contents. Obviously you can get corrupted
contents that way, but we already allow to pass arbitrary stuff to
heap_page_items(). Since pinning wouldn't be changed, there's no danger
of the page being moved out from under us.

Greetings,

Andres Freund