I noticed that heap_tuple_needs_freeze might return true in cases where
the Xmax is leftover junk from somebody who set HEAP_XMAX_INVALID in the
far past without resetting the Xmax value itself to Invalid. I think
this is incorrect usage; the rule, I think, is that one shouldn't even
read Xmax at all unless HEAP_XMAX_INVALID is reset.
This might cause unnecessary acquisitions of the cleanup lock, if a
tuple is deemed freezable when in fact it isn't.
Suggested patch attached. I'd backpatch this as far as it applies
Álvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
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