SSI heap_insert and page-level predicate locks

heap_insert() calls CheckForSerializableConflictIn(), which checks if
there is a predicate lock on the whole relation, or on the page we're
inserting to. It does not check for tuple-level locks, because there
can't be any locks on a tuple that didn't exist before.

AFAICS, the check for page lock is actually unnecessary. A page-level
lock on a heap only occurs when tuple-level locks are promoted. It is
just a coarser-grain representation of holding locks on all tuples on
the page, *that exist already*. It is not a "gap" lock like the index
locks are, it doesn't need to conflict with inserting new tuples on the
page. In fact, if heap_insert chose to insert the tuple on some other
heap page, there would have been no conflict.

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Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com