Certainly we need to upgrade to an exclusive table lock to replace the heap table.
Well, we will be holding an ExclusiveLock on the heap relation regardless. We "replace" the heap table by swapping its relfilenode, so ISTM we needn't hold an AccessExclusiveLock.
Do we want to get a shared lock and possibly starve waiting for an exclusive lock on the table to swap the new one in?
What I'm saying is that REINDEX on non-shared indexes need only acquire an ExclusiveLock, and hence not need to escalate its lock.
-Neil
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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
