Previously AELs were registered against the top-level xid, which could
cause locks to be held much longer than necessary in some cases during
Hot Standby replay. We now record locks directly against their appropriate
xids. Requires few code changes because original code allowed for this
situation but didn’t fully implement it.

Discussion: CAKJS1f9vJ841HY=wonnLVbfkTWGYWdPN72VMxnArcGCjF3SywA@mail.gmail.com

Author: Simon Riggs and David Rowley