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Xlle can't be generally avoided so we have to take conservatively first.

Why it cannot be avoided? What is it needed for?

The main purpose is to discern at recovery a prepared XA (XAP) that was never binlogged from one that was. Your case

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Another way to do this is to delay the binlog checkpoints until all XA PREPARE in a binlog file have been XA COMMIT'ted

assumes that XAC must always come in "normal" time. But of course, being a part of the user's decision, it can be late significantly up until a purge from binary logs that contain the incl the total RESET MASTER. In the latter case its eventual post RM XA-COMMIT would be bin-logged with the full awareness.