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DecommissionJob is also a type of AlterJob. When AlterJobV2 was introduced before, DecommissionJob was not modified accordingly. In fact, the Decommission operation does not need to generate a Job, but only need to mark the corresponding Backend state as Decommission. After that, the tablet repair logic will try to migrate the tablet on that Backend. And SystemHandler only needs to check all nodes marked as decommission, and then drop the emptied nodes.