Group Replication System Variables Unit transactions The value of this system variable can be changed while Group Replication is running, but the change only takes effect after you stop and restart Group Replication on the group member. group_replication_clone_threshold  specifies the transaction gap, as a number of transactions, between the existing member (donor) and the joining member (recipient) that triggers the use of a remote cloning operation for state transfer to the joining member during the distributed recovery process. If the transaction gap between the joining member and a suitable donor exceeds the threshold, Group Replication begins distributed recovery with a remote cloning operation. If the transaction gap is below the threshold, or if the remote cloning operation is not technically possible, Group Replication proceeds directly to state transfer from a donor’s binary log. Warning Do not use a low setting for  group_replication_clone_threshold  in an active group. If a number of transactions above the threshold takes place in the group while the remote cloning operation is in progress, the joining member triggers a remote cloning operation again after restarting, and could continue this indefinitely. To avoid this situation, ensure that you set the threshold to a number higher than the number of transactions that you would expect to occur in the group during the time taken for the remote cloning operation. To use this function, both the donor and the joining member must be set up beforehand to support cloning. For instructions, see Section 18.5.3.2, “Cloning for Distributed Recovery” . When a remote cloning operation is carried out, Group Replication manages it for you, including the required server restart, provided that  group_replication_start_on_boot=ON  is set. If not, you must restart the server manually. The remote cloning operation replaces the existing data dictionary on the joining member, but Group Replication checks and does not proceed if the joining member has additional transactions that are not present on the other group members, because these transactions would be erased by the cloning operation. The default setting (which is the maximum permitted sequence number for a transaction in a GTID) means that state transfer from a donor’s binary log is virtually always attempted rather than cloning. However, note that Group Replication always attempts to execute a cloning operation, regardless of your threshold, if state transfer from a donor’s binary log is impossible, for example because the transactions needed by the joining member are not available in the binary logs on any existing group member. If you do not want to use cloning at all in your replication group, do not install the clone plugin on the members. • group_replication_communication_debug_options 3800 Command-Line Format --group-replication-communication- debug-options=value System Variable group_replication_communication_debug_options Scope Global Dynamic Yes SET_VAR  Hint Applies No Type String Default Value GCS_DEBUG_NONE Valid Values GCS_DEBUG_NONE GCS_DEBUG_BASIC