•You do not need to set up a list of valid donors in the clone_valid_donor_list  system variable for the purpose of joining a replication group. Group Replication configures this setting automatically for you after it selects a donor from the existing group members. Note that remote cloning operations use the server’s SQL protocol hostname and port. 

•The clone plugin has a number of system variables to manage the network load and performance impact of the remote cloning operation. Group Replication does not configure these settings, so you can review them and set them if you want to, or allow them to default. Note that when a remote cloning operation is used for distributed recovery, the clone plugin’s clone_enable_compression  setting applies to the operation, rather than the Group Replication compression setting. 

•To invoke the remote cloning operation on the recipient, Group Replication uses the internal mysql.session  user, which already has the CLONE_ADMIN  privilege, so you do not need to set this up. 

•As the clone user on the donor for the remote cloning operation, Group Replication uses the replication user that you set up for distributed recovery (which is covered in Section 18.2.1.3, “User Credentials For Distributed Recovery” ). You must therefore give the BACKUP_ADMIN  privilege to this replication user on all group members that support cloning. Also give the privilege to the replication user on joining members when you are configuring them for Group Replication, because they can act as donors after they join the group. The same replication user is used for distributed recovery on every group member. To give this privilege to the replication user on existing members, you can issue this statement on each group member individually with binary logging disabled, or on one group member with binary logging enabled: 

GRANT BACKUP_ADMIN ON *.* TO rpl_user @’%’; 

•If you use START GROUP_REPLICATION  to specify the replication user credentials on a server that previously supplied the user credentials using CHANGE REPLICATION SOURCE TO  | CHANGE MASTER TO , ensure that you remove the user credentials from the replication metadata repositories before any remote cloning operations take place. Also ensure that group_replication_start_on_boot=OFF is set on the joining member. For instructions, see Section 18.6.3, “Securing Distributed Recovery Connections” . If you do not unset the user credentials, they are transferred to the joining member during remote cloning operations. The group_replication_recovery  channel could then be inadvertently started with the stored credentials, on either the original member or members that were cloned from it. An automatic start of Group Replication on server boot (including after a remote cloning operation) would use the stored user credentials, and they would also be used if an operator did not specify the distributed recovery credentials on a START GROUP_REPLICATION  command. 

## Threshold for Cloning 

When group members have been set up to support cloning, the group_replication_clone_threshold  system variable specifies a threshold, expressed as a number of transactions, for the use of a remote cloning operation in distributed recovery. If the gap between the transactions on the donor and the transactions on the joining member is larger than this number, a remote cloning operation is used for state transfer to the joining member when this is technically possible. Group Replication calculates whether the threshold has been exceeded based on the gtid_executed  sets of the existing group members. Using a remote cloning operation in the event of a large transaction gap lets you add new members to the group without transferring the group’s data to the server manually beforehand, and also enables a member that is very out of date to catch up more efficiently. 

The default setting for the group_replication_clone_threshold  Group Replication system variable is extremely high (the maximum permitted sequence number for a transaction in a GTID), so it effectively deactivates cloning wherever state transfer from the binary log is possible. To enable Group Replication to 

