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group_replication_message_cache_size  applies only to the data stored in the cache, and the cache structures require an additional 50 MB of memory. 

The cache size limit can be increased or reduced dynamically at runtime. If you reduce the cache size limit, XCom removes the oldest entries that have been decided and delivered until the current size is below the limit. Group Replication’s Group Communication System (GCS) alerts you, by a warning message, when a message that is likely to be needed for recovery by a member that is currently unreachable is removed from the message cache. For more information on tuning the message cache size, see Section 18.7.5, “XCom Cache Management” . 

• group_replication_poll_spin_loops 

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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_poll_spin_loops  specifies the number of times the group communication thread waits for the communication engine mutex to be released before the thread waits for more incoming network messages. 

• group_replication_recovery_complete_at 

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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_recovery_complete_at  specifies the policy applied during the distributed recovery process when handling cached transactions after state transfer from an existing member. You 

