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group_replication_tls_source  specifies the source of TLS material for Group Replication. 

• group_replication_transaction_size_limit 

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This system variable should have the same value on all group members. The value of this system variable can be changed while Group Replication is running. The change takes effect immediately on the group member, and applies from the next transaction started on that member. During this process, the value of the system variable is permitted to differ between group members, but some transactions might be rejected. 

group_replication_transaction_size_limit  configures the maximum transaction size in bytes which the replication group accepts. Transactions larger than this size are rolled back by the receiving member and are not broadcast to the group. Large transactions can cause problems for a replication group in terms of memory allocation, which can cause the system to slow down, or in terms of network bandwidth consumption, which can cause a member to be suspected of having failed because it is busy processing the large transaction. 

When this system variable is set to 0 there is no limit to the size of transactions the group accepts. From MySQL 8.0, the default setting for this system variable is 150000000 bytes (approximately 143 MB). Adjust the value of this system variable depending on the maximum message size that you need the group to tolerate, bearing in mind that the time taken to process a transaction is proportional to its size. The value of group_replication_transaction_size_limit  should be the same on all group members. For further mitigation strategies for large transactions, see Section 18.3.2, “Group Replication Limitations” . 

• group_replication_unreachable_majority_timeout 

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