Message Compression group_replication_recovery_zstd_compression_level  system variables. For more information, see Section 4.2.8, “Connection Compression Control” . Binary log transaction compression (available as of MySQL 8.0.20), which is activated by the binlog_transaction_compression  system variable, can also be used to save bandwidth. The transaction payloads remain compressed when they are transferred between group members. If you use binary log transaction compression in combination with Group Replication’s message compression, message compression has less opportunity to act on the data, but can still compress headers and those events and transaction payloads that are uncompressed. For more information on binary log transaction compression, see Section 5.4.4.5, “Binary Log Transaction Compression” . Compression for messages sent in the group happens at the group communication engine level, before the data is handed over to the group communication thread, so it takes place within the context of the  mysql  user session thread. If the message payload size exceeds the threshold set by group_replication_compression_threshold , the transaction payload is compressed before being sent out to the group, and decompressed when it is received. Upon receiving a message, the member checks the message envelope to verify whether it is compressed or not. If needed, then the member decompresses the transaction, before delivering it to the upper layer. This process is shown in the following figure. 3776