Shutdown of master in semisync when it's in sync can let more transactions in the master than the slaves.
This is expected in case of a crash as the binlog write before send and wait for the ACK. But this is an issue in case of regular shutdown, as the workload can not be safely be moved to a slave.
We can make sure the semi sync thread is killed last in shutdown and stopped only if status move to no sync or after receiving the ACK , this would possibly delay shutdown for the maximum time of the rpl_semi_sync_master_timeout
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Bug
Major
MDEV-28114 Semi-sync Master ACK Receiver Thread Can Error on COM_QUIT
MDEV-18450has partly fixed this issue. The remained work is to further delay the master shutdown until either an ackarrives or rpl_semi_sync_master_timeout elapses.