brokerRole=SYNC_MASTER is invalid

[iamqq23ue]

When I set brokerRole=SYNC_MASTER, send_ok should be returned after both master and slave have written. But if I start the master first, send messages for a long time, and then start the slave, it will take a while for the master to synchronize. I can still send messages successfully when the master and slave are out of sync. why?

[RongtongJin]

In this case, there is a big gap between the master and slave, and the client can still send, but it will return slave_ NOT_ AVAILABLE.

[iamqq23ue]

In this case, there is a big gap between the master and slave, and the client can still send, but it will return slave_ NOT_ AVAILABLE.

Since no matter whether you configure async_master or sync_master, you can send successfully（even return slave_ NOT_ AVAILABLE.） without waiting for the completion of slave synchronization, so what is the use of setting sync_master?