On the slave server this appears when I run
State: Has read all relay log; waiting for the slave I/O thread to update it
The slave servers don't accept more queries from the application.
Any idea why MySQL is doing this?
That there are no changes on the Master node and the slave wait for changes.
so "has read all realay log" he has read all of them. Now he wait the there something happen on the Master node and he can fetch any changes from the master.