6.4.3. Replication Slave SQL Thread States
The following list shows the most common states you may see in
State column for a slave server SQL
Reading event from the relay log
The thread has read an event from the relay log so that the
event can be processed.
Has read all relay log; waiting for the slave I/O
thread to update it
The thread has processed all events in the relay log files,
and is now waiting for the I/O thread to write new events to
the relay log.
Waiting for slave mutex on exit
A very brief state that occurs as the thread is stopping.
State column for the I/O thread may also
show the text of a statement. This indicates that the thread has
read an event from the relay log, extracted the statement from
it, and is executing it.