restore from replication

[Doug]

Hello,

Currently my master db has about 50G data.
There is a replication slave db, it's running with read-only mode.
When the master is down for some reasons, I will have to remove the
read-only flag in slave mysql and let the applications access to slave
with both read and write.
When the master is up again, how will I restore those data new updated
into slave to master?


Thank you.

Regards,
Doug