Gross hack to "re-master" or "re-parent" MySQL hosts before 4.1.1
which has the wonderful "SLAVE START UNTIL" command. (the UNTIL part is new)
Basically, if you have B and C both replicating from A, how do you make C
replicate from B instead of A?
-- can't touch A.
-- can't copy files from A or B to C, since C is a different file format
(InnoDB instead of MyISAM)
Keep watching the replication position of B and C until they're the same.
Then stop the replication thread in both, verify they're still the same,
then make C feed off B instead. (this requires that B is already setup
to log-master-updates and log-bin)
Go ugly hacks!
(There's a lot of LJ-specific code in here, but you should figure out
what it does and how to write a non-LJ equivalent. Like, DBI->connect
instead of the LJ-low-level $LJ::DBIRole->get_dbh_conn)