[ Thanks to Lee
Schlesinger for this link. ]
“In MySQL replication each participating server may be a master,
a slave, or both. Master servers handle database transactions and
write them to a binary log (binlog). Slaves connect to masters and
request copies of their binary logs. Servers can act both as master
and slave thanks to features such as different auto increment,
which sets the interval between successive column values.“Theoretically, it is possible to have more than two masters. In
such cases MySQL replicates changes in a circle. However, it is
very hard to maintain and troubleshoot such circular replication.
When the replication breaks (and such interruptions are unavoidable
in the long term) it’s hard to ensure the integrity of the
information and resume fast operation with all the data. MySQL’s
developers recommend using no more than two masters. The number of
MySQL slaves is not a concern, because slaves cannot make global
changes and cannot cause deployment-wide problems.”