<Robinson, Eric: 5/17/04 1048> >there is no mechanism for propagating slave changes >from the slave back up to the master... synchronization >occurs *only* from master to slave >(hence the terminology).
Then why do they call it 2-way replication? Is there such a thing as master-to-master? </Robinson, Eric> Eric, In order to declare a server a "master" server it must be able to accept INSERTs and UPDATEs without corrupting your data integrity. If you want to keep 2 "master" servers in sync, you must implement some form of distributed locking. Distributed locking is what keeps both servers from issuing the same ID number at the same time to two different records or permitting simultaneous updates to the same record on two different servers. Once you solve the issue of distributed transaction locking you are now able to keep both sets of data intact. The entire locking/communication cycle between two (or more) servers that ensures BOTH data integrity AND consistency is what is mean by the term "2-way replication". MySQL does not support distributed locking (yet). Until then, your data integrity is ensured ONLYif you allow inserts/updates on only 1 server at a time and copy the changes as they happen to all other servers that need copies of the data. If you have two servers, A and B, and your applications are written so that server A is where all of the data creation and changes occur then you can ensure that all new records will have unique primary key values and that each primary key value identifies the same data (you have achieved data consistency). Those new records could be copied over to B through the built-in replication system in near-real-time. This is the 1-way replication you have read so much about. Each master server (like A) can "push" data to multiple slaves (like B) but as of right now there is no way for separate MySQL servers to communicate with each other so that each of them can accept new or updated data while preventing loss of data consistency (2-way or n-way replication). I hope I helped you to understand that 2-way replication involves much more than simple data copying from server to server and requires an entire distributed transaction system in order to prevent data collisions and corruptions. MySQL will have it in a future release but it's ready for an initial alpha test, yet. Shawn Green Database Administrator Unimin Corporation - Spruce Pine -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
