I believe Gowtham's response is accurate. If the link goes down it is going to unclear which update becomes the final one, and it will be possible for one side to contain the row after one update, and the other to contain the row after the other update, thus being out of sync.
Mysql has no support for resolving these types of conflicts so you would need to ensure updates are done in a safe manner at the application level. As far as inserts an autoincrement collumns are concerned one way to handle it is to use a unique server id and create a combined key (auto_increment_field, server_id). If all you really need is a failover server and you don't need to do active/active load balancing then you can avoid these type of update issues fairly easily. As for whitepapers, I'm not aware of any good ones, but the replication FAQ in the mysql manual provides a good starting point for this type of 2 way replication setup. John -----Original Message----- From: Gowtham Jayaram [mailto:[EMAIL PROTECTED] Sent: Monday, March 01, 2004 1:22 PM To: [EMAIL PROTECTED] Subject: Re: Replication / Synchronizing DB across different machines >> But what happens if there is a break of >> communication and the same record on both machines >> is modified? For example, if the sync link is ? >> down, and I update record #1 on A, while at the >> same time, another user is modifying record #1 on >> server B. When the link comes back online, how >> will the servers be able to synchronize record #1, >> or in the case that this is impossible (I can't >> even imagine how I would do that manually - merge? >> A overwrite B? B overwrite A?), how does MySQL >> flag it and let me know that there is a discrepancy >> in the two DBs? >From my understanding (please bear in mind I am new to MySQL replication); MySQL Replication does not support conflict resolution. So in the sceanrio wherein you have dual masters actively updating the same data the conflict resolution onus falls on the Application using MySQL process. Also, there is no need for the link between 'A' and 'B' to go down for this issue to surface. The fact that you have a dual-master setup is reason enough for the problem you have explained above to surface. Gowtham __________________________________ Do you Yahoo!? Get better spam protection with Yahoo! Mail. http://antispam.yahoo.com/tools -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
