Mysql database sync between two databases
three different approaches:
Classic client/server approach: don't put any database in the shops; simply have the applications access your server. Of course it's better if you set a VPN, but simply wrapping the connection in SSL or ssh is reasonable. Pro: it's the way databases were originally thought. Con: if you have high latency, complex operations could get slow, you might have to use stored procedures to reduce the number of round trips.
replicated master/master: as @Book Of Zeus suggested. Cons: somewhat more complex to setup (especially if you have several shops), breaking in any shop machine could potentially compromise the whole system. Pros: better responsivity as read operations are totally local and write operations are propagated asynchronously.
offline operations + sync step: do all work locally and from time to time (might be once an hour, daily, weekly, whatever) write a summary with all new/modified records from the last sync operation and send to the server. Pros: can work without network, fast, easy to check (if the summary is readable). Cons: you don't have real-time information.
SymmetricDS is the answer. It supports multiple subscribers with one direction or bi-directional asynchronous data replication. It uses web and database technologies to replicate tables between relational databases, in near real time if desired.
Comprehensive and robust Java API to suit your needs.
Replication is not very hard to create.
Here's some good tutorials:
http://www.ghacks.net/2009/04/09/set-up-mysql-database-replication/
http://dev.mysql.com/doc/refman/5.5/en/replication-howto.html
http://www.lassosoft.com/Beginners-Guide-to-MySQL-Replication
Here some simple rules you will have to keep in mind (there's more of course but that is the main concept):
- Setup 1 server (master) for writing data.
- Setup 1 or more servers (slaves) for reading data.
This way, you will avoid errors.
For example: If your script insert into the same tables on both master and slave, you will have duplicate primary key conflict.
You can view the "slave" as a "backup" server which hold the same information as the master but cannot add data directly, only follow what the master server instructions.
NOTE: Of course you can read from the master and you can write to the slave but make sure you don't write to the same tables (master to slave and slave to master).
I would recommend to monitor your servers to make sure everything is fine.
Let me know if you need additional help
Have a look at Schema and Data Comparison tools in dbForge Studio for MySQL. These tool will help you to compare, to see the differences, generate a synchronization script and synchronize two databases.