I have web application running on 4 client systems (users with login -password )and administered at one server (apache based server ,XAMP), when server is up web application will run normally . If for any reason (no internet connectivity etc) the client is unable to access the network , client should be able to use applcation without loss of data , so when the network is up , no loss synchronization should happen.
Depends on how complicated the update is. You can try INSERT IGNORE. Are you updating more than one table for each DB? Perhaps if you show the schemas. Are the PKs and FKs the same in remote and local versions?