Synchronization of state with remote (continued...)

 Efficiency in data synchronization in these configurations and architectures come from determining what data changes, how to scope it and how to reduce the traffic associated with propagating the change.  It is customary to have a synchronization layer on the client, a synchronization middleware on the server, and a network connection during the synchronization process that supports bidirectional updates. The basic synchronization process involves the initiation of synchronization – either on demand or on a periodic basis, the preparation of data and its transmission to a server with authentication, the execution of the synchronization logic on the server side to determine the updates and the transformations, the persistence of the changed data over a data adapter to one or more data stores, the detection and resolution of conflicts and finally the relaying of the results of the synchronization back to the client application.

The choice of synchronization technique depends on the situation. One of the factors that plays into this is the synchronization mode.  There are two main modes of synchronization: snapshot and net change. Snapshots are the data as of a point of time. The data in a snapshot does not change. So it is useful to compare. This synchronization makes it possible to move large amount of data from one system to another. This is the case when the data has not changed at the remote location. Since snapshots might contain a large amount of data, a good network connection is required to transfer it. Updates to the product catalog or price list is a great use case for snapshot synchronization because the updates are collected in a snapshot, transferred and loaded at once on the destination store.

The net changes mode of synchronization can be considered slightly more efficient than the snapshot synchronization. In these cases, only the changed data is sent between the source and destination datastores and it reduces the network bandwidth and connection times. If the data were to change quite often on one server, only the initial and final state is required to create the changes that can then be made on the destination. Both the modes are bidirectional so the changes made in a local store can be propagated to the enterprise store. The net changes mode does not take into consideration the changes made in individual transactions. If those were important, the transaction log based synchronization may work better.

Transmission of data is also important in the effectiveness of synchronization technique. If an application is able to synchronize without the involvement of the user, it will work on any network – wired or wireless otherwise the latter usually requires human intervention to set up a connection. There are two types of data propagation methods – session based and message based. The session based synchronization method requires a direct connection. The updates can be done both ways and they can be acknowledged. The synchronization resumes even after a disruption. The point from which the synchronization resumes is usually the last committed transaction. The connection for this data propagation method can be established well in advance.

Message based synchronization requires the receiver to take the message and perform the changes. When this is done, a response is sent back. Messages help when there is no reliable network connection. The drawback is there is no control over when the messages will be acted upon and responded.