17 December 2009 - 17:10Replication of data and replication of functionality

From my experience I see that replication of data usually helps deal with performance problems, but that sometimes this replication involves replication of functionality, sometimes you end-up replicating some data on a different system (let’s call this the client system) and then you find yourself needing to code on the client system some piece of business logic which resides on the system from where data comes originally from (let’s call this system the master system).

More often than not this is a pretty scenario, because every modification to the business logic done on the master system has to be re-coded on the client system. Sometimes you find that you need to coordinate the releases of these 2 separate systems in order make the whole picture functionally consistent. One way to avoid re-coding the business logic on the client system is to expose the business logic on the master system thru some remoting mechanism (EJBs, Hessian, etc…) and then have the client system pass the data that it replicated locally to the master system in a synchronous call. While this solves the fact having the same business logic reside in 2 places it makes the client system dependent on the master system (*).

One solution to the above conundrum that is to replicate the data, along with the results of carrying out that piece of business logic on that data, to the client system. With this arrangement the client system does not need to have the master system up and running and it also does not need to re-code the same business logic inside. If you manage to use this (this approach doesn’t work in all cases) you will find yourself exporting business logic asynchronously by exporting both data and the results of carrying out that business logic on the data.

If I don’t write another post till January I wish you a Happy New Year!!!!!

* There is a physical dependency (the client systems needs the master system up and running for it to service calls) and possibly a library depedency which may couple the release cycles of these 2 systems (if the client system communicates with the master system thru objects rather than thry wire protocols you will need to synchronize the release cycles of these 2 systems in order to make sure that the client system doesn’t run in PROD with obsolete libraries).