Migration of a Chosen Architectural Pattern to Service Oriented ...

Chapter 5. Guidelines 120How to: Reduces memory load of a stateful service by deferring their statesto a specially designed repositories like databases. State deferring requiresadditional effort related to memory load controlling as well as state storingand recovering, but it may occur crucial for performance. Access to deferringmechanism should be enabled via Canonical Resource [32]. Literatureprovides two possible ways for state deferring. First, (Partial State Deferral)describes storing of state of services in databases, while second (ServiceGrid) introduces Grids - an alternative for database state storage(a) Partial State Deferral [32]assumes deferring of only a part of the service’sstate. The deferred state will be no longer used in the process.Implementation of State deferring mechanisms should be consideredwhen all the processes are identified (see figure 5.11) This will allowthe process service to remain statefull and reduce memory load in thesame time. In order to fully leverage state deferring pattern, parts ofthe process that uses the same data should be executed in a sequenceif it is possible. For instance a process invokes firstly only servicesmanipulating on one part of a message, then a partial result is storedin database and process manipulates the next part of the message.(b) Service Grid [32]proposes an alternative for state storage. In oppositeto a typical database-based, Service Grid proposes state storage in aspecial dedicated grid of services. The grid contains many services thatare synchronized in order to provide security. Besides all the benefitsrelated to state deferring and alternative storage solution, Service Gridhas one significant drawback. It is vendor dependent. Grid has to beintegrated with SOA infrastructure - typically infrastructure providedby vendor of the grid.Introduction of State Deferring mechanism is always associated with performancereduction, thereupon the pros and cons of the mechanism should becarefully considered. Nevertheless application of State Repository may payoff when a process is very long or asynchronous. In case of asynchronousprocesses, final states can be stored and returned once (a few results) insteadof a few single returns.12. Identify current points of access to the migrated systemApplied SOA pattern: FrontendsHow to: Available literature presents this part of migration as a complexactivity that is not limited only to “separate clients” task. According to[2],Presentation Layer is a complex entity that is broken into three separatedelements: