System APIs and plug-ins

A plug-in is a component that provides a function to the pluggable components, which include ObjectGrid and BackingMap. To most effectively use eXtreme Scale as an in-memory data grid or database processing space, you should carefully determine how best you can maximize performance with available plug-ins.

Introduction to plug-ins
A WebSphere® eXtreme Scale plug-in is a component that provides a certain type of function to the pluggable components that include ObjectGrid and BackingMap. WebSphere eXtreme Scale provides several plug points to allow applications and cache providers to integrate with various data stores, alternative client APIs and to improve overall performance of the cache. The product ships with several default, prebuilt plug-ins, but you can also build custom plug-ins with the application.
Event listeners
You can use the ObjectGridEventListener and MapEventListener plug-ins to configure notifications for various events in the eXtreme Scale cache. Listener plug-ins are registered with an ObjectGrid or BackingMap instance like other eXtreme Scale plug-ins and add integration and customization points for applications and cache providers.
Eviction
WebSphere eXtreme Scale provides a default mechanism for evicting cache entries and a plug-in for creating custom evictors. An evictor controls the membership of entries in each BackingMap. The default evictor uses a time to live (TTL) eviction policy for each BackingMap. If you provide a pluggable evictor mechanism, it typically uses an eviction policy that is based on the number of entries instead of on time.
Writing an index plug-in
With a MapIndexPlugin plug-in, or index, you can write custom indexing strategies that are beyond the built-in indexes that eXtreme Scale provides.
TransactionCallback plug-in
Use the TransactionCallback plug-in to customize versioning and comparison operations of cache objects when you are using the optimistic locking strategy.
Using a Loader
With an eXtreme Scale Loader plug-in, an ObjectGrid map can behave as a memory cache for data that is typically kept in a persistent store on either the same system or some other system. Typically, a database or file system is used as the persistent store. A remote Java™ virtual machine (JVM) can also be used as the source of data, allowing hub-based caches to be built using ObjectGrid. A loader has the logic for reading and writing data to and from a persistent store.
LogElement and LogSequence
When an application is making changes to a Map during a transaction, a LogSequence object tracks those changes. If the application changes an entry in the map, a corresponding LogElement object provides the details of the change.
Using eXtreme Scale with JPA
The Java Persistence API (JPA) is a specification that allows mapping Java objects to relational databases. JPA contains a full object-relational mapping (ORM) specification using Java language metadata annotations, XML descriptors, or both to define the mapping between Java objects and a relational database. A number of open-source and commercial implementations are available.
OptimisticCallback plug-in
Use the OptimisticCallback plug-in to customize versioning and comparison operations of cache objects when you are using the optimistic locking strategy.
ObjectTransformer plug-in
With the ObjectTransformer plug-in, you can serialize, deserialize, and copy objects in the cache for increased performance.
WebSphereTransactionCallback plug-in
When you use the WebSphereTransactionCallback plug-in, enterprise applications that are running in a WebSphere Application Server environment can manage ObjectGrid transactions.

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