Coherence is organized as set of services. At the root is the Cluster service. A cluster is defined by the combination of multicast address and port. A TTL network packet time-to-live; that is, the number of network hops setting can restrict the cluster to a single computer, or the computers attached to a single switch. Under the cluster service are the various services that comprise the Coherence API.
These include the various caching services Replicated, Distributed, and so on and the Invocation Service for deploying agents to various nodes of the cluster.
Each instance of a service is named, and there is typically a default service instance for each type. The cache services contain named caches com. NamedCache , which are analogous to database tables—that is, they typically contain a set of related objects. See Chapter 6, "Introduction to Coherence Clusters," for more information on the cluster service as well the other cluster-based service provided by Coherence. This section provides an overview of the NamedCache API, which is the primary interface used by applications to get and interact with cache instances.
The following source code returns a reference to a NamedCache instance. The underlying cache service is started if necessary. This is similar to Servlet name mapping in a web container's web. Coherence's cache configuration file contains in the simplest case a set of mappings from cache name to cache scheme and a set of cache schemes.
By default, Coherence uses the coherence-cache-config. This can be overridden on the JVM command-line with -Dtangosol. This argument can reference either a file system path, or a Java resource path. Map —basic Map methods such as get , put , remove. ObservableMap —methods for listening to cache events. See Chapter 25, "Using Map Events". CacheMap —methods for getting a collection of keys as a Map that are in the cache and for putting objects in the cache.
Also supports adding an expiry value when putting an entry in a cache. QueryMap —methods for querying the cache. ConcurrentMap —methods for concurrent access such as lock and unlock. InvocableMap —methods for server-side processing of cache data. Cache keys and values must be serializable for example, java.
Furthermore, cache keys must provide an implementation of the hashCode and equals methods, and those methods must return consistent results across cluster nodes. This implies that the implementation of hashCode and equals must be based solely on the object's serializable state that is, the object's non-transient fields ; most built-in Java types, such as String , Integer and Date , meet this requirement.
Some cache implementations specifically the partitioned cache use the serialized form of the key objects for equality testing, which means that keys for which equals returns true must serialize identically; most built-in Java types meet this requirement as well. As a clustered implementation of java. Map with several added features queries, concurrency , but with no persistent backing a "side" cache. As a means of decoupling access to external data sources an "inline" cache. In this case, the application uses the NamedCache interface, and the NamedCache takes care of managing the underlying database or other resource.
Using an inline cache makes it very easy to avoid duplicating calculations. If the calculation is complete, the result is simply pulled from the cache. Since any serializable object can be used as a cache key, it is a simple matter to use an object containing calculation parameters as the cache key.
See Chapter 15, "Caching Data Sources" for more information on inline caching. Used when data must be persisted immediately, or when sharing a data source with other applications.
The trade-off is that data is not immediately persisted to disk; however, it is immediately distributed across the cluster, so the data survives the loss of a server. Furthermore, if the entire data set is cached, this option means that the application can survive a complete failure of the data source temporarily as both cache reads and writes do not require synchronous access the data source. To implement a read-only inline cache, you simply implement two methods on the com.
CacheLoader interface, one for singleton reads, the other for bulk reads. Coherence provides an abstract class com. AbstractCacheLoader which provides a default implementation of the bulk method, which means that you need only implement a single method: public Object load Object oKey. This method accepts an arbitrary cache key and returns the appropriate value object. AbstractCacheStore or implement the interface com. The complexity of the cluster is completely hidden from the user of the virtual cache.
By automatically and dynamically partitioning data, Coherence ensures continuous data availability and transactional integrity, even in the event of a server failure. Simply stated, Oracle Coherence is a peer-to-peer, high availability data grid that supports Extreme Scaling , Increased Performance and Improved Reliability for applications and middleware.
These factors are a crucial component to addressing the challenges faced by many applications today, which must grow and scale elastically, reduce back-end load on databases, applications and mainframes and operate in a vast landscape of the Cloud, Shared Services and custom applications all requiring low latency and reliable access to data. Every piece of software needs to provide benefits or we would not use it.
The benefits Coherence provides include high-profile items such as performance, reliability, scalability and availability. Coherence is middleware that uses its data grid capabilities to reliably manage data objects in memory across many servers. Coherence is a key component of Oracle's Cloud Application Foundation CAF , which provides the framework for building elastic, reliable and highly available cloud-based applications using Oracle Fusion Middleware.
Many Oracle Fusion Middleware products provide native integration with Coherence out of the box to provide linearly scalable, fault tolerant, in-memory data management. These include the following Oracle products:. Oracle EM provides detailed insight and visibility into the operations and performance of Coherence caches, nodes, and services.
In addition, operational teams can quickly correlate cluster nodes with the underlying hosts to determine CPU and memory utilization on those hosts to aide in the decision making process for scaling Coherence Clusters.
The Oracle Coherence Incubator project consists of a collection of examples, organized as Apache Maven modules, demonstrating advanced uses of Oracle Coherence. The project includes a collection of Oracle Coherence-based utilities, distributed computing and data-grid examples, third-party integration examples and implementations of commonly used software patterns. If you are a visual learner , check out the Oracle Coherence YouTube channel. Oracle Coherence as a stand-alone solution or part of the Oracle Cloud Application Foundation can provides great value to your organization if you are faced with the challenges around the performance, reliability, scalability and availability of data and applications within your enterprise.
If you have questions or would like more information on how Coherence can provide value to your organization, please contact us and we'll put you in touch with one of our Cloud Application Foundation CAF Implementation Specialists. Mythics is an award-winning systems integrator, consulting firm, managed services provider and elite Oracle resale partner representing the entire Oracle product line across cloud, software, support, hardware and engineered systems.
Visit our Careers page or view Our Open Opportunities page to learn more. All Rights Reserved. Features Coherence provides several core services including caching, analytics, transactions and events.
Coherence Docker Docker resources for Oracle Coherence Coherence Hibernate Hibernate 3. Coherence Incubator Incubating distributed computing and data-grid examples, third-party integration examples and implementations of commonly used software patterns. Oracle Bedrock A framework for the development, orchestration and testing of concurrent distributed applications, especially Coherence.
Previously Oracle Tools.
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