Introduction to Coherence :
Coherence is an in-memory data grid which helps eliminate single points of failure and single points of bottlenecks in an application by distributing application objects and logic across multiple physical servers.
– Coherence is bundled with WLS 10.3.3 and above.
– Make sure you download the Package Installer for WLS which includes Coherence.
Eg : ” Oracle WebLogic Server 11gR1 (10.3.5) + Coherence – Package Installer ” Or ” Oracle WebLogic Server 11gR1 (10.3.5) + Coherence + OEPE – Package Installer “
Link to download : http://www.oracle.com/technetwork/middleware/weblogic/downloads/wls-main-097127.html
– Default multicast address and port are different for every Coherence releases.
For Coherence 3.6.0
Default Multicast Address is : 18.104.22.168
Default Port is : 36000
For Coherence 3.7.0
Default Multicast Address is : 22.214.171.124
Default port is : 37000
Designing the address in this way ensures that different versions of Coherence do not inadvertently cluster with each other by default.
– Coherence ships with two command line applications for testing, namely :
* Cache server ( storage enabled ) — cache-server.cmd
* Cache client ( storage disabled ) — coherence.cmd
Coherence Features :
– Coherence is an ideal solution for applications that face explosive increase in user base and when rate of change is faster to re-architect systems
– Information is available in-memory(vs. storage) in a distributed environment. So no disk I/O delays involved.
– Data is fault tolerant hence reliable.
– Data is maintained as objects inside JVM ( stored in-memory )
– Continuous operation maintained without interruption of service or loss of data when servers fail.
– When JVM crashes no intervention required. Servers monitor the health of each other.
– Automatic Failover.
– No human intervention required to maintain cluster
– Avoid single point of failure and single point of bottleneck
– and many more……
Different Editions of Coherence :
– Oracle Coherence Standard Edition
– Oracle Coherence Enterprise Edition
– Oracle Coherence Grid Edition
Important terms :
Coherence Node – a Java process – it is an instance of coherence server – has well known ports and address to communicate with other nodes.
Coherence Cluster – Group of storage enabled cluster nodes – specified by a common cluster name
Coherence Client – Storage disabled nodes.
Coherence Server – Storage enabled nodes.
Cache – Local memory space that holds frequently requested data