Memory-to-memory replication

WebSphere Application Server supports session replication to another WebSphere Application Server instance. This support is referred to as memory-to-memory session replication. In this mode, sessions can replicate to one or more WebSphere Application Server instances to address HTTP Session single point of failure (SPOF). This is a new alternative in IBM WebSphere Application Server, Version 5 to the existing saving of HTTP Session to a database.

The WebSphere Application Server instance in which the session is currently processed is referred to as the owner of the session. In a clustered environment, session affinity in the WebSphere Application Server plug-in routes the requests for a given session to the same server. If the current owner server instance of the session fails, then the WebSphere Application Server plug-in routes the requests to another appropriate server in the cluster. This server either retrieves the session from a server that has the backup copy of the session or it retrieves the session from its own backup copy table. The server now becomes the owner of the session and affinity is now maintained to this server.

When a session is created or updated in a WebSphere Application Server instance, the session is transferred (or replicated) through one of the replicator entries under the replication domain that is configured with the session management facility. This session potentially gets replicated to the WebSphere Application Server instances that are also connected to the same replicator domain. The mode and partitioning determine whether WebSphere Application Server instances in the same replication domain gets the session.

There are three possible modes. You can set up a WebSphere Application Server instance to run in:

You can select the replication mode of server, client, or both when configuring the session management facility for memory-to-memory replication. The default is both. This storage option is controlled by the mode parameter.

With respect to mode, the following are the primary examples of memory-to-memory replication configuration:

Although the administrative console allows flexibility and additional possibilities for memory-to-memory replication configuration, only the configurations provided above are officially supported.

In a cluster, by default, sessions are replicated in all the servers in the cluster that are connected to the same replicator domain. This replication can be redundant if a large number of servers exist in a cluster. The session management facility has an option to partition the servers into groups when storing sessions.


Related concepts
Replication
Memory-to-memory topology: Peer-to-peer function with a local replicator
Memory-to-memory topology: Peer-to-peer function with remote/isolated replicators
Memory-to-memory topology: Client/server function with remote replicators
Memory-to-memory topology: Client/server function with isolated replicators
Related tasks
Replicating data



Searchable topic ID:   cprsmemory
Last updated: Jun 21, 2007 4:55:42 PM CDT    WebSphere Application Server Network Deployment, Version 5.0.2
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