Memory-to-memory session partitions

In a replication domain, by default, sessions are replicated to all the servers that are connected to the same replication domain. This replication can be redundant if a large number of servers are located in a replication domain.

Group partitioning
The session management facility has an option to partition the servers into groups when storing sessions. From the session replication perspective, you can view the replicator as having n groups or partitions. The default is 10 groups (the recommended minimum for performance reasons). The number of groups is global for the entire replication domain and all the session managers connected into the replication domain through any of the replicators in that domain.
By default, the session management facility running in server mode listens to all the partitions on the replicator. When a session is created in this facility, it is written to one of the partitions on the replicator through a round-robin assignment performed by the session manager. At the session manager level, you can configure the session manager (when in either server or both mode) to listen to a subset of the group (by default, the session manager listens to all of them). Therefore, you can reduce or partition where the HTTP sessions get replicated. Also note that becasue a session manager listens to a subset of the groups, it does not mean that those are the only groups it replicates sessions on. The session manager round robins over all the groups being listened to by the complete set of session managers connected to the replication domain.
In a cluster environment with a large number of servers, some servers can be configured to listen on some partitions and others on a different partition. All the servers are still logically linked together through the replicator domain and you can retrieve a session in any server in the cluster. The number of groups of the replication domain is set under manage internal replication in the Environment tab. Configure which groups and partitions a specific Session Management facility listens to under session management.
Single replica partitioning
The alternative to group partitioning is to replicate the session to only one other server. When this option is chosen, a session manager dynamically picks another session manager that is connected to the same replication domain to replicate the HTTP session to during session creation. All updates to the session are only replicated to that single server. A round-robin algorithm is employed over the eligible session manager instances. The round robin will not include selection of other session managers in the same Java virtual machine (JVM), or other JVMs on the same node unless there is only 1 node connected to the replication domain. Because this is set at the replication domain level, every session manager connected to this replication domain uses single replica replication. The mode of the session manager has the same meaning, that is, clients only send out changes to one other session manager (albeit not in the same JVM or node), servers only receive, and session managers in both mode, send and receive changes.

Related concepts
Memory-to-memory replication



Searchable topic ID:   cprs_m2m_partiton
Last updated: Jun 21, 2007 9:56:50 PM CDT    WebSphere Application Server for z/OS, Version 5.0.2
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