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22.2.2. HttpSession Passivation and Activation
Passivation is the process of controlling memory usage by removing relatively unused sessions from memory while storing them in persistent storage. If a passivated session is requested by a client, it can be "activated" back into memory and removed from the persistent store. JBoss Enterprise Application Platform 5 supports passivation of HttpSessions from web applications whose
web.xml includes the distributable tag (i.e. clustered web applications).
Passivation occurs at three points during the lifecycle of a web application:
- When the container requests the creation of a new session. If the number of currently active sessions exceeds a configurable limit, an attempt is made to passivate sessions to make room in memory.
- Periodically (by default every ten seconds) as the JBoss Web background task thread runs.
- When the web application is deployed and a backup copy of sessions active on other servers is acquired by the newly deploying web application's session manager.
A session will be passivated if one of the following holds true:
- The session has not been in use for longer than a configurable maximum idle time.
- The number of active sessions exceeds a configurable maximum and the session has not been in use for longer than a configurable minimum idle time.
In both cases, sessions are passivated on a Least Recently Used (LRU) basis.
22.2.2.1. Configuring HttpSession Passivation
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Session passivation behavior is configured via the
jboss-web.xml deployment descriptor in your web application's WEB-INF directory.
- max-active-sessionDetermines the maximum number of active sessions allowed. If the number of sessions managed by the the session manager exceeds this value and passivation is enabled, the excess will be passivated based on the configured
passivation-min-idle-time. If after passivation is completed (or if passivation is disabled), the number of active sessions still exceeds this limit, attempts to create new sessions will be rejected. If set to-1(the default), there is no limit. - use-session-passivationDetermines whether session passivation will be enabled for the web application. Default is
false. - passivation-min-idle-timeDetermines the minimum time (in seconds) that a session must have been inactive before the container will consider passivating it in order to reduce the active session count to obey the value defined by
max-active-sessions. A value of-1(the default) disables passivating sessions beforepassivation-max-idle-time. Neither a value of-1nor a high value are recommended ifmax-active-sessionsis set. - passivation-max-idle-timeDetermines the maximum time (in seconds) that a session can be inactive before the container should attempt to passivate it to save memory. Passivation of such sessions will take place regardless of whether the active session count exceeds
max-active-sessions. Should be less than theweb.xmlsession-timeoutsetting. A value of-1(the default) disables passivation based on maximum inactivity.
The total number of sessions in memory includes sessions replicated from other cluster nodes that are not being accessed on this node. Take this into account when setting
max-active-sessions. The number of sessions replicated from other nodes will also depend on whether buddy replication is enabled.
Say, for example, that you have an eight node cluster, and each node handles requests from 100 users. With total replication, each node would store 800 sessions in memory. With buddy replication enabled, and the default
numBuddies setting (1), each node will store 200 sessions in memory.
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