All Things WebSphere

Concerns and issues relating to all versions of WebSphere Application Server

Thursday, August 18, 2011

WebSphere Session Persistence Best Practices ... The 10/10 Rule

10 Seconds write frequency /10 KB session size

The most important factor in session replication performance is the write frequency setting.
This setting should be carefully considered to determine if the environment needs full reliability and failover support (End of Servlet service), or if a time based frequency is sufficient. In testing done for this study, a value larger than 10 seconds rarely provided much additional benefit. Therefore, as a best practice, if the time based frequency is chosen, we would recommend a value of 10 seconds.

The cost of replication or persistence increases as the size of the session object increases.
Therefore, as a best practice, we would recommend keeping session sizes smaller than 10 KB.

Database session persistence performs better than Memory- to- Memory session persistence. This is because in the Database persistence mode, the application servers are not having to act as both an application server servicing requests and a replication backup, as was the case in the Memory-to-Memory scenarios. For larger environments, Database persistence is almost always the better choice as it scales a lot better than Memory-to-Memory.

There is an extra cost associated with a database server, license, and database administrator. Most environments require database backups / mirrors. The performance of the database can also be a bottleneck as the network latency between database and app server, and the speed of the database machine and disk drives are all factors. From a cost perspective Memory-to-Memory session persistence will always beat database persistence.

See this Whitepaper WebSphere Application Server V8 Replication Performance for a complete discussion of this topic and DayTrader benchmark results.

Labels: session