0ed2c426_3____The_ClusterManager_object__Attribute
[Description] The length of session ids created by this Manager, measured in bytes, excluding subsequent conversion to a hexadecimal string and excluding any JVM route information used for load balancing. The default is 16. You should set the length on a nested SessionIdGenerator element instead. [Attribute] 
sessionIdLength
Apache Tomcat 7 Configuration Reference (7.0.63) - The ClusterManager object