The implication of the number specified in the maxLocks property can be gauged by dividing the value of maxSessions with maxLocks. For example, if maxSessions = 1000 and you set maxLocks = 10, then approximately 100 sessions (1000/10) will contend for the same lock. Increasing maxLocks will reduce the number of sessions that contend for the same lock and may improve performance and reduce latency. However, increasing the number of locks also increases the number of open file descriptors, and reduces the number of available descriptors that would otherwise be assigned to incoming connection requests.
For more information about these settings, see the "Session Managers" chapter in the Sun Java System Web Server 6.1 SP6 Programmer’s Guide to Web Applications.