Server System with scalable session timeout mechanism

A session manager has a session timeout mechanism to selectively timeout client-server sessions. The session timeout mechanism has multiple timeout buckets to hold corresponding groups of sessions according to the sessions' timeout periods. Sessions located in different ones of the timeout buckets are set to timeout at different times. The session manager also has a session timeout clock that is incremented every predetermined time unit (e.g., every minute). The session timeout clock maintains a pointer to one of the timeout buckets and advances that pointer with each clock increment. The session timeout clock advances the pointer through all of the timeout buckets, one bucket at a time. The session timeout clock advances the pointer repeatedly through all the buckets. The cycle time for the session timeout clock to reference every timeout bucket is equal to the incremental time unit multiplied by the number of buckets. A new session (or one that recently received a request and is restarting its timeout period) is inserted into a timeout bucket that is one or more buckets ahead of the clock pointer, depending upon the session's timeout period. When the timeout clock references a particular bucket, the sessions in that bucket are analyzed for possible timeout. Sessions whose timeout period has run without receiving any new requests are timed out and removed from the bucket.