apache/spark — pull request #3617 by guowei2 (2014-12-05 05:32:41+00:00)
Title: [SPARK-4756][SQL] FIX: sessionToActivePool grow infinitely, even as sessions expire

**sessionToActivePool** in **SparkSQLOperationManager** grow infinitely, even as sessions expire.
we should remove the pool value when the session closed, even though **sessionToActivePool** would not exist in all of sessions.