Cleanup memory when a dataset has been dropped.
diff --git a/asterix-common/src/main/java/edu/uci/ics/asterix/common/context/DatasetLifecycleManager.java b/asterix-common/src/main/java/edu/uci/ics/asterix/common/context/DatasetLifecycleManager.java
index 90fcf87..9cbdb81 100644
--- a/asterix-common/src/main/java/edu/uci/ics/asterix/common/context/DatasetLifecycleManager.java
+++ b/asterix-common/src/main/java/edu/uci/ics/asterix/common/context/DatasetLifecycleManager.java
@@ -150,6 +150,8 @@
                 used -= (vbc.getNumPages() * vbc.getPageSize());
             }
             datasetInfos.remove(did);
+            datasetVirtualBufferCaches.remove(did);
+            datasetOpTrackers.remove(did);
         }
 
     }