public void forget() {
      hashMap = null;
      byteSegmentRef.reset(0, 0);
      hasRows = false;
      readIndex = 0;
      nextTailOffset = -1;
    }
Lets go of any references to a hash map.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/BytesBytesMultiHashMap.java