public void clear() {
    // This will make the object completely unusable. Semantics of clear are not defined...
    this.writeBuffers.clear();
    this.refs = new long[1];
    this.keysAssigned = 0;
    this.numValues = 0;
  }
Number of bytes used by the hashmap.
There are two main components that take most memory: writeBuffers and refs
Others include instance fields: 100
@return number of bytes
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/BytesBytesMultiHashMap.java