@Override public synchronized boolean dropProperties(String mapKey) {
    boolean m = properties.remove(mapKey) != null;
    boolean d = digests.remove(mapKey) != null;
    return m & d;
  }
The digests for the stored maps.
standalone-metastore/metastore-common/src/test/java/org/apache/hadoop/hive/metastore/properties/TransientPropertyStore.java