public Multimap<String, TableName> getTablesByNamespace() {
      Multimap<String, TableName> tablesByNS = HashMultimap.create();
      for (TableName tn : tablesWithNamespaceQuotas) {
        tablesByNS.put(tn.getNamespaceAsString(), tn);
      }
      return tablesByNS;
    }
Returns a view of all tables that reside in a namespace with a namespace quota, grouped by
the namespace itself.
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/QuotaObserverChore.java