code: private void executeUpdateColumnFamily(Tree statement)
      {
          if (!CliMain.isConnected() || !hasKeySpace())
              return;
  
          String cfName = CliCompiler.getColumnFamily(statement, currentCfDefs());
  
          try
          {
              // request correct cfDef from the server (we let that call include CQL3 cf even though
              // they can't be modified by thrift because the error message that will be thrown by
              // system_update_column_family will be more useful)
              CfDef cfDef = getCfDef(thriftClient.describe_keyspace(this.keySpace), cfName, true);
  
              if (cfDef == null)
                  throw new RuntimeException("Column Family " + cfName + " was not found in the current keyspace.");
  
              String mySchemaVersion = thriftClient.system_update_column_family(updateCfDefAttributes(statement, cfDef));
              sessionState.out.println(mySchemaVersion);
              keyspacesMap.put(keySpace, thriftClient.describe_keyspace(keySpace));
          }
          catch (InvalidRequestException e)
          {
              throw new RuntimeException(e);
          }
          catch (Exception e)
          {
              throw new RuntimeException(e);
          }
      }
docs: Update existing column family identified by name
  @param statement - tree represeting statement