code: private void clearSwapDir() throws IOException {
          if (! m_blockPathMap.isEmpty()) {
              throw new IllegalStateException("Attempt to clear swap directory when "
                      + "there are still managed blocks; use releaseAllBlocks() instead");
          }
  
          try (DirectoryStream<Path> dirStream = Files.newDirectoryStream(m_largeQuerySwapPath)) {
              Iterator<Path> it = dirStream.iterator();
              while (it.hasNext()) {
                  Path path = it.next();
                  VoltFile.recursivelyDelete(path.toFile());
              }
          }
      }
docs: Cleans out the large_query_swap directory of all files.
  Large query intermediate storage and results do not persist
  across shutdown/startup.
  This method is to clean up any spurious files that may not have
  been deleted due to an unexpected shutdown.
  @throws IOException