public void flushAll() {
    try {
      flush();
    } catch (IOException ex) {
      throw new DiskAccessException(
          String.format("Failed writing key to %s", diskFile.getPath()),
          ex, parent);
    }
  }
Method to be used only for testing

@param ch Object to replace the channel in the Oplog.crf
@return original channel object
geode-core/src/main/java/org/apache/geode/internal/cache/OverflowOplog.java