@VisibleForTesting
    void writeSplit(int count, MRSplitProto mrSplit, Path filePath) throws IOException {
      long fileWriteStarted = Time.monotonicNow();
      try (FSDataOutputStream out = fs.create(filePath, false)) {
        mrSplit.writeTo(out);
      }
      LOG.debug("Split #{} event to output path: {} written in {} ms", count, filePath,
          fileWriteStarted - Time.monotonicNow());
    }
SplitSerializer is a helper class for taking care of serializing splits to the tez scratch dir
when a size criteria defined by "hive.tez.input.fs.serialization.threshold" is met.
It utilizes an ExecutorService for parallel writes to prevent a single split write operation
becoming the bottleneck (as write() is called from a loop currently).
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/HiveSplitGenerator.java