[MAPREDUCE-6758] TestDFSIO should parallelize its creation of control files on setup

• Type: Improvement
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Component/s: test
• Assignee: Unassigned
• Reporter: Dennis Huo
• Created: 17/Aug/16 01:56
• Updated: 29/Jan/20 19:05

Description

TestDFSIO currently performs a sequential for-loop to create nrFiles control files in the controlDir which is a subdirectory of the overall test.build.data directory, which may be a non-HDFS FileSystem implementation:

private void createControlFile(FileSystem fs,
                                long nrBytes, // in bytes
                                int nrFiles
                              ) throws IOException {
  LOG.info("creating control file: "+nrBytes+" bytes, "+nrFiles+" files");

  Path controlDir = getControlDir(config);
  fs.delete(controlDir, true);

  for(int i=0; i < nrFiles; i++) {
    String name = getFileName(i);
    Path controlFile = new Path(controlDir, "in_file_" + name);
    SequenceFile.Writer writer = null;
    try {
      writer = SequenceFile.createWriter(fs, config, controlFile,
                                         Text.class, LongWritable.class,
                                         CompressionType.NONE);
      writer.append(new Text(name), new LongWritable(nrBytes));
    } catch(Exception e) {
      throw new IOException(e.getLocalizedMessage());
    } finally {
      if (writer != null)
        writer.close();
      writer = null;
    }
  }
  LOG.info("created control files for: "+nrFiles+" files");
}

When testing in an object-store based filesystem with higher round-trip latency than HDFS (like S3 or GCS), this means job setup that might only take seconds in HDFS ends up taking minutes or even tens of minutes against the object stores if the test is using thousands of control files. In the same vein as other JIRAs in https://issues.apache.org/jira/browse/HADOOP-11694, the control-file creation should be parallelized/multithreaded to efficiently launch large TestDFSIO jobs against FileSystem impls with high round-trip latency but which can still support high overall throughput/QPS.

Issue Links

• relates to: MAPREDUCE-6674 configure parallel tests for mapreduce-client-jobclient