[jira] [Created] (HDFS-8163) Using monotonicNow for block report scheduling causes test failures on recently restarted systems

["Arpit Agarwal (JIRA)" <ji...@apache.org>]

Arpit Agarwal created HDFS-8163:
-----------------------------------

             Summary: Using monotonicNow for block report scheduling causes test failures on recently restarted systems
                 Key: HDFS-8163
                 URL: https://issues.apache.org/jira/browse/HDFS-8163
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: datanode
    Affects Versions: 2.6.1
            Reporter: Arpit Agarwal
            Priority: Blocker


{{BPServiceActor#blockReport}} has the following check:

{code}
  List<DatanodeCommand> blockReport() throws IOException {
    // send block report if timer has expired.
    final long startTime = monotonicNow();
    if (startTime - lastBlockReport <= dnConf.blockReportInterval) {
      return null;
    }
{code}

Many tests set lastBlockReport to zero to trigger an immediate block report via {{BPServiceActor#triggerBlockReportForTests}}. However if the machine was restarted recently then this startTime could be less than {{dnConf.blockReportInterval}} and the block report is not sent.

{{Time#monotonicNow}} uses {{System#nanoTime}} which represents time elapsed since an arbitrary origin. The time should be used only for comparison with values returned by {{System#nanoTime}}.



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