[HDFS-13994] Improve DataNode BlockSender waitForMinLength

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.2.0
• Fix Version/s: 3.3.0
• Component/s: datanode
• Hadoop Flags: Reviewed
• Flags: Patch
• Assignee: David Mollitor
• Reporter: David Mollitor
• Created: 15/Oct/18 17:37
• Updated: 19/Oct/18 18:19
• Resolved: 19/Oct/18 17:36

Description

BlockSender.java

  private static void waitForMinLength(ReplicaInPipeline rbw, long len)
      throws IOException {
    // Wait for 3 seconds for rbw replica to reach the minimum length
    for (int i = 0; i < 30 && rbw.getBytesOnDisk() < len; i++) {
      try {
        Thread.sleep(100);
      } catch (InterruptedException ie) {
        throw new IOException(ie);
      }
    }
    long bytesOnDisk = rbw.getBytesOnDisk();
    if (bytesOnDisk < len) {
      throw new IOException(
          String.format("Need %d bytes, but only %d bytes available", len,
              bytesOnDisk));
    }
  }
 

It is not very efficient to poll for status in this way. Instead, use notifyAll within the ReplicaInPipeline to notify the caller when the replica has reached a certain size.