Haibin Huang created HDFS-15629:
-----------------------------------

             Summary: Add seqno when warning slow mirror/disk in BlockReceiver
                 Key: HDFS-15629
                 URL: https://issues.apache.org/jira/browse/HDFS-15629
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Haibin Huang


When client write slow, it will print a slow log from DataStreamer
{code:java}
if (ack.getSeqno() != DFSPacket.HEART_BEAT_SEQNO) {
  Long begin = packetSendTime.get(ack.getSeqno());
  if (begin != null) {
    long duration = Time.monotonicNow() - begin;
    if (duration > dfsclientSlowLogThresholdMs) {
      LOG.info("Slow ReadProcessor read fields for block " + block
          + " took " + duration + "ms (threshold="
          + dfsclientSlowLogThresholdMs + "ms); ack: " + ack
          + ", targets: " + Arrays.asList(targets));
    }
  }
}
{code}
here is an example:

Slow ReadProcessor read fields for block BP-XXX:blk_XXX took 2756ms 
(threshold=100ms); ack: seqno: 3341 status: SUCCESS status: SUCCESS status: 
SUCCESS downstreamAckTimeNanos: 2751531959 4: "\000\000\000", targets: [XXX, 
XXX, XXX][XXX, XXX, XXX]

There is an ack seqno in the log, so we can find which packet cause write slow. 
However, datanode didn't print the seqno in slow log, so we can't kown this 
packet write slow in which stage.

HDFS-11603 and HDFS-12814 add some slow warnings in BlockReceiver, i think we 
should add seqno in these slow warnings, in order to find the corresponding 
packet write slow in which stage.



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