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What is it?

An external, end-to-end view about the performance of ozone views. As an example:

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With tracing you can identify the slow components during an end-to-end test and go forward with Java Profiler on the identified component.

In this picture we can see that the OM/SCM calls are pretty fast but we have some problem on the freon side before the first writeChunk call.

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Until we will have a final Hadoop-wide solution we propagate the tracing id in our protobuf messages. For example this is the beginning of the OzoneManagerProtocol.proto

message OMRequest {
  required Type cmdType = 1; // Type of the command

  // A string that identifies this command, we generate  Trace ID in Ozone
  // frontend and this allows us to trace that command all over ozone.
  optional string traceID = 2;

  required string clientId = 3;

  

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For example this is the serialization from a ClientSideTranslator. It uses the TracingUtil class and it create a String from the current tracing information.

OMRequest payload = OMRequest.newBuilder(omRequest)
    .setTraceID(TracingUtil.exportCurrentSpan())
    .build();

To deserialize it on the server side:

Scope scope = TracingUtil
    .importAndCreateScope(request.getCmdType().name(), request.getTraceID());
try {
  //do the work here
} finally {
  scope.close();
}

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