Update trace example in documentation (triton-inference-server#4951)

* Update trace example in  documentation

* Add brief description on new trace options

docs/user_guide/trace.md

@@ -33,15 +33,21 @@ individual inference requests. Tracing is enable by command-line
 arguments when running the tritonserver executable. For example,
 
 ```
-$ tritonserver --trace-file=/tmp/trace.json --trace-rate=100 --trace-level=TIMESTAMPS ...
+$ tritonserver --trace-file=/tmp/trace.json --trace-rate=100 --trace-level=TIMESTAMPS \
+    --log-frequency=50 --trace-count=100 ...
 ```
 
 The --trace-file option indicates where the trace output should be
 written. The --trace-rate option specifies the sampling rate. In
 this example every 100-th inference request will be traced. The
 --trace-level option indicates the level of trace detail that should
 be collected. --trace-level option may be specified multiple times to 
-trace multiple informations. Use the --help option to get more information.
+trace multiple informations. The --log-frequency option specifies the rate that
+the traces are written to file. In this example Triton will log to file for
+every 50 traces collected. The --trace-count option specifies the remaining 
+number of traces to be collected. In this example Triton will stop tracing more
+requests after 100 traces are collected.
+Use the --help option to get more information.
 
 In addition to configure trace settings in command line arguments, The user may
 modify the trace setting when Triton server
@@ -63,20 +69,21 @@ The trace output is a JSON file with the following schema.
     "model_name": $string,
     "model_version": $number,
     "id": $number
-    "parent_id": $number,
+    "parent_id": $number
+  },
+  {
+    "id": $number,
     "timestamps": [
-      { "name" : $string, "ns" : $number },
-      ...
+      { "name" : $string, "ns" : $number }
     ]
   },
   {
-    "model_name": $string,
-    "model_version": $number,
     "id": $number
     "activity": $string,
     "tensor":{
       "name": $string,
       "data": $string,
+      "shape": $string,
       "dtype": $string
     }
   },
@@ -87,30 +94,37 @@ The trace output is a JSON file with the following schema.
 Each trace is assigned a "id", which indicates the model name and 
 version of the inference request. If the trace is from a
 model run as part of an ensemble, the "parent_id" will indicate the
-"id" of the containing ensemble.  
+"id" of the containing ensemble.
+For example:
+```
+[
+  {
+    "id": 1,
+    "model_name": "simple",
+    "model_version": 1
+  },
+  ...
+]
+```
 
 Each `TIMESTAMPS` trace will have one or more "timestamps" with 
 each timestamp having a name and the timestamp in nanoseconds ("ns"). 
 For example:
 
 ```
 [
-  {
-    "model_name": "simple",
-    "model_version": -1,
-    "id": 1,
-    "timestamps" : [
-      { "name": "http recv start", "ns": 2259961222771924 },
-      { "name": "http recv end", "ns": 2259961222820985 },
-      { "name": "request handler start", "ns": 2259961223164078 },
-      { "name": "queue start", "ns": 2259961223182400 },
-      { "name": "compute start", "ns": 2259961223232405 },
-      { "name": "compute end", "ns": 2259961230206777 },
-      { "name": "request handler end", "ns": 2259961230211887 },
-      { "name": "http send start", "ns": 2259961230529606 },
-      { "name": "http send end", "ns": 2259961230543930 }
-    ]
-  }
+  {"id": 1, "timestamps": [{ "name": "HTTP_RECV_START", "ns": 2356425054587444 }] },
+  {"id": 1, "timestamps": [{ "name": "HTTP_RECV_END", "ns": 2356425054632308 }] },
+  {"id": 1, "timestamps": [{ "name": "REQUEST_START", "ns": 2356425054785863 }] },
+  {"id": 1, "timestamps": [{ "name": "QUEUE_START", "ns": 2356425054791517 }] },
+  {"id": 1, "timestamps": [{ "name": "INFER_RESPONSE_COMPLETE", "ns": 2356425057587919 }] },
+  {"id": 1, "timestamps": [{ "name": "COMPUTE_START", "ns": 2356425054887198 }] },
+  {"id": 1, "timestamps": [{ "name": "COMPUTE_INPUT_END", "ns": 2356425057152908 }] },
+  {"id": 1, "timestamps": [{ "name": "COMPUTE_OUTPUT_START", "ns": 2356425057497763 }] },
+  {"id": 1, "timestamps": [{ "name": "COMPUTE_END", "ns": 2356425057540989 }] },
+  {"id": 1, "timestamps": [{ "name": "REQUEST_END", "ns": 2356425057643164 }] },
+  {"id": 1, "timestamps": [{ "name": "HTTP_SEND_START", "ns": 2356425057681578 }] },
+  {"id": 1, "timestamps": [{ "name": "HTTP_SEND_END", "ns": 2356425057712991 }] }
 ]
 ```
 
@@ -122,13 +136,12 @@ including its "name", "data" and "dtype". For example:
 ```
 [
   {
-    "model_name": "simple",
-    "model_version": -1,
     "id": 1,
     "activity": "TENSOR_QUEUE_INPUT",
     "tensor":{
       "name": "input",
       "data": "0.1,0.1,0.1,...",
+      "shape": "1,16",
       "dtype": "FP32"
     }
   }