Request metric extension

 

Certain applications might require additional instrumentation points within the request metrics flow. For example, you might want to understand the response time to a unique back-end system as seen in the following call graph:

HTTP request /trade/scenario             ------------------------------> 172 ms
     Servlet/trade/scenario          --------------------------------> 130 ms
        Servlet/call to unique back-end system -------------------------->38 ms

Request metrics uses a token or correlator when tracing the flow of each request through the system. To create the call graph above with this instrumentation, plug into that flow of the request and issue the appropriate Application Response Measurement (ARM) API for an ARM agent to collect the data and for the ARM vendor to create the call graph. Request metrics exposes the Correlation Service API for you to plug into the flow of the request. The following example is one of the typical flows that might be followed by an instrumented application to plug into the request metrics flow:

1. Create a new ArmTransaction object, which runs various instrumentation calls such as start or stop. The Correlation Service Arm wrapper (PmiRmArmTx) encapsulates this object before being inserted into the request metrics flow.

2. Populate the ArmTransaction object with an appropriate ArmCorrelator object. This object encapsulates the actual ARM correlator bytes.

3. Run the start method on the ArmTransaction object, marking the beginning of the instrumented method.

4. Instantiate a PmiRmArmTx object using the static method on the PmiRmArmTxFactory class, and populate it with the ArmTransaction object above.

5. Pass the PmiRmArmTx object above to the Correlation Service by pushing it onto the Correlation Service stack using exposed methods on the PmiRmArmStack class.

6. Perform the tasks that need to be done by the method being instrumented. The Correlation Service takes care of flowing the ArmTransaction object as necessary, which eventually results in the call graph view of the transaction times.

7. At the end of the instrumented method, access the PmiRmArmTx object from the Correlation Service using exposed methods on the PmiRmArmStack class, access the ArmTransaction object and perform a stop to indicate the end of the transaction.

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Sub-topics

Example: Using the correlation service interface

 

Related tasks

Monitor application flow