Calculating primary reason for slow operations

NAM uses an algorithm to identify the primary reason why operation time is slow.

When determining the reason for slowness, NAM reports slow operations dividing them among the following categories and their subcategories:

  • Application design
    • Number of components
    • redirect time
    • response size
    • request size
  • Client/3rd party
  • Data center
  • Network
    • latency
    • loss rate
    • other
  • Multiple reasons

Note that counters for the above categories take into account only successful operations. Failures and aborts are not taken into account.

You can tweak slow operations reporting by setting the thresholds globally or at the software service level.

View the results of the primary reason for slowness calculation on the Slow operation cause breakdown tab of the Operation explorer.

Operation time calculation

  • Server time is calculated for all hits in the operation.
  • Network time is the part of the operation time in which all the hits in simultaneous sessions were recognized either as request time or response time.
  • Idle time is not a performance indicator. It is more of a context descriptor. It indicates that the client waited with sending subsequent page hit requests, but from the NAM Probe point of view, it's difficult to determine what client was actually occupied with. It might have been the javascript processing in a browser, third-party content loaded by the client, or content from servers that are not within the scope of NAM Probe monitoring.

Depending on the type of communication, operation time is calculated as follows:

  • For operations as a sequence of hits in the same TCP Session:
    Operation time = server time + network time + idle time  
    
  • For operations as a collection of hits on simultaneous TCP sessions (hits overlapping):
    Operation time = server time + network time + idle time + other time  
    

In the case of simultaneous TCP sessions with hit overlapping in place, the operation time components are calculated using the following criteria:

  • Server time - Part of operation time in which all the hits in simultaneous sessions were recognized as server time.
  • Network time - Part of operation time in which all the hits in simultaneous sessions were recognized as request time or response time.
  • Idle time - The sum of client idle times between hits.
  • Other time - Time that cannot be exclusively attributed to server time, network time, or idle time as a result of hits overlapping. Note that the metric is not calculated for simple operations completed in a single TCP session.

Here is a simplified example of overlapping hits in an operation with simultaneous TCP session and how the operation time components are determined.

We use Other time because sometimes it is impossible to attribute the portion of time explicitly to a particular time component when hits in simultaneous TCP sessions overlap. This way, we are still able to provide the most accurate possible values of the operation time components under the circumstances of hit overlapping.

Operation time does not include the time spent on TCP and SSL session establishment. The NAM Server provides the TCP SYN time metric that you can use to monitor the TCP handshake times.

The bounce chart below is a detailed look into the calculation of operation time components. Note that the chart includes just the portion of the client-server communication significant to this discussion.

NAM operation time calculation