Introduction
This Guide describes how the OnDemand Agents work for Apica LoadTest (ALT) , and tips not to not overload them.
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The typical subscription for an ALT customer is “OnDemand”“OnDemand.” |
Locations
Location Map | OnDemand Agent Locations |
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When you set up a load test, you choose from a set of locations , from where you want to run your load test:  | Each location has a number of several available OnDemand Agents.  |
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OnDemand Agents
On the following link, you can find up-to-date information about locations and agents:
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Each of these conditions calls for More/Higher CPUs:
The number of calls per “page”“page.”
Higher calls
If calls are made in “parallel” or “serial”“serial.”
Parallel Calls
The think time (pause) between each “page”“page.”
Shorter Think Times
The response times of the called resources
Shorter Response Time
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When an Agent is overloaded (e.g., CPU > 90%), it will limit the throughput, and the returned performance data will be wrong (too low). |
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1. Compare Response Times
Loop Time > Page Times = Agent Overload
The typical symptom of an overloaded Agent is that the total duration of a test iteration (“loop time”) is clearly longer than the sum of the “page times”times.”
This is because not all execution time is included in the page times. For instance, SSL handshakes, HTTP handshakes, and garbage collection.
When the Agent's CPU of the Agent is overused, these additional processes may take significant time for the agent to process so that they will be added to the Loop time but NOT the Page Time.
Example:
On the test “Overview” tab |
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, check the Average Response time Per Loop | Compare the Loop Response time to the Page Summary Total |
 Note: Session Time included Think Times |
Compare to this:
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 There was no difference; the Loop included each of the 5-page response times, so the Agent worked fine!
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Looking |
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at the detailed result file | |
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Once a job is finished, you can download the detailed result file and analyze it. In the “Jobs” view, click the download icon for the job you’re interested in. | |
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This will get you an xxx.prxres file. Put |
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that file in the ZebraTester/MyTests folder. Open the file in the ZebraTester UI/Project Navigator: |
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Then click the magnifying glass next to the Load Test name: |
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Then select the Diagram: Load Generator Performance: |
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Finally, look at the CPU Usage graph: |
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 In this example, the usage is very low, so we’re fine! |
2. Leverage SSL Cache Efficiencies
✅ More SSL Cache Hits Help Agent CPU
Check SSL Cache Efficiency and Percent time Spent on SSL. | |
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You can check for this in the result file (see the previous section) | |
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by selecting Diagram: SSL Cache Efficiency. |
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The example below |
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shows that a new SSL handshake was performed for |
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every request. This can be CPU intensive, so keep the SSL Cache-hits as high as possible; Offloading this to the cache keeps the Agent CPU lower. |
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Also, look at the Results per Page | URL (Details) view. Compare the numbers in the Av SSL/TLS column with the Av Time column. In the example below, about 10% of the time is spent on SSL. |
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Tips to Avoid Overloading Agents
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