If you're familiar with DevOps Test Performance, you've likely interacted with various log files. While Test Logs are a cornerstone of troubleshooting, Common Base Event logs often provide crucial insights that can be overlooked. These logs, generated by the playback engine, can provide crucial insights when Test Logs fall short.

Common Base Event Logs

When a user group runs locally, problem determination logs are stored within your workspace's deployment_root directory. This directory is specific to your user and contains multiple alphanumeric subdirectories for each test run.

If a user group runs on a remote location, the deployment directory is defined for that specific location. You can find this directory listed on the "Locations" page within the DevOps Test Performance platform.

The problem determination logs are typically located in the deployment_root directory of your workspace

Within the deployment directory, you'll find subdirectories with unique GUIDs (Globally Unique Identifiers) representing individual test runs.

The problem determination logs are stored within these GUID directories. You can search for files with the CommonBaseEvent extension to locate them.

General Details

Navigate to the deployment directory for the agent machine where the test was executed, within the deployment directory you'll find multiple alphanumeric directories representing different test runs. Look for the directory with a timestamp that corresponds to the time of the execution you're interested in. Inside the execution data directory, locate the CommonBaseEvents##, where ## represents a sequential number. These log files contain detailed information about the test run, including events, errors, and warnings.

A Case Study

Problem 1:

We encountered the "java.lang.IllegalArgumentException: Could not read file header line for file" error while working with CSV files in our JMeter tests.

Analysis:

• By examining the Common Base Event logs, we discovered that the error was occurring specifically when trying to access CSV files.
• We compared the behavior of the built-in CSVSample.jmx script with our custom script.

The CSVSample.jmx script, pre-packaged with JMeter, operates directly on the agent machine without requiring an explicit file path. This contrasts with the custom script, which relied on an absolute path to the CSV file. The agent machine's lack of read access to the remote directory prevented the custom script from locating and processing the CSV data.

Conclusion:

The issue was caused by the custom script's reliance on an absolute path to the CSV file. Since the agent machine lacked read access to the remote directory, it couldn't locate the file, leading to the exception. This highlights the importance of considering file paths and permissions when working with CSV files in JMeter tests.