Traffic logging for the Engine, which is turned off by default, can be useful in a few diagnostic situations. Traffic logging logs the JSON traffic exchanged in the WebSocket connection between the Engine and any client into a text file. This logging level is extremely verbose and should be used with caution and only in circumstances where there is an explicit need for its information. The main performance bottleneck when turning on this logging level is CPU consumption needed to capture and write the verbose traffic between the Engine and client.
In a testing scenario with 200 concurrent users accessing a basic application, the performance impact can be seen as follows:
RAM consumption is as follows:
The RAM impact of Traffic logging is minimal whereas there is a ~23% increase in CPU utilization with traffic logging enabled.
Disable Traffic logging unless there is an explicit, short-term need. The performance degradation due to having it on is substantial enough to justify never running it unless otherwise needed.
To check the Traffic logging level:
- Go into the QMC
- Navigate to the Engines section of the QMC
- Edit an/the Engine
- Navigate to the Logging section
- Inspect the Traffic log level
- If logging is set to any value but Off, change it to Off
- You will need to restart both the Qlik Sense Engine Service and the Qlik Sense Service Dispatcher for this change to take effect
- Repeat on all Engine nodes as applicable