Qlik Sense engine "Document Load: Long pre-generation time" warning may occur in Engine logs while an app is opening slower than expected.
10934 20210527T075324.538+0200 WARN VMQLIK System.Engine.Engine 185 b61ba19a-61c3-4248-8a4d-74asssc08afa ABC\QLIKSENSEPR Document Load: Long pre-generation time (>100% of open). Review expression dimension usage, and consider moving definitions to the load script. Pre-gen can be disabled at the cost of sheet calculation performance. 35d66cc9-d537-464c-bddc-42f3a9320dfe INTRA-TPG vazeille 20210527T075324.528+0200 6068 2784 e467645c-4f82-4d6e-a7e9-449609139743 6ccaa3ec-b5c2-4e7e-917f-a66f6c44da19 20210526T152424.000+0200 b61ba19a-61c3-4248-8a4d-74aacdc08afa
Environment
- Qlik Sense Enterprise on Windows
Cause
The root cause for this error is that the app has a noticeable amount of dimensions defined as expressions, instead of field references to the data model. By default, these expression-based dimensions will be evaluated during the initial app opening and added as Field-on-the-fly to the data model.
See Qlik Design Blog post below for more details about the Field-on-the-fly concept;
https://community.qlik.com/t5/Qlik-Design-Blog/Calculated-Fields/ba-p/1694383
The pre-generation of Field-on-the-fly is most often not a noticeable part of the initial app opening, but some characteristics of the app may contribute to that the pre-generation takes a longer time;
- Number of expression based dimensions
- The complexity of expression used in dimension
- Data volume related to resolving the Field-on-the-fly
- Low or slow server resource increasing processing time
Resolution
The recommended approach to resolve the "Document Load: Long pre-generation time" warning in the engine log, is to review the related app and transform expression-based dimensions from the visualizations and master items into actual fields in the data model.
Calculated dimensions with logical comparisons can often be resolved into fields by moving the logic.
It is possible to disable the Pre-generation of Fields-on-the-Fly, by adding DisableFotfPreGen=1 in Engine settings.ini:
https://community.qlik.com/t5/Knowledge-Base/How-to-modify-Qlik-Sense-Engine-s-Settings-ini/ta-p/171...)
Notice, the setting applies to all apps opened on the Engine and may give negative run-time performance when users access sheets.
