What to do if rebuilding the cache of a datasource takes very long?

If the App is very big and/or has many sheets and objects, it is highly recomended to use the Set Filter Before Rebuilding Cache option together with a Filter Field Name and Filter Value to reduce the time when rebuilding the cache.

Issue

Resolution

Use the Set Filter Before Rebuilding Cache option together with a Filter Field Name and Filter Value to reduce the time when rebuilding the cache.

What is the Cache?

It is a dictonary of all the fields, variables and id of objects in the App. It is only metadata.

What does it mean Rebuild the Cache?

It is the process of creating this dictonary of metadata.

When is it necessary to Rebuild the Cache?

When new objects, fields or variables were added to the App and M&D needs these new elements in a report and/or task.

Why Rebuilding the Cache can take very long?

M&D will request Qlik Sense to open the App and it will visit every sheet gathering all the object id's present in the sheet. Qlik Sense will load the App into memory and it will do all the necessary calculations to render all the charts and tables present in the sheet, and for every sheet. If it is a very big app with many sheets and objects, the process can take long.

How to minimize the time to Rebuild the Cache?

Use the option Set Filter Before Rebuilding Cache together with a Filter Field Name and Filter Value to set a filter that will load as few rows as possible, making the process of creating the dictionary/rebuilding the cache much faster. 

When setting the option Set Filter Before Rebuilding Cache, is the dataset reduced when distributing Reports? 

No, the dataset is only reduced when rebuilding the cache/creating the dictionary. It is not reduced when distributing reports.

How to Rebuild the Cache?

Press the sync icon on the list of Datasources.