Smart search is the global search tool in Qlik Sense, enabling you to search the entire data set in your app from any sheet in the app. See Using Smart Searchon the official Qlik Online Help for details.
This search is indexed to disk at %Share%/Apps/Search.
As time goes on, the index grows and commits more disk space.
The contents of the Qlik Sense Search folders can be deleted to free up disk space. The content pertains to App ID's, so it would be best to remove those which are not often used. The only effect this would have is increasing the amount of time needed to complete a Smart Search for this same App in the future.
Qlik Sense can also be configured to purge the Search Folder on a schedule. The setting will need to be applied in the settings.ini of either the Qlik Sense Enterprise Server or the Qlik Sense Desktop. For information on how to edit the settings.ini file, reference How to modify Qlik Sense Engine's Settings.ini.
Qlik Sense Server
Qlik Sense Desktop
-1 the search index folder is never purged.
0 or negative (except -1), the purge happens constantly.
strictly positive value, the search index folder is purged each ServerPurgeSearchIndexFileInterval seconds.
The purge system removes the unused search index files. In addition, it removes the oldest used search index files until the search index folder is smaller than ServerSearchIndexFileDirectoryMaximumSizeInMBytes.
Maximum size of the search index directory in megabytes. During the periodic purge, old indexes are removed until the total size of index files is below this threshold. If negative, do not limit the size of the directory.
Make sure to add both parameters mentioned above into the settings.ini, the cleaning will happen at the specified intervall but only after the size limit is reached.