We've been using Sharepoint 2013. My question / problem is : The database is about 35 Gb and a shrink db on an SQL level didnt help. How to clear WSS_UsageApplication content?
You can reduce the retention period How-to...
in my case it was 900GB with around 30 big dbo.TaskUsage_PartitionXX tables.
1- go to SSMS and by opening object Explorer (f7) of WSS_UsageApplication find the big tables which in most cases are TaskUsages
2- create a series of truncate and run them
truncate TABLE [dbo].TaskUsage_PartitionXX
3- shrink your whole database to forexample 5% free space which takes around 4 minutes in my case for 900GB
DBCC SHRINKDATABASE(N'WSS_UsageApplication', 5 )
have you looked at http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?ID=400: this link tells you how to set retention which will have a longer lasting effect and help you Shrink your DB (I was able to reclaim nearly 80% of the space consumed by WSS_UsageApplication