On a large system, bulk imports slow file garbage collection to a crawl. The total number of files to be deleted was about 14 million. Initially, it would run quickly, but then slow down, to the point where only a few files would be deleted every few minutes. The jvm was only using 50% of the CPU (and therefore, probably not GC thrashing). JStacks showed the collector scanning the metadata table to remove referenced files from the delete list.
If the bulk ingest requests were stopped, the GC completed quickly.