SOLR-1951, the behavior of commons-fileupload in handling multipart form posts came into question. commons-fileupload creates a temporary file for the main content area of such posts, and purportedly has a background thread which cleans up these files. However, Mark Miller discovered that the javadoc in this matter may be incorrect, and that commons-fileupload may in fact just be adding files to the JVM's list of files needing cleanup on exit.
If so, this will show up in two ways: first, temporary files will accumulate in the java.io.tmpdir area. Second, non-heap memory for the JVM will slowly increase over time (since the file pointers the JVM tracks in this way are not kept in the java heap).
I will attach a potential fix; however, this ticket should be viewed as a workitem for the need for further research in this area.