splunk housekeeping - directories in /opt/splunk/var/tmp/data

I have 23000 (yes 000) directories in /opt/splunk/var/tmp/data I can't find info in docs as to what this is - how best to find out ? each directory has files in such as : part-00000.gz part-00001.gz part-00002.gz part-00003.gz part-00004.gz part-00005.gz