What does the file in "16386" /var/newdb/base/ actually do?

Hi all,

Just a quick question before I use the technical support for this one, hopefully somebody knows and can help me with this.
We have been notified by our firewall, which is a Sophos XGS6500, that it's report disk is almost full.

We check this every month, and on 29th of February we had 45% available (disk size 55% in use)
21 days later, it is on 10% available (Disk size 90% in use)

After logging into the Advanced Shell, and running " du -hs * " we found out that the folder "newdb" was 250GB.
After snooping around in this folder, we found the file "16386" to be 249GB large.

I tried searching on the forums, but the only thing I could find was the fact that this file can become very large due to reporting, and theres 2 ways to make it smaller
1. Flush reports with "Manual Purge" (This is the option we have used today and it has significantly decreased)
2. Flush reports with CLI, this requires a reboot and we do not want this.

Maybe somebody here can help us with knowing what this DB file does, and how we could check why it has increased so fast in 21 days.
Would love to hear something!