Occasionally people ask for help in identifying a rogue data input that is suddenly spewing events. If it’s hidden in a ton of similar data it can be difficult to sort out which one is actually the problem. One place to look is the Splunk internal metrics.log. You can find it by searching the internal index (add “index=_internal” to your search) or just look in the file itself (located in $SPLUNK_HOME/var/log/splunk.)

Before I get into what can be found there, I need to explain what metrics.log is not. It is a sampling over 30 second intervals, so it will not give you an exact accounting of all your inputs. For each type of item reported, you get the top ten hot sources over the interval, based on the size of the event (_raw.) It is different from the numbers reported by LicenseManager, which include the indexed fields. Also, the default configuration only maintains the metrics data in the internal index a few days, but by going to the files you can see trends over a period of months if your rolled files go that far back.

A typical metrics.log has stuff like this: