You've hit on a touchy problem with Splunk: figuring out how busy the infrastructure is at any point in time. There are two things to look at.
1) How many users are currently using Splunk.
This is interesting, but only goes so far. Am I "currently using Splunk" if I have a static dashboard on my screen that has finished loading 10 minutes ago, and I'm either staring at it, or have my head turned talking to someone else? martin_mueller's search in his comment is spot on, and will help you answer this question. 1 hour may be too long of a time frame, as I have found 1m or 5m is more useful for determining how busy Splunk is.
2) How many searches are currently being run.
This is a little harder, because searches come and go, sometimes fairly quickly. A couple of ways to see this info. First, concurrent searches by user. Who's exercising Splunk the most?
index=_internal source=*metrics.log group="search_concurrency" NOT "system total"
| timechart span=1m sum(active_hist_searches) as concurrent_searches by user
Interesting patterns emerge per person/group and time of day.
Second, is this ad-hoc or scheduled? Too many concurrent scheduled searches can really bring Splunk to its knees. A lot of scheduled searches may be okay, if they are very short duration (like populating summary indexes or report acceleration).
`set_sos_index` sourcetype=ps
| multikv
| `get_splunk_process_type`
| search type="searches"
| rex field=ARGS "_--user=(?<search_user>.*?)_--"
| rex field=ARGS "--id=(?<sid>.*?)_--"
| rex field=sid "remote_(?<search_head>[^_]*?)_"
| eval is_remote=if(like(sid,"%remote%"),"remote","local")
| eval is_scheduled=if(like(sid,"%scheduler_%"),"scheduled","ad-hoc")
| eval is_realtime=if(like(sid,"%rt_%"),"real-time","historical")
| eval is_subsearch=if(like(sid,"%subsearch_%"),"subsearch","generic")
| eval search_type=is_remote.", ".is_scheduled.", ".is_realtime
| timechart span=1m dc(sid) AS "Search count" by is_scheduled
Props go out to hexx (SoS guru) for these, and hopefully they (or something like it) will show up in SoS in the near future.
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