Here's an example query I'm generating to Splunk 6.0:
a_t AND host="jcoker-mac.local" AND rootReq | stats values(a_func), values(a_pfuncs), count, sum(a_t), sum(a_self_cpu), sum(a_self_io), avg(a_t), avg(a_self), avg(a_cpu), avg(a_self_cpu), avg(a_io), avg(a_self_io), avg(a_sql), avg(a_self_sql), avg(a_kv), avg(a_self_kv) by t_type, t_action, a_st | sort -sum(a_t), -sum(a_self), -count | rename t_type AS "Type", t_action AS "Action", a_st AS "Status", values(a_func) AS "Function", values(a_pfuncs) AS "Parent Functions", count AS "Calls", sum(a_t) AS "Σ T. time", sum(a_self_cpu) AS "Σ S. CPU", sum(a_self_io) AS "Σ S. I/O", avg(a_t) AS "μ T. time", avg(a_self) AS "μ S. time", avg(a_cpu) AS "μ T. CPU", avg(a_self_cpu) AS "μ S. CPU", avg(a_io) AS "μ T. I/O", avg(a_self_io) AS "μ S. I/O", avg(a_sql) AS "μ T. SQL", avg(a_self_sql) AS "μ S. SQL", avg(a_kv) AS "μ T. K/V", avg(a_self_kv) AS "μ S. K/V"
So, I'm explicitly fetching individual fields, and I don't care about any other fields (nor do I care about extra metadata since that isn't going anywhere).
If you use the
fields command to explicitly state which fields should be extracted, it will override any search mode setting.
When you change the "search mode" in the Splunk UI, ultimately the effect is to send an argument called "adhocsearchlevel" on the POST request that dispatches the search. The value is one of fast/smart/verbose.
"smart" does a little more client-side logic, but the main upshot is that when this argument is present on the dispatch POST, it overrides older arguments called "statusbuckets" and "requiredfield_list", even though frequently those older arguments are also submitted. However the interaction between the three arguments may be more complicated.
Note that if your search possesses a
fields command, it's possible that the fields command contributes some effect as well, but I doubt that the fields command is sufficient to completely counteract everything that might be happening if you're sending the other API args.
Anyway, lets back up a little. For every Splunk search, there's a "streaming portion", which is basically the initial search clause, plus whatever "streaming" commands (eg eval, rename, rex, where, etc) that might come after it, up to and not including the first "transforming command" (eg stats, timechart, chart, transaction, sort). If there is no transforming command then the search is a "purely streaming" search. (Conversely if the search is something like "| inputlookup" then there is no streaming portion and all these args are ignored)
for searches that have a streaming component,
status_buckets is an integer that tells Splunk how many timebuckets it should keep for summary statistics about the extracted fields present in the streaming portion of the results. This last part is weird - status_buckets only concerns the space of fields that exist at the last pipe before the transforming stuff starts.
requiredfieldlist on the other hand tells splunk how many fields in addition to any that might be specified in the search language (eg in a fields command), for which it should keep summary data in its status_buckets.
Example: you have a search over exactly 2 hours of data, and you set statusbuckets to 2, and requiredfieldlist to "username,application". Splunkd notices that application is already mentioned explicitly in the search language so the application in requiredfield_list is ignored. It then proceeds to keep 2 buckets of summary statistics, for all the fields referenced in the search, plus the field "username".
Short version - If you're using the Advanced XML or Sideview Utils in 6.0, or if you're using Splunk 5.X or earlier, the modules are responsible for automatically sorting out what the statusbuckets and requiredfieldlist should be. The Splunk modules do a decent job of this. The Sideview modules from Sideview Utils do perhaps a slightly better job. Either way you don't have to really worry about any of this stuff and the searches dispatched will be as optimized as they can be. If you're ever worried that they're not optimized, just use a tool like Firebug to look at the POST args and you can see for yourself, or you can see statusbuckets in the job dictionary if you inspect the job.
In the new Splunk Web Framework that ships with 6.0, you may want to worry about this. But I would advise you to just make sure that statusbuckets is unset or being set to 0, and requiredfieldlist is left unset, and you'll be fine. You can set `adhocsearchlevel=fast` as well, but on a search where statusbuckets is omitted or 0, and requiredfieldlist is omitted, I really don't think it's going to make any difference.