topic What is the difference between fieldformat and eval operation time conversion? in Splunk Search

What is the difference between fieldformat and eval operation time conversion?

splunkn — Tue, 12 Jul 2016 07:33:10 GMT

I am able to see that the following search returns the same result for fieldformat as well as eval time conversion operation. Is there any significant difference between these two in performance wise or in any others?

index=_internal | head 1 | eval abc="1468308151" | fieldformat mytime=strftime(abc,"%H:%M") | eval mytime1=strftime(abc,"%H:%M") | table abc mytime mytime1

index=_internal | head 1 | eval abc="1468308151" | fieldformat mytime=strftime(abc,"%c") | eval mytime1=strftime(abc,"%c") | table abc mytime mytime1

Here mytime and mytime1 fetch the same results. as "12:51"

Thanks

Re: What is the difference between fieldformat and eval operation time conversion?

javiergn — Tue, 12 Jul 2016 07:45:21 GMT

Fieldformat

With the fieldformat command you can
use eval expressions to change the
format of a field value when the
results render. You can change the
format without changing the underlying
value of the field.

Eval

Eval will change the underlying value of the field.

Re: What is the difference between fieldformat and eval operation time conversion?

splunkn — Tue, 12 Jul 2016 08:28:59 GMT

thanks javiergn..so coming to this scenario, formattting my epoch time here going to work same right? no better performance over one another?

Re: What is the difference between fieldformat and eval operation time conversion?

kishorksudha — Tue, 12 Jul 2016 08:34:12 GMT

fieldformat is good for viewing purpose, when you want to do some calculations on the underlying field you need to use eval and work out.

Basically

With FieldFormat you cant use the modified format to do calculations
With eval you can use the modified values to do calculations

Re: What is the difference between fieldformat and eval operation time conversion?

javiergn — Tue, 12 Jul 2016 08:42:42 GMT

If there was any performance difference it would be tiny in any case but I couldn't say without running thorough tests.

What you need to keep in mind is whether you want your field value to change or not. If you want to keep the value as it is but just display it differently (user-friendly for instance), then use fieldformat. Otherwise eval can do.

Re: What is the difference between fieldformat and eval operation time conversion?

woodcock — Tue, 12 Jul 2016 12:34:15 GMT

Using fieldformat creates an alias for a field leaving the original field value completely unchanged, whereas using eval updates (completely destroys) the original field value and replaces it with a new value. There should be no difference in performance in either case.