varnishtop feature request: show _expensive_ urls

[Harm Verhagen]

Hi,

I was looking into varnishtop to find performance bottlenecks on a website.
Thinking about it I think a useful feature  is currently missing from this
tool. (while it _has_ all the available raw data).
I'd like to discuss it here, to get your opinion.

Currently varnishtop shows the top urls purely based on frequency. Depending
on your usecase that might be usefull, but might also NOT give you the
bottlenecks you are looking for.


I'd like to use varnish for the following (example) scenario:

Consider an website site with many dynamic urls.   (dynamic means varnish
does not cache them, they are always passed through to the backend)
Of those there are two urls that are behaving  "badly"  X and Y  (that is
they are  slow: lets say 400ms)
We don't know that _these_ to are behaving badly.

X:  is called very low frequently   -> so this is NOT a perf bottleneck.
Y: is called often  ->  THIS IS THE BOTTLENECK  -> this is the url that
brings down the site.
Z:  is called often -> this one is fast -> not a bottleneck.

I'd like varnishtop  to show Y, (and not X-like urls( urls that are not
called often), and not Z-like urls (urls that are fast).

For this to work varnishtop should (optionally ofcourse) order the url not
by request/rate, but rather by  "total time spend" on this url. Something
like the product of freq and avg time on an url.

in this case
expensive url !=  often called backend url
expensive url !=  slow backend url
expensive url  =   backend url with high  total time spend  (freq x
duration)    (So the slow ones, that are called often)


What do you guys think ?
This would instantly give the problem areas of a website, no ?


Regards,
Harm Verhagen
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