cmd/pprof: make flamegraph page the starting one in http UI

[ethercrow]

Go version

all

Output of go env in your module/workspace:

Irrelevant

What did you do?

When you do go tool pprof -http 127.0.0.1:6611 my_binary my_profile.pbgz

What did you see happen?

Your browser shows you this:

so that you have to go the address bar and type /flamegraph at the end to see the profile.

Or if you jump through the hoops of installing graphviz, first you see a page with a graph that you don't understand. At least I have never met a person who really understands it. And pretty much every talk on go pprof that I've seen includes a statement like "just ignore this and switch to the flamegraph view".

What did you expect to see?

So why not make the flamegraph view default?

[ALTree]

Agree that serving the graph page by default may not be optimal, especially considering that is the only page that will be unavailable if an external command (dot) is not installed. The flamegraph (or maybe the textual representation at /top) would be a better default.

[ALTree]

(It's kinda unfortunate that the graph is served directly at /ui, while the other stuff is at subpages like /ui/top. We could also serve the graph at ui/graph -to uniform things- and then serve the default at /ui)

[mknyszek]

Since the Go distribution just vendors https://github.com/google/pprof, correct me if I'm wrong but I think this is more an improvement for https://github.com/google/pprof. AFAICT, the decision on what to serve at '/' is made by the pprof tool internals, not the Go distribution's wrapper. Once a change is made upstream, we can re-vendor it.

[mknyszek]

Ah, sorry... 😅 I also meant to say that this should probably be filed as a feature request at https://github.com/google/pprof/issues. I can +1 the issue since it does seem like a fairly poor user experience to pop open the web UI and immediately be told something doesn't work. That might help move things along. But as a general matter of course such issues should be put in front of the actual owners of the code.

[ethercrow]

No problem, I moved the issue to the pprof repository, thanks for the pointer.

[dmitshur]

This change happened upstream, and this is now done for cmd/pprof via CL 725500. (CC @prattmic.) Added this issue to the Go1.26 milestone.