Added pprof tool

[d-ulyanov]

Added standard GO pprof tool to Telegraf. This tool is useful for developers: from time to time we need to understand, which plugin or subsystem of Telegraf consumes too much resources.

By default, pprof is disabled.
To enable pprof run Telegraf with pprofaddr parameter:
telegraf --config etc/telegraf.conf --pprofaddr localhost:6060

[sparrc]

thanks for adding this, can you add it to the --help doc? also put in the doc the format of the address, (ie, localhost:6060)

I would also call the flag --pprof-addr (with a dash)

[d-ulyanov]

@sparrc I've just added pprof-addr to help with example and renamed pprofaddr to pprof-addr - I agree, it seems better.

Reason why we've added pprof - high CPU consumption by Telegraf: up to 20% of total CPU on modern servers.
It was caused by built-in NETSTAT plugin - it makes too much system calls inside github.com/shirou/gopsutil to calculate network statistics. Please, consider replacement of this plugin.
As temporary solution - we've replaced netstat plugin by this: https://github.com/monitoring-tools/telegraf-plugins/tree/master/netstat

[d-ulyanov]

@sparrc please, run CI tests again: https://circleci.com/gh/influxdata/telegraf/6260 - its timed out

[d-ulyanov]

@sparrc Let's include this into 1.3.0?

[danielnelson]

Lets update the log message and add this to the CHANGELOG and we should be good to go.

[danielnelson]

I think we have all the information we need to print the full url to this page, let have it write something like:
I! Starting pprof HTTP server at http://localhost:6060/debug/pprof This way I can click on it or copy paste it more easily.

[d-ulyanov]

@danielnelson, thanks for review. Changes done.

Could you also move forward our contributions:
#2387
#2594

We hope to see them in 1.3 too

[danielnelson]

Can you rebase?

[danielnelson]

Nevermind, It's merged!