This PR adds counter metrics for the CPU system and the Geth process.
Currently the only metrics available for these items are gauges. Gauges are
fine when the consumer scrapes metrics data at the same interval as Geth
produces new values (every 3 seconds), but it is likely that most consumers
will not scrape that often. Intervals of 10, 15, or maybe even 30 seconds
are probably more common.
So the problem is, how does the consumer estimate what the CPU was doing in
between scrapes. With a counter, it's easy ... you just subtract two
successive values and divide by the time to get a nice, accurate average.
But with a gauge, you can't do that. A gauge reading is an instantaneous
picture of what was happening at that moment, but it gives you no idea
about what was going on between scrapes. Taking an average of values is
meaningless.
* remove uneeded convertion type
* remove redundant type in composite literal
* omit explicit type where implicit
* remove unused redundant parenthesis
* remove redundant import alias duktape
Exposing /debug/metrics and /debug/metrics/prometheus was dependent
on --pprof, which also exposes other HTTP APIs. This change makes it possible
to run the metrics server on an independent endpoint without enabling pprof.
* metrics/prometheus: added prometheus http server and metrics collector
* metrics/prometheus: minor cleanups
* metrics/prometheus: named keys instead name in tag
* metrics/prometheus: minor typo cleanups, sorted report
* metrics: expvar support for ResettingTimer
* metrics: use integers for percentiles; remove Overall
* metrics: fix edge-case panic for index-out-of-range
