replace regex to escape special chars with simple binary comprehension

[RoadRunnr]

Running regex (especially three times in a row) is much more expensive
that a binary comprehension. This makes little difference for small
data sets, for anything beyond a few hundred items it becomes measurable.
Data sets beyond a few thousand items are completely unusable without
this change.

[deadtrickster]

Hi, thank you for the PRs. Do you have benchmark code at hand? It's ok if these are the follow ups for real world observations, no problem. I want to have something scraping-related in the benchmarks folder for some time already.

[deadtrickster]

I also wonder if it makes sense to do just file:write instead of constructing binary and then doing write. OTOH escaped labels/help strings could be just cached on first encounter.

[RoadRunnr]

Hi, thank you for the PRs. Do you have benchmark code at hand? It's ok if these are the follow ups for real world observations, no problem. I want to have something scraping-related in the benchmarks folder for some time already.

I don't have a real benchmark, just a few lines that create a configurable amount of metrics and then I try to read them. For this PR I read them through a cowboy handler, for #120 is use timer:tc, e.g.:

Callback = fun (Registry, Collector) -> {Time, _} = timer:tc(fun() -> prometheus_collector:collect_mf(Registry, Collector, fun({T, _}) -> io:format("T: ~p~n", [T]), ok; (_) -> ok end) end), io:format("~p, ~p, ~p~n", [Time, Registry, Collector]) end.
timer:tc(fun() -> prometheus_registry:collect(default, Callback) end). 

[deadtrickster]

Hey, maybe you can share those lines too? it's totally possible to timer:tc the format call.

[RoadRunnr]

I have pushed the bits and pieces that I used into RoadRunnr/prom

[deadtrickster]

thanks, I will play a bit and this will be merged soon.

[RoadRunnr]

I have two further speed ups in this branch https://github.com/RoadRunnr/prometheus.erl/commits/experimental/speedup.

For 200k histograms with 10 data points each, I get a ~60% speedup in the text formatting on top of the other improvements (from ~13 sec down to ~5 sec).

Shall I open a new PR with the combined changes or wait till you have merge this PR and #120 ?

[deadtrickster]

I think having "replace io_lib:format with faster helpers" commit in this MR makes sense.