Use stderr instead of file

[waghanza]

Hi,

Benchmark results (wrk results) are written in file, and this one is parsed as CSV.

To simplify process, it will be convenient to use stderr (memory) to write this CSV.

Regards,

[waghanza]

This could impact latency metrics. As an example on the same environment, I have (for a concurrency of 1000)

• master

Language (Runtime)	Framework (Middleware)	Average	50% percentile	90% percentile	99% percentile	99.9% percentile	Standard deviation
ruby	roda	2.95 ms	2.04 ms	6.29 ms	15.79 ms	65.76 ms	3219.67
ruby	rack-routing	3.80 ms	2.33 ms	8.53 ms	24.83 ms	113.65 ms	5220.33
ruby	hanami	6.24 ms	2.82 ms	15.89 ms	47.66 ms	144.62 ms	9571.00
ruby	flame	6.65 ms	3.74 ms	16.38 ms	37.75 ms	123.35 ms	8038.67
ruby	sinatra	8.23 ms	4.24 ms	19.48 ms	64.23 ms	185.05 ms	12433.00
ruby	rails	30.17 ms	7.44 ms	96.35 ms	184.99 ms	356.68 ms	44082.33

• here

Language (Runtime)	Framework (Middleware)	Average	50% percentile	90% percentile	99% percentile	99.9% percentile	Standard deviation
ruby	sinatra	9.27 ms	1.93 ms	27.10 ms	85.32 ms	226.08 ms	17126.67
ruby	roda	3.10 ms	2.02 ms	6.51 ms	18.96 ms	128.36 ms	4143.33
ruby	rack-routing	3.79 ms	2.44 ms	8.45 ms	21.99 ms	106.48 ms	4616.67
ruby	hanami	6.31 ms	2.83 ms	16.29 ms	46.90 ms	138.03 ms	9486.00
ruby	flame	7.12 ms	3.66 ms	17.96 ms	43.42 ms	127.91 ms	9103.67
ruby	rails	29.45 ms	7.34 ms	94.01 ms	179.29 ms	340.13 ms	42854.33