Add ability to disable compression in PrometheusScrapeHandler

[Myllyenko]

In our setup, metrics are being pulled from PrometheusScrapeHandler by an agent process running on the same machine. In this case, response compression is meaningless (because there is no bottleneck in network throughput) and even harmful, because according to our profiling, compression takes about 60% of response generation time (or 10—20 seconds in absolute values). We've tried a patched version of the handler with compression removed and it really improved overall performance of the metrics pipeline.

Currently, PrometheusScrapeHandler automatically enables compression if an incoming request contains corresponding Accept-Encoding value. We'd like to be able to disable compression via configuration of PrometheusScrapeHandler

[zeitlinger]

Why not use Accept-Encoding to prevent compression?

[Myllyenko]

Why not use Accept-Encoding to prevent compression?

Our agent process is designed for a common use case, and thus it sets Accept-Encoding: gzip in its requests. As far as I understand, this header just tells the server that the client supports compression, but does not force it to compress the data. So, the final decision on response encoding is for the server to make.

[zeitlinger]

So, the final decision on response encoding is for the server to make.

Right, that makes sense

Accept-PR: true 😄