Does Zipkin support ratelimiting sampling

[xihw]

Besides percentage rate, I found jaeger also supports other sampling strategies like "ratelimiting" in which we can specify how many traces to be sampled per second. (https://www.jaegertracing.io/docs/sampling/), does Zipkin support this ?

[codefromthecrypt]

we don't currently pack-in a "rate limited" sampler. I've made notes in the past about reservoir sampling which is another way of saying similar. For example, you can have up to 100 traces per second and then a percentage after that. spring-cloud/spring-cloud-sleuth#92 (comment) The implementation is not difficult, it would be implementing brave's Sampler type similar to how x-ray does it https://github.com/aws/aws-xray-sdk-java/blob/master/aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/strategy/sampling/Reservoir.java it could get more complicated, though, for example adaptive etc.. however basic rate is not difficult even if it is likely less efficient than counting (due to needing to read the current time). If this issue gets a lot of votes (likely) we can implement it. Meanwhile you could consider implementing on your own and possibly raising a pull request.

[devinsba]

@adriancole mind if I rename this issue to something along the lines of:

Feature Request: Reservoir Sampler

I need this in zipkin-aws and it definitely belongs in brave other than the XRay specific config

[codefromthecrypt]

sure I know there was some naming discussion going on in census where at least one person didn't like the term reservoir. but anyway yep go ahead!

[codefromthecrypt]

This part is implemented.. compositions can be done in a different issue