Start Sampling after a certain Threshold

[eltalkarim]

In reference to a Gitter discussion with @joe-elliott and this #425

Requirement - what kind of business use case are you trying to solve?

if an operation does not occur much and its a child of subsequent operations that are under a probabilistic sampling rate. Jaeger agent does not ensure that it would be represented a least once. (so we can draw the dependency graph).

Problem - what in Jaeger blocks you from solving the requirement?

At least 1 span should be captured from each unique operation to ensure completness if ann operation does not happen much but its a child of another operation that occurs lots. For example operation A (high freq, low sampling rate)=>operation B (low freq, high sampling rate) but it could be that the low sampling rate of operation A will also sample B making it very improbably to catch any operation b spans. In my use case, I am more interested in the completeness that are operated at least represented once. By completness I mean all each unique operation is represented at least once.

Proposal - what do you suggest to solve the problem or improve the existing situation?

In the scope of tail based sampling #425 ,we can make sure that we sample probabliscaly after a certain threshold, aka after catching a certain number of spans. It could be in the sampling config.