Tracing overview

Every message's trace lifecycle consists of several stages:

1. Sampling. Before actual trace is created, message needs to be successfully sampled. Such mechanism allows setup tracing extension to sample only some part of messages to reduce overhead when used in production environment.
2. Annotating. Any (created) trace can be annotated by basic and binary annotations. Basic annotations contain timestamp and description and can be displayed in timeline. Binary annotations are key-value pairs attached to trace itself.
3. Submitting. After some message was explicitly marked as response to traced message, corresponding trace is sent to (external) collector service. If response remains unspecified, trace is sent anyway after some timeout. Any annotations written to already submitted trace are ignored.