twitter/finagle

Let's support non-RPC spans

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#541 opened on Aug 9, 2016

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 (10 comments) (2 reactions) (0 assignees)Scala (8,864 stars) (1,435 forks)batch import
help wanted

Description

The current tracing system is special-cased for client and server spans. There are non-rpc spans, such as expensive local code or messaging activity that are not currently representable in finagle. Let's make them possible!

Expected behavior

I'd like to be able to indicate the start and finish of an abstract operation, without relying on annotation values. For example:

Trace.recordStart() -> Tracer.record(Annotation.Start())
Trace.recordOperation(message: operation) -> Tracer.record(Annotation.Operation(operation))
Trace.recordFinish() -> Tracer.record(Annotation.Finish())
Trace.recordError(message: String) -> Tracer.record(Annotation.Error(message))

These annotations control the authoritative start and finish (success or error) of an abstract span. Annotation.Operation is the same use as Annotation.Rpc, except it more clearly indicates it isn't necessarily an RPC (ex a one-way message).

Actual behavior

Right now, you can only authoritatively create and finish RPC spans. If you create a different type of span, you end up with a "finagle.flush" annotation 2 minutes later as the tracer has no idea that the span is complete. It is also impossible to create a span that only includes binary annotations.

Contributor guide

Tech stack
scala
Domain
observability
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic understanding of ScalaFamiliarity with Finagle's tracing systemKnowledge of distributed tracing concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
The goal is to add support for non RPC spans in Finagle's tracing system. Start by examining the existing Tracing and Tracer classes to understand how RPC spans are currently created and finished. Look at the Annotation and Span data structures to see where new annotations like Start, Finish, Operation, and Error could be added. Review any discussions or linked resources in the issue comments (though none are linked). Consider implementing the suggested API that uses recordStart, recordOperation, etc. Ensure that the new annotations correctly control span lifecycle without relying on finagle.flush. Test with a simple example where a non RPC span is created and verify that the span is properly completed.