Create new trace if multiple non-childof refs from different traces

[objectiser]

Signed-off-by: Gary Brown gary@brownuk.com

Which problem is this PR solving?

If a span is created with multiple "FOLLOWS_FROM" references from different traces, the new span is created as a child of the first supplied reference. As discussed on the bi-weekly call 18th Oct, this situation should result in a new trace being created.

Short description of the changes

If more than one reference is supplied, with no CHILD_OF type, then check whether they belong to the same trace instance. If not, then treat as a root span of a new trace.

[codecov]

Codecov Report

Merging #665 into master will decrease coverage by 0.24%.
The diff coverage is 96.29%.

@@             Coverage Diff              @@
##             master     #665      +/-   ##
============================================
- Coverage     89.93%   89.68%   -0.25%     
- Complexity      569      570       +1     
============================================
  Files            69       69              
  Lines          2086     2104      +18     
  Branches        266      273       +7     
============================================
+ Hits           1876     1887      +11     
- Misses          129      135       +6     
- Partials         81       82       +1

Impacted Files	Coverage Δ	Complexity Δ
.../src/main/java/io/jaegertracing/Configuration.java	93.3% <100%> (+0.12%)	46 <1> (+2)	⬆️
...n/java/io/jaegertracing/internal/JaegerTracer.java	89.4% <95.45%> (+0.47%)	27 <1> (+1)	⬆️
...rtracing/internal/reporters/CompositeReporter.java	71.42% <0%> (-28.58%)	6% <0%> (-1%)
...gertracing/internal/reporters/LoggingReporter.java	81.81% <0%> (-9.1%)	4% <0%> (-1%)
...egertracing/internal/reporters/RemoteReporter.java	87.35% <0%> (-2.3%)	7% <0%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 46798bd...961d146. Read the comment docs.

[yurishkuro]

I think this needs a config option to enable new behavior, as it's not backwards compatible.

[objectiser]

@yurishkuro Unless we consider the current behaviour a bug :)

There are no unit tests that clearly define what behaviour is expected in such situations - and currently there is no way to create such a root span with references to multiple other traces, which to me is a limitation/bug?

[yurishkuro]

I don't think it's a bug. It's pretty consistent across clients and fairly reasonable - first reference becomes the parent.

The reason why a root span cannot be created is not because it's a big, but because the OT is missing a start option for that, leaving the behavior up to the tracer.

I find using first ref as parent to be more intuitive behavior than flipping to root if refs are for different traces, and it's already the current behavior, so a config option is a cleaner way imo.

Btw we should open a tracking issue in the main repo if we want to make this change across all clients.