[ltowarek]

[SDK] Clamp BatchSpanProcessor max_export_batch_size to max_queue_size

Changes

Since #4466, BatchSpanProcessor waits for a full batch before it exports. If max_export_batch_size is larger than max_queue_size, a full batch never arrives. Spans are then exported only when schedule_delay_millis expires, and new spans are dropped once the queue is full.

The specification says the batch size must be less than or equal to the queue size, so such values are invalid. They still worked before #4466, though. Since #4466, apps that use them lose spans, and nothing points at the configuration as the cause.

The fix is based on the Java and Python SDKs, which both refuse such values. Java clamps the batch size to the queue size and logs a warning (BatchSpanProcessorBuilder). Python raises a ValueError (BatchSpanProcessor). opentelemetry-cpp must also work without exceptions, so this PR does what Java does: it clamps and logs one warning at construction. A max_queue_size of 0 is left alone, because clamping to it would make the worker spin.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.60%. Comparing base (c827b60) to head (5317bc2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4727      +/-   ##
==========================================
- Coverage   86.70%   86.60%   -0.09%     
==========================================
  Files         527      530       +3     
  Lines       20902    21009     +107     
==========================================
+ Hits        18121    18193      +72     
- Misses       2781     2816      +35     

Files with missing lines	Coverage Δ
sdk/src/trace/batch_span_processor.cc	92.35% <100.00%> (+2.47%)	⬆️

... and 2 files with indirect coverage changes

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[lalitb]

LGTM. one comment, can be a follow-up fix.

[ltowarek]

LGTM. one comment, can be a follow-up fix.

Thanks for the review! I'll create a follow-up PR.