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Flush export queue when it reaches max_export_batch_size #1521

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Feb 12, 2021
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Flush export queue when it reaches max_export_batch_size #1521

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Flush export queue when it reaches `max_export_batch_size`
anton-ryzhov Jan 11, 2021
f1ac8a9
Merge branch 'main' into export-earlier
Feb 11, 2021
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3 changes: 2 additions & 1 deletion CHANGELOG.md
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Expand Up @@ -26,10 +26,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
- Add urllib to opentelemetry-bootstrap target list
([#1584])(https://github.com/open-telemetry/opentelemetry-python/pull/1584)


### Changed
- Read-only Span attributes have been moved to ReadableSpan class
([#1560](https://github.com/open-telemetry/opentelemetry-python/pull/1560))
- `BatchExportSpanProcessor` flushes export queue when it reaches `max_export_batch_size`
([#1521])(https://github.com/open-telemetry/opentelemetry-python/pull/1521)

### Removed
- Remove Configuration
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2 changes: 1 addition & 1 deletion opentelemetry-sdk/src/opentelemetry/sdk/trace/export/__init__.py
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Expand Up @@ -200,7 +200,7 @@ def on_end(self, span: ReadableSpan) -> None:

self.queue.appendleft(span)

if len(self.queue) >= self.max_queue_size // 2:
if len(self.queue) >= self.max_export_batch_size:
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Thanks for the change! I would wonder if it would be better to modify the exporter to flush the queue at something less than the max batch size?

I think this code was written to notify a flush well before the queue filled to handle race conditions. I haven't looked at the code super closely recently, but IIRC there is a possibility for multiple spans to end at the same time, and as a result:

  • first span would notify the flush
  • second span would be dropped, since the flush is notified, but the export_batch_size has been reached.

So maybe take something a little more cautious, like filling up to 80%, and have be the condition for both the notify and the flush itself (refactoring both to a single function call would prevent future splitting of the code).

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Queue overflow and spans drop — that's exactly the issue I'm addressing here.

There are 2 different numbers — max_queue_size = 2048 and max_export_batch_size = 512.

Don't think it's a good idea to flush half- (or 80%-) full requests. That will only make effective_export_batch_size = 0.8 * max_export_batch_size.

Second span in your example won't be dropped if max_queue_size > max_export_batch_size, which should be true.

Maybe as extra check the code should validate that max_queue_size > 2 * max_export_batch_size or so.

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Got it! Makes sense. Sorry about that, I misread the code the first time.

I think the checks there are there are already good (albeit maybe require more documentation).

with self.condition:
self.condition.notify()

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