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feat(sdk-trace-base): add diagnostic logging when spans are dropped #3610

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merged 3 commits into from
Feb 22, 2023
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feat(sdk-trace-base): add diagnostic logging when spans are dropped #3610

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ddb2cf7
feat(sdk-trace-base): add diagnostic logging when spans are dropped
neoeinstein Feb 13, 2023
f2974ba
test(sdk-trace-base): add test for diagnostic logging on dropped spans
neoeinstein Feb 14, 2023
008255b
Merge remote-tracking branch 'origin/main' into dropped-span-reporting
neoeinstein Feb 14, 2023
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ For experimental package changes, see the [experimental CHANGELOG](experimental/
* feat(sdk-metrics): apply binary search in histogram recording [#3539](https://github.com/open-telemetry/opentelemetry-js/pull/3539) @legendecas
* perf(propagator-jaeger): improve deserializeSpanContext performance [#3541](https://github.com/open-telemetry/opentelemetry-js/pull/3541) @doochik
* feat: support TraceState in SamplingResult [#3530](https://github.com/open-telemetry/opentelemetry-js/pull/3530) @raphael-theriault-swi
* feat(sdk-trace-base): add diagnostic logging when spans are dropped [#3610](https://github.com/open-telemetry/opentelemetry-js/pull/3610) @neoeinstein

### :bug: (Bug Fix)

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16 changes: 16 additions & 0 deletions packages/opentelemetry-sdk-trace-base/src/export/BatchSpanProcessorBase.ts
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Expand Up @@ -44,6 +44,7 @@ export abstract class BatchSpanProcessorBase<T extends BufferConfig>
private _finishedSpans: ReadableSpan[] = [];
private _timer: NodeJS.Timeout | undefined;
private _shutdownOnce: BindOnceFuture<void>;
private _droppedSpansCount: number = 0;

constructor(private readonly _exporter: SpanExporter, config?: T) {
const env = getEnv();
Expand Down Expand Up @@ -117,8 +118,23 @@ export abstract class BatchSpanProcessorBase<T extends BufferConfig>
private _addToBuffer(span: ReadableSpan) {
if (this._finishedSpans.length >= this._maxQueueSize) {
// limit reached, drop span

if (this._droppedSpansCount === 0) {
diag.debug('maxQueueSize reached, dropping spans');
}
this._droppedSpansCount++;
Comment on lines +122 to +125
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This will be very chatty in a system overloaded enough to be dropping spans. Do you think it's needed when the warn log on line 132 is already doing this job?

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For a given stretch of dropped spans, this message will only be reported once, just like the summary warning, so should have the same cardinality as that one. This debug diagnostic can be used to identify at what time those drops started. It's recorded as debug, which should be able to be filtered out if debug diagnostics aren't interesting or desired.

I found it useful as there are two knobs that can be adjusted to prevent dropping spans: queue size and the export interval. The warning message makes it easier to adjust the queue size, but the debug message can make it apparent how often one should be exporting if they don't want to carry a larger memory load associated with a larger queue.

I'm not particularly attached to this message, so if we want it removed, that's fine with me.


return;
}

if (this._droppedSpansCount > 0) {
// some spans were dropped, log once with count of spans dropped
diag.warn(
`Dropped ${this._droppedSpansCount} spans because maxQueueSize reached`
);
this._droppedSpansCount = 0;
}

this._finishedSpans.push(span);
this._maybeStartTimer();
}
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34 changes: 34 additions & 0 deletions packages/opentelemetry-sdk-trace-base/test/common/export/BatchSpanProcessorBase.test.ts
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Expand Up @@ -462,6 +462,40 @@ describe('BatchSpanProcessorBase', () => {
}
assert.equal(processor['_finishedSpans'].length, 6);
});
it('should count and report dropped spans', done => {
const debugStub = sinon.spy(diag, 'debug');
const warnStub = sinon.spy(diag, 'warn');
const span = createSampledSpan('test');
for (let i = 0, j = 6; i < j; i++) {
processor.onStart(span, ROOT_CONTEXT);
processor.onEnd(span);
}
assert.equal(processor['_finishedSpans'].length, 6);
assert.equal(processor['_droppedSpansCount'], 0);
sinon.assert.notCalled(debugStub);

processor.onStart(span, ROOT_CONTEXT);
processor.onEnd(span);

assert.equal(processor['_finishedSpans'].length, 6);
assert.equal(processor['_droppedSpansCount'], 1);
sinon.assert.calledOnce(debugStub);

processor.forceFlush().then(() => {
processor.onStart(span, ROOT_CONTEXT);
processor.onEnd(span);

assert.equal(processor['_finishedSpans'].length, 1);
assert.equal(processor['_droppedSpansCount'], 0);

sinon.assert.calledOnceWithExactly(
warnStub,
'Dropped 1 spans because maxQueueSize reached'
);

done();
});
});
});
});

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