Skip to content

Add rate‑limited log warning when BatchSpanProcessor drops spans #8167

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
VamshikrishnaMonagari wants to merge 5 commits into
base: main
Choose a base branch
from
+47 −0
Open

Add rate‑limited log warning when BatchSpanProcessor drops spans #8167

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
ff11a8b
Alert through logs for dropped spans in BatchSpanProcessor
VamshikrishnaMonagari Mar 9, 2026
912e997
Fix variable name for throttling logger in BatchSpanProcessor
VamshikrishnaMonagari Mar 11, 2026
d14a2cc
Replace ThrottlingLogger with per-batch drop count logging in BatchSp…
VamshikrishnaMonagari Mar 18, 2026
ad025e3
Address test review feedback: use forceFlush and assert full message
VamshikrishnaMonagari Mar 22, 2026
903425f
Fix checkstyle import ordering in BatchSpanProcessorTest
VamshikrishnaMonagari Mar 24, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
14 changes: 14 additions & 0 deletions sdk/trace/src/main/java/io/opentelemetry/sdk/trace/export/BatchSpanProcessor.java
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -184,6 +184,7 @@ private static final class Worker implements Runnable {
private volatile boolean continueWork = true;
private final ArrayList<SpanData> batch;
private final long maxQueueSize;
private final AtomicInteger droppedSpanCount = new AtomicInteger(0);

private Worker(
SpanExporter spanExporter,
Expand Down Expand Up @@ -212,6 +213,7 @@ private void addSpan(ReadableSpan span) {
spanProcessorInstrumentation.buildQueueMetricsOnce(maxQueueSize, queue::size);
if (!queue.offer(span)) {
spanProcessorInstrumentation.dropSpans(1);
droppedSpanCount.incrementAndGet();
Copy link
Contributor

@jkwatson jkwatson Mar 18, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

@jack-berg do you think it would make sense to add something to the SpanProcessorInstrumentation to get this information, rather than tracking it separately here?
/cc @anuraaga

Copy link
Member

@jack-berg jack-berg Mar 19, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Would have to maintain state over there but at least it would be hidden behind a central abstraction

An otel maximalist answer here would be:

  • Record the log using the otel log API (first solving Sketch out slf4j bridge #7905)
  • Rely on temporal correlation between logs and metrics for the user to look up the metric state at the time the log was observed

I'm not trying to boil the ocean for this though 😛

Copy link
Contributor

@anuraaga anuraaga Mar 19, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Yeah if the SpanProcessorInstrumentation was already using an async counter or such with tracking, just reading that would be fine. But it's probably better to keep that synchronous (I think?) so keeping this BSP implementation detail in BSP seems to make more sense

} else {
if (queueSize.incrementAndGet() >= spansNeeded.get()) {
signal.offer(true);
Expand Down Expand Up @@ -315,6 +317,18 @@ private void exportCurrentBatch() {
return;
}

int dropped = droppedSpanCount.getAndSet(0);
if (dropped > 0) {
logger.log(
Level.WARNING,
"BatchSpanProcessor dropped "
+ dropped
+ " span(s) since the last export because the queue is full"
+ " (maxQueueSize="
+ maxQueueSize
+ ")");
}

String error = null;
try {
CompletableResultCode result = spanExporter.export(Collections.unmodifiableList(batch));
Expand Down
33 changes: 33 additions & 0 deletions sdk/trace/src/test/java/io/opentelemetry/sdk/trace/export/BatchSpanProcessorTest.java
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

import io.github.netmikey.logunit.api.LogCapturer;
import io.opentelemetry.api.internal.GuardedBy;
import io.opentelemetry.api.trace.Span;
import io.opentelemetry.api.trace.Tracer;
Expand All @@ -42,11 +43,13 @@
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.Timeout;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.jupiter.api.extension.RegisterExtension;
import org.mockito.ArgumentMatchers;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import org.mockito.junit.jupiter.MockitoSettings;
import org.mockito.quality.Strictness;
import org.slf4j.event.Level;

@SuppressWarnings("PreferJavaTimeOverload")
@ExtendWith(MockitoExtension.class)
Expand All @@ -62,9 +65,13 @@ class BatchSpanProcessorTest {
@Mock private Sampler mockSampler;
@Mock private SpanExporter mockSpanExporter;

@RegisterExtension
LogCapturer logs = LogCapturer.create().captureForType(BatchSpanProcessor.class);

@BeforeEach
void setUp() {
when(mockSpanExporter.shutdown()).thenReturn(CompletableResultCode.ofSuccess());
when(mockSpanExporter.export(anyList())).thenReturn(CompletableResultCode.ofSuccess());
}

@AfterEach
Expand Down Expand Up @@ -232,6 +239,32 @@ void exportMoreSpansThanTheBufferSize() {
span6.toSpanData()));
}

@Test
void droppedSpanIsLogged() {
sdkTracerProvider =
SdkTracerProvider.builder()
.addSpanProcessor(
BatchSpanProcessor.builder(mockSpanExporter)
.setMaxQueueSize(1)
.setMaxExportBatchSize(1_000)
.setScheduleDelay(Duration.ofDays(1))
.build())
.build();

// Fill the queue with the first span, then drop 2 more.
createEndedSpan(SPAN_NAME_1);
createEndedSpan(SPAN_NAME_2);
createEndedSpan(SPAN_NAME_2);

// Force export to trigger the drop count log.
sdkTracerProvider.forceFlush().join(10, TimeUnit.SECONDS);

logs.assertContains(
loggingEvent -> loggingEvent.getLevel().equals(Level.WARN),
"BatchSpanProcessor dropped 2 span(s) since the last export"
+ " because the queue is full (maxQueueSize=1)");
}

@Test
void forceExport() {
WaitingSpanExporter waitingSpanExporter =
Expand Down