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Do not emit negative lag because of stale offsets #14292

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merged 8 commits into from
Jul 5, 2023
Merged

Do not emit negative lag because of stale offsets #14292

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13df220
Do not emit negative lag because of stale offsets
AmatyaAvadhanula May 16, 2023
2ef4257
Revert accidental deletion
AmatyaAvadhanula May 16, 2023
45d86b1
Fix forbidden API and log message
AmatyaAvadhanula May 17, 2023
4b2dab6
Remove previous log message
AmatyaAvadhanula May 17, 2023
e98101c
Fix forbidden api in test
AmatyaAvadhanula May 17, 2023
1f7512e
Merge remote-tracking branch 'upstream/master' into fixNegativeLag
AmatyaAvadhanula May 29, 2023
d2688ef
Merge remote-tracking branch 'upstream/master' into fixNegativeLag
AmatyaAvadhanula Jun 27, 2023
bd8aaa1
Less noisy logs and use UTC times in tests
AmatyaAvadhanula Jun 27, 2023
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15 changes: 15 additions & 0 deletions ...in/java/org/apache/druid/indexing/seekablestream/supervisor/SeekableStreamSupervisor.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4220,6 +4220,21 @@ protected void emitLag()
return;
}

// Try emitting lag even with stale metrics provided that none of the partitions has negative lag
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Suggested change
// Try emitting lag even with stale metrics provided that none of the partitions has negative lag
// Try emitting lag even with stale metrics provided that none of the partitions have negative lag

final long staleMillis = sequenceLastUpdated == null
? 0
: DateTimes.nowUtc().getMillis()
- (tuningConfig.getOffsetFetchPeriod().getMillis() + sequenceLastUpdated.getMillis());
if (staleMillis > 0 && partitionLags.values().stream().anyMatch(x -> x < 0)) {
// Log at most once every twenty supervisor runs to reduce noise in the logs
if ((staleMillis / getIoConfig().getPeriod().getMillis()) % 20 == 0) {
log.warn("Lag is negative and will not be emitted because topic offsets have become stale. "
+ "This will not impact data processing. "
+ "Offsets may become stale because of connectivity issues.");
}
return;
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@abhishekrb19 abhishekrb19 May 19, 2023 •
edited
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Should we skip emitting lag metrics only for the stale partitions? I think in general, it'll be helpful to emit metrics for partitions that have non-negative lag. For example, if a topic's partitions are spread across multiple brokers and only some have connectivity issues. Or for a topic where some partitions receive little to no data, those may selectively be considered "stale".

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If we do that, it will be very easy to get into a wrong debugging trail where the overall lag might appear lower than it actually is. I am in favor of not emitting lag for any partition at all. The partition level lag would still be available in the task reports.

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I think there is a separate metric which we can emit for partition-level lag, without actually reporting/affecting the overall lag at all. But I guess having them in the report should be enough too.

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@abhishekrb19 abhishekrb19 May 22, 2023 •
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Yeah, a per-partition lag metric would complement the existing metrics. My main concern with not reporting any lag for a topic in this scenario is we'd have periods of missing lag data for as long as there's at least one stale partition in a topic. The missing metrics data can hide problems silently and affect existing downstream consumers of the data on how they alert, present metrics for visualization, etc. What do you think?

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a missing metric data for a topic is easier to detect and be notified about than metric data missing some partitions. @AmatyaAvadhanula - do we already emit a lag metric for each partition in the topic?

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Yes, we do emit metrics for every partition

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These partitions usually go stale because supervisor can't connect to Kafka. We can revisit later if not having any metric becomes a pain point. ideally, users should also be alerting on missing metric.

}

LagStats lagStats = computeLags(partitionLags);
Map<String, Object> metricTags = spec.getContextValue(DruidMetrics.TAGS);
for (Map.Entry<PartitionIdType, Long> entry : partitionLags.entrySet()) {
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25 changes: 25 additions & 0 deletions ...rg/apache/druid/indexing/seekablestream/supervisor/SeekableStreamSupervisorStateTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,7 @@
import org.apache.druid.indexing.seekablestream.supervisor.SeekableStreamSupervisorStateManager.SeekableStreamExceptionEvent;
import org.apache.druid.indexing.seekablestream.supervisor.SeekableStreamSupervisorStateManager.SeekableStreamState;
import org.apache.druid.indexing.seekablestream.supervisor.autoscaler.AutoScalerConfig;
import org.apache.druid.java.util.common.DateTimes;
import org.apache.druid.java.util.common.ISE;
import org.apache.druid.java.util.common.StringUtils;
import org.apache.druid.java.util.common.granularity.Granularities;
Expand Down Expand Up @@ -1035,6 +1036,30 @@ public void testGetStats()
);
}

@Test
public void testStaleOffsetsNegativeLagNotEmitted() throws Exception
{
expectEmitterSupervisor(false);

CountDownLatch latch = new CountDownLatch(1);

final TestEmittingTestSeekableStreamSupervisor supervisor = new TestEmittingTestSeekableStreamSupervisor(
latch,
TestEmittingTestSeekableStreamSupervisor.LAG,
// Record lag must not be emitted
ImmutableMap.of("0", 10L, "1", -100L),
null
);
supervisor.start();
// Forcibly set the offsets to be stale
supervisor.sequenceLastUpdated = DateTimes.nowUtc().minus(Integer.MAX_VALUE);

latch.await();

supervisor.emitLag();
Assert.assertEquals(0, emitter.getEvents().size());
}

private List<Event> filterMetrics(List<Event> events, List<String> whitelist)
{
List<Event> result = events.stream()
Expand Down