jtuglu-netflix commented on code in PR #17847:
URL: https://github.com/apache/druid/pull/17847#discussion_r2066822234
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server/src/main/java/org/apache/druid/segment/realtime/SegmentGenerationMetrics.java:
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@@ -55,6 +56,23 @@ public class SegmentGenerationMetrics
private final AtomicLong maxSegmentHandoffTime = new
AtomicLong(NO_EMIT_SEGMENT_HANDOFF_TIME);
+ // Message gap accounting
+ private final AtomicLong minMessageGap = new AtomicLong(Long.MAX_VALUE);
+ private final AtomicLong maxMessageGap = new AtomicLong(Long.MIN_VALUE);
+ private final AtomicLong numMessageGap = new AtomicLong(0);
+ private final AtomicDouble avgMessageGap = new AtomicDouble(0);
Review Comment:
> If we keep two separate atomic fields, the snapshotting can potentially be
inconsistent due to race conditions.
Actually, from my understanding, this should never happen. There is a single
writer to these fields(a task is single threaded, and has 1 row appenderator),
and potentially multiple readers (at the moment it's a single reader). The
reader threads simply look at the latter of these atomic fields. The "worst"
case is the avg computation will be 1 row behind.
That being said, I did try your suggestion before and it was a bit slower,
so I opted for this approach:
pair:
```
Benchmark
(enableMessageGapMetrics) Mode Cnt Score Error Units
SegmentGenerationMetricsBenchmark.benchmarkMultipleReportMaxSegmentHandoffTime
true avgt 2 1.688 ns/op
SegmentGenerationMetricsBenchmark.benchmarkMultipleReportMaxSegmentHandoffTime
false avgt 2 1.701 ns/op
SegmentGenerationMetricsBenchmark.benchmarkMultipleReportMessageGap
true avgt 2 11.681 ns/op
SegmentGenerationMetricsBenchmark.benchmarkMultipleReportMessageGap
false avgt 2 11.836 ns/op
```
two atomics:
```
Benchmark
(enableMessageGapMetrics) Mode Cnt Score Error Units
SegmentGenerationMetricsBenchmark.benchmarkMultipleReportMaxSegmentHandoffTime
true avgt 2 1.690 ns/op
SegmentGenerationMetricsBenchmark.benchmarkMultipleReportMaxSegmentHandoffTime
false avgt 2 1.687 ns/op
SegmentGenerationMetricsBenchmark.benchmarkMultipleReportMessageGap
true avgt 2 8.816 ns/op
SegmentGenerationMetricsBenchmark.benchmarkMultipleReportMessageGap
false avgt 2 8.824 ns/op
```
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