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[KafkaIO] Only update size metrics once per batch#36077

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kennknowles merged 1 commit intoapache:masterfrom
sjvanrossum:kafkaio-batched-metric-updates
Sep 9, 2025
Merged

[KafkaIO] Only update size metrics once per batch#36077
kennknowles merged 1 commit intoapache:masterfrom
sjvanrossum:kafkaio-batched-metric-updates

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@sjvanrossum
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Unbatched updates for distribution of record sizes take up a surprising amount of CPU time, >3% CPU time at 50th percentile.
Unbatched updates for average record size takes up >0.3% CPU time at 50th percentile, which isn't huge but still worth fixing while we're at it.

Performing these updates once per batch reduces CPU time at 50th percentile to 0.2% for the distribution and 0.02% for the average.


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Summary of Changes

Hello @sjvanrossum, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant performance improvement for KafkaIO by optimizing how record size metrics are updated. Instead of updating these metrics for each individual record, the system now aggregates the necessary data within a batch and performs a single, consolidated update. This change aims to reduce CPU overhead and enhance the overall efficiency of Kafka data processing within Apache Beam.

Highlights

  • Performance Optimization: Updates to record size metrics (distribution and average) are now batched, significantly reducing CPU time previously spent on unbatched updates. This change improves efficiency by updating metrics once per batch rather than per individual record.
  • KafkaIOUtils Refactoring: The MovingAverage utility class in KafkaIOUtils.java has been enhanced with a new update method that accepts a sum and count, enabling batch updates. The existing single-quantity update method was also refined.
  • ReadFromKafkaDoFn Metric Collection: The ReadFromKafkaDoFn now accumulates record size metrics (sum, count, min, max) for an entire batch of Kafka records before performing a single update to the avgRecordSize and rawSizes metrics. This replaces the previous per-record update approach.
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github-actions bot commented Sep 6, 2025

Assigning reviewers:

R: @kennknowles for label java.
R: @johnjcasey for label kafka.

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@sjvanrossum
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Sampled on a pipeline with 4 initial machines (AMD Milan/Rome, 4 vCPUs per machine) processing a topic receiving 1GiB/s across 500 partitions (1KiB record size) starting with 2TiB backlog plumbed straight to /dev/null. I think it's worth revisiting the metrics implementation, fetching the delegate metric for every update is an unnecessary waste. For this stress test I observed a 25% throughput improvement in ReadFromKafkaDoFn after these changes were applied.

Profiler data for distribution of record sizes before:
image
And after:
image

Profiler data for average record size before:
image
And after:
image

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Those are some surprising numbers. Are there integration tests we can run? (by touching files in .github/trigger_files corresponding to workflows to run)

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I see we have a dedicated precommit. I am happy to merge and we can watch for any integration test failures.

@kennknowles kennknowles merged commit 60630af into apache:master Sep 9, 2025
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@sjvanrossum sjvanrossum deleted the kafkaio-batched-metric-updates branch September 10, 2025 10:28
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