[Java] Propagate record ID and offset from Windmill context to WindowedValue #37232

Suvrat1629 · 2026-01-06T13:53:02Z

Please add a meaningful description for your change here

Propagate element-level metadata (record ID and offset) from Windmill to WindowedValue in UngroupedWindmillReader
This change extracts the record ID and record offset that are already available in StreamingModeExecutionContext (populated from Windmill messages) and passes them into the created WindowedValue objects.

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gemini-code-assist · 2026-01-06T13:53:19Z

Summary of Changes

Hello @Suvrat1629, 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 addresses issue #37030 by enhancing the Apache Beam Dataflow runner's ability to carry essential element-level metadata. It ensures that the record ID and offset, originating from Windmill messages, are correctly extracted and attached to WindowedValue objects. This fundamental change provides richer context for data elements, which is vital for advanced processing capabilities such as offset-based deduplication in streaming pipelines.

Highlights

Metadata Propagation: This pull request enables the propagation of element-level metadata, specifically record ID and offset, from the Windmill context to WindowedValue objects within the UngroupedWindmillReader.
Contextual Data Extraction: The changes extract the record ID and record offset from the StreamingModeExecutionContext (where they are populated from Windmill messages) and pass them into the WindowedValue objects being created.
Support for Offset-Based Deduplication: The propagated metadata is crucial for supporting features like offset-based deduplication, ensuring that unique data elements can be identified and processed correctly.

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github-actions · 2026-01-06T15:08:23Z

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Suvrat1629 · 2026-01-07T04:10:45Z

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github-actions · 2026-01-07T04:11:50Z

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Suvrat1629 · 2026-01-07T04:16:58Z

/gemini review

gemini-code-assist

Code Review

This pull request propagates the record ID and offset from the Windmill context to WindowedValue objects. The changes in UngroupedWindmillReader correctly extract this information from StreamingModeExecutionContext when offset-based deduplication is supported and pass it to WindowedValues.of(). I've added one comment to prevent a potential RuntimeException if an empty record ID is received from the context.

...va/worker/src/main/java/org/apache/beam/runners/dataflow/worker/UngroupedWindmillReader.java

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Suvrat1629 · 2026-01-07T04:24:43Z

/gemini review

gemini-code-assist

Code Review

This pull request aims to propagate the record ID and offset from the Windmill context to WindowedValue objects in UngroupedWindmillReader. This is a valuable addition for enabling features like exactly-once processing. The implementation correctly passes the extracted record ID and offset to WindowedValues.of(). However, I have a significant concern about the source of this metadata. The current approach of reading from StreamingModeExecutionContext seems likely to assign the same ID and offset to all elements within a WorkItem, which would be incorrect. My review comment details this concern and suggests an alternative.

gemini-code-assist · 2026-01-07T04:27:44Z

...va/worker/src/main/java/org/apache/beam/runners/dataflow/worker/UngroupedWindmillReader.java

+      if (context.offsetBasedDeduplicationSupported()) {
+        byte[] rawId = context.getCurrentRecordId();
+        if (rawId != null && rawId.length > 0) {
+          recordId = new String(rawId, StandardCharsets.UTF_8);
+        }
+        byte[] rawOffset = context.getCurrentRecordOffset();
+        if (rawOffset != null && rawOffset.length == Longs.BYTES) {
+          recordOffset = Longs.fromByteArray(rawOffset);
+        }
+      }


This logic for retrieving record ID and offset from StreamingModeExecutionContext appears to have a potential flaw. The UngroupedWindmillReaderIterator iterates over messages within a WorkItem, but the underlying activeReader in the context (from which getCurrentRecordId and getCurrentRecordOffset get their values) does not appear to be advanced per message. This will likely result in all elements from the same WorkItem receiving the same record ID and offset, which would be incorrect for element-level metadata and could break features like deduplication.

A more robust approach would be to extract the record ID and offset directly from the Windmill.InputMessageBundle for each message, if this information is available there. This would ensure that each element gets its unique metadata.

stankiewicz · 2026-01-08T10:00:12Z

hi Suvrak,

purpose of the issue was to track changes around https://github.com/apache/beam/blob/v2.70.0/runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/UngroupedWindmillReader.java#L135
where we have several context items in ElementMetadata that has to land in WindowedValue.
ElementMetadata is used as transport structure between stages.
offset and record_id id you've added are not part of it, they are not read from windmill so this change is wrong.
In 2.71/master todo was removed from the code (https://github.com/apache/beam/blob/master/runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/UngroupedWindmillReader.java) and you can see drain being propagated from ElementMetadata.
In the future we will be adding new context pieces like tracing context and cdc info.

Suvrat1629 · 2026-01-08T11:56:18Z

@stankiewicz
Thanks for the clarification — I see now that recordId/offset are Dataflow-specific and not in ElementMetadata. Should I close this PR, or is there a separate need for propagating these?

stankiewicz · 2026-01-08T12:41:47Z

I think you can close this PR. Thank you for looking into this!

github-actions bot added runners dataflow labels Jan 6, 2026

Suvrat1629 added 2 commits January 6, 2026 21:09

additional metadata

e9d048f

minor import fix

eba0eac

Suvrat1629 force-pushed the context-switch branch from 3a189b6 to eba0eac Compare January 6, 2026 15:59

Suvrat1629 added 2 commits January 6, 2026 21:32

fix

f718f9c

minor changes

300f50c

github-actions bot added the Next Action: Reviewers label Jan 7, 2026

gemini-code-assist bot reviewed Jan 7, 2026

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...va/worker/src/main/java/org/apache/beam/runners/dataflow/worker/UngroupedWindmillReader.java Outdated Show resolved Hide resolved

addressing gemini comments

3e97f03

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

gemini-code-assist bot reviewed Jan 7, 2026

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Suvrat1629 closed this Jan 8, 2026

[Java] Propagate record ID and offset from Windmill context to WindowedValue #37232

[Java] Propagate record ID and offset from Windmill context to WindowedValue #37232

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Suvrat1629 commented Jan 6, 2026

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