Iceberg CDC streaming source #37191

ahmedabu98 · 2025-12-26T17:51:57Z

No description provided.

gemini-code-assist · 2025-12-26T17:52:26Z

Summary of Changes

Hello @ahmedabu98, 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 delivers a robust Iceberg Change Data Capture (CDC) streaming source for Apache Beam. It allows Beam pipelines to consume a continuous stream of changes from an Iceberg table, including inserts, deletes, and updates. The implementation intelligently handles different types of change events, processing straightforward additions or removals directly, while employing a sophisticated reconciliation step for complex update scenarios. This significantly expands Beam's capabilities for real-time data integration with Iceberg.

Highlights

New CDC Streaming Source: Introduced a comprehensive Change Data Capture (CDC) streaming source for Iceberg tables, enabling continuous processing of data modifications (inserts, deletes, updates) within Apache Beam pipelines.
Changelog Task Processing: Implemented a mechanism to scan incremental Iceberg snapshots and categorize changelog tasks into 'uniform' (all inserts or all deletes) and 'mixed' (both inserts and deletes for the same record) for optimized processing.
Data Reconciliation for Updates: Developed a reconciliation process for 'mixed' changelog tasks, using co-grouping by record ID to accurately identify and emit 'UPDATE_BEFORE' and 'UPDATE_AFTER' records, alongside pure inserts and deletes.
Enhanced Read Utilities: Extended ReadUtils with new methods and classes (DeleteReader, BeamDeleteFilter, BeamDeleteReader) to support reading and filtering based on Iceberg delete files, crucial for CDC functionality.
Serialization of Iceberg Metadata: Added new serializable classes (SerializableDeleteFile, SerializableChangelogTask, ChangelogDescriptor) to efficiently transfer Iceberg metadata and task information across Beam workers.
Increased Component Visibility: Adjusted the visibility of key classes and methods in IncrementalScanSource and SerializableDataFile to public or protected, facilitating their reuse and extension within the new CDC framework.

🧠 New Feature in Public Preview: You can now enable Memory to help Gemini Code Assist learn from your team's feedback. This makes future code reviews more consistent and personalized to your project's style. Click here to enable Memory in your admin console.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	`/gemini review`	Performs a code review for the current pull request in its current state.
Pull Request Summary	`/gemini summary`	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	`/gemini help`	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

ahmedabu98 · 2025-12-26T18:07:15Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a significant new feature: an Iceberg CDC (Change Data Capture) streaming source. The overall design is solid, leveraging Beam's splittable DoFns and CoGroupByKey for reconciling changes. The code is well-structured into different components for scanning, reading, and reconciling changelogs.

I've identified a few areas for improvement, mainly around cleaning up TODO comments and debugging statements. My specific comments are below.

There is one critical issue I couldn't comment on directly due to tooling limitations: in SerializableDataFile.java, the equals and hashCode methods have not been updated to include the newly added fields (dataSequenceNumber, fileSequenceNumber, firstRowId). This violates the Object contract and can lead to subtle bugs. Please ensure this is fixed.

gemini-code-assist · 2025-12-26T18:09:47Z

sdks/java/io/iceberg/src/main/java/org/apache/beam/sdk/io/iceberg/ReadUtils.java

+    // TODO: remove this (unused)
+    @SuppressWarnings("method.invocation")
+    public BeamDeleteFilter(
+        FileIO io,
+        SerializableChangelogTask scanTask,
+        Schema tableSchema,
+        Schema projectedSchema,
+        List<DeleteFile> deleteFiles) {
+      super(scanTask.getDataFile().getPath(), deleteFiles, tableSchema, projectedSchema);
+      this.io = io;
+      this.asStructLike = new InternalRecordWrapper(requiredSchema().asStruct());
+    }
+
+    // TODO: remove this (unused)
+    @SuppressWarnings("method.invocation")
+    public BeamDeleteFilter(FileIO io, ContentScanTask<?> scanTask, List<DeleteFile> deleteFiles) {
+      super(
+          scanTask.file().location(),
+          deleteFiles,
+          scanTask.spec().schema(),
+          scanTask.spec().schema());
+      this.io = io;
+      this.asStructLike = new InternalRecordWrapper(requiredSchema().asStruct());
+    }


These constructors are marked as unused with a TODO to remove them. To improve code clarity and maintainability, they should be removed.

gemini-code-assist · 2025-12-26T18:09:47Z

sdks/java/io/iceberg/src/main/java/org/apache/beam/sdk/io/iceberg/ReadUtils.java

+    // TODO: remove this (unused)
+    @SuppressWarnings("method.invocation")
+    public BeamDeleteReader(
+        FileIO io,
+        SerializableChangelogTask scanTask,
+        Schema tableSchema,
+        Schema projectedSchema,
+        List<DeleteFile> deleteFiles) {
+      super(scanTask.getDataFile().getPath(), deleteFiles, tableSchema, projectedSchema);
+      this.io = io;
+      this.asStructLike = new InternalRecordWrapper(requiredSchema().asStruct());
+    }
+
+    // TODO: remove this (unused)
+    @SuppressWarnings("method.invocation")
+    public BeamDeleteReader(FileIO io, ContentScanTask<?> scanTask, List<DeleteFile> deleteFiles) {
+      super(
+          scanTask.file().location(),
+          deleteFiles,
+          scanTask.spec().schema(),
+          scanTask.spec().schema());
+      this.io = io;
+      this.asStructLike = new InternalRecordWrapper(requiredSchema().asStruct());
+    }


These constructors are marked as unused with a TODO to remove them. To improve code clarity and maintainability, they should be removed.

gemini-code-assist · 2025-12-26T18:09:47Z

sdks/java/io/iceberg/src/main/java/org/apache/beam/sdk/io/iceberg/cdc/ChangelogScanner.java

+    // TODO: use TableCache here
+    Table table = scanConfig.getTable();


The TODO comment suggests using TableCache. This is a good practice to avoid repeatedly loading table metadata, which can be expensive. Please use TableCache.get(element.getKey()) here. You will also need to add a @Setup method to initialize the TableCache with TableCache.setup(scanConfig);.

Suggested change

// TODO: use TableCache here

Table table = scanConfig.getTable();

Table table = TableCache.get(element.getKey());

gemini-code-assist · 2025-12-26T18:09:47Z

sdks/java/io/iceberg/src/main/java/org/apache/beam/sdk/io/iceberg/cdc/ReadFromChangelogs.java

+    // TODO: use TableCache
+    Table table = scanConfig.getTable();


The TODO comment suggests using TableCache. This is a good practice to avoid repeatedly loading table metadata. Please use TableCache.get(element.getKey().getTableIdentifierString()) here. You will also need to add TableCache.setup(scanConfig); to the @Setup method.

Suggested change

// TODO: use TableCache

Table table = scanConfig.getTable();

Table table = TableCache.get(element.getKey().getTableIdentifierString());

gemini-code-assist · 2025-12-26T18:09:47Z

sdks/java/io/iceberg/src/main/java/org/apache/beam/sdk/io/iceberg/cdc/ReadFromChangelogs.java

+      Row id = structToBeamRow(ordinal, recId, recordIdSchema, rowIdWithOrdinalBeamSchema);
+      outputReceiver.get(keyedTag).outputWithTimestamp(KV.of(id, row), timestamp);
+    } else { // fast path
+      System.out.printf("[UNIFORM] -- Output(%s, %s)\n%s%n", ordinal, timestamp, row);


This System.out.printf seems to be for debugging and should be removed before merging.

gemini-code-assist · 2025-12-26T18:09:47Z

sdks/java/io/iceberg/src/main/java/org/apache/beam/sdk/io/iceberg/cdc/ReconcileChanges.java

+    if (hasInserts && hasDeletes) {
+      // UPDATE: row ID exists in both streams
+      // - emit all deletes as 'UPDATE_BEFORE', and all inserts as 'UPDATE_AFTER'
+      // - emit extra inserts as 'UPDATE_AFTER'
+      // - ignore extra deletes (TODO: double check if this is a good decision)
+      Iterator<TimestampedValue<Row>> deletesIterator = deletes.iterator();
+      Iterator<TimestampedValue<Row>> insertsIterator = inserts.iterator();
+      while (deletesIterator.hasNext() && insertsIterator.hasNext()) {
+        // TODO: output as UPDATE_BEFORE kind
+        TimestampedValue<Row> updateBefore = deletesIterator.next();
+        out.outputWithTimestamp(updateBefore.getValue(), updateBefore.getTimestamp());
+        System.out.printf("[MIXED] -- UpdateBefore\n%s\n", updateBefore);
+
+        // TODO: output as UPDATE_AFTER kind
+        TimestampedValue<Row> updateAfter = insertsIterator.next();
+        out.outputWithTimestamp(updateAfter.getValue(), updateAfter.getTimestamp());
+        System.out.printf("[MIXED] -- UpdateAfter\n%s\n", updateAfter);
+      }
+      while (insertsIterator.hasNext()) {
+        // TODO: output as UPDATE_AFTER kind
+        TimestampedValue<Row> insert = insertsIterator.next();
+        out.outputWithTimestamp(insert.getValue(), insert.getTimestamp());
+        System.out.printf("[MIXED] -- Added(extra)\n%s\n", insert);
+      }
+    } else if (hasInserts) {
+      // INSERT only
+      for (TimestampedValue<Row> rec : inserts) {
+        System.out.printf("[MIXED] -- Added\n%s\n", rec);
+        out.outputWithTimestamp(rec.getValue(), rec.getTimestamp());
+      }
+    } else if (hasDeletes) {
+      // DELETE only
+      for (TimestampedValue<Row> rec : deletes) {
+        // TODO: output as DELETE kind
+        System.out.printf("[MIXED] -- Deleted\n%s\n", rec);
+        out.outputWithTimestamp(rec.getValue(), rec.getTimestamp());
+      }
+    }


This method contains several System.out.printf statements that appear to be for debugging. They should be removed before merging.

init

86d8f36

github-actions bot added java io labels Dec 26, 2025

comments

eb23828

gemini-code-assist bot reviewed Dec 26, 2025

View reviewed changes

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Iceberg CDC streaming source #37191

Iceberg CDC streaming source #37191

Uh oh!

ahmedabu98 commented Dec 26, 2025

Uh oh!

gemini-code-assist bot commented Dec 26, 2025

Uh oh!

ahmedabu98 commented Dec 26, 2025

Uh oh!

gemini-code-assist bot left a comment

Uh oh!

gemini-code-assist bot Dec 26, 2025

Uh oh!

gemini-code-assist bot Dec 26, 2025

Uh oh!

gemini-code-assist bot Dec 26, 2025

Uh oh!

gemini-code-assist bot Dec 26, 2025

Uh oh!

gemini-code-assist bot Dec 26, 2025

Uh oh!

gemini-code-assist bot Dec 26, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

		// TODO: use TableCache here
		Table table = scanConfig.getTable();

	// TODO: use TableCache here
	Table table = scanConfig.getTable();
	Table table = TableCache.get(element.getKey());

	// TODO: use TableCache
	Table table = scanConfig.getTable();
	Table table = TableCache.get(element.getKey().getTableIdentifierString());

Iceberg CDC streaming source #37191

Are you sure you want to change the base?

Iceberg CDC streaming source #37191

Uh oh!

Conversation

ahmedabu98 commented Dec 26, 2025

Uh oh!

gemini-code-assist bot commented Dec 26, 2025

Summary of Changes

Highlights

Footnotes

Uh oh!

ahmedabu98 commented Dec 26, 2025

Uh oh!

gemini-code-assist bot left a comment

Choose a reason for hiding this comment

Code Review

Uh oh!

gemini-code-assist bot Dec 26, 2025

Choose a reason for hiding this comment

Uh oh!

gemini-code-assist bot Dec 26, 2025

Choose a reason for hiding this comment

Uh oh!

gemini-code-assist bot Dec 26, 2025

Choose a reason for hiding this comment

Uh oh!

gemini-code-assist bot Dec 26, 2025

Choose a reason for hiding this comment

Uh oh!

gemini-code-assist bot Dec 26, 2025

Choose a reason for hiding this comment

Uh oh!

gemini-code-assist bot Dec 26, 2025

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant