[darshan-sj]

Summary & Motivation

In the Cloud_Spanner_to_GCS_Avro (ExportPipeline) template, ExportTransform writes exported Spanner rows to GCS using AvroIO.writeCustomTypeToGenericRecords() with dynamic table destinations (SchemaBasedDynamicDestinations) and runner-determined sharding.

By default, WriteFiles caps the number of concurrently open writers per bundle at 20 (DEFAULT_MAX_NUM_WRITERS_PER_BUNDLE). When exporting Spanner databases with a large number of tables, a bundle can encounter more than 20 distinct table destinations, causing more frequent writer evictions (or shuffle spilling) and resulting in smaller, more fragmented output Avro files.

This PR configures .withMaxNumWritersPerBundle(50) on the AvroIO write transform in ExportTransform to allow up to 50 concurrent open writers per bundle, reducing writer turnover and producing fewer, larger Avro files while keeping worker memory bounded.

Changes Made

• ExportTransform.java:
  • Added .withMaxNumWritersPerBundle(50).

---

Testing

• Unit Tests:
  • Verified ExportTransformTest (11 tests) and VerifyDataBoostParallelismTest (9 tests) pass.
• End-to-End Template Execution:
  • Staged Cloud_Spanner_to_GCS_Avro and ran a batch Dataflow export job against Cloud Spanner database, verifying all Avro files (~1.81 GiB) were exported to GCS without errors.

[gemini-code-assist]

Summary of Changes

Hello, 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 improves the efficiency of the Cloud Spanner to Avro export pipeline by adjusting the writer concurrency settings. By allowing more concurrent writers, the pipeline can better handle databases with a high number of tables, resulting in fewer and larger output files while maintaining memory stability. The change also includes a necessary update to the underlying Apache Beam SDK version.

Highlights

• Performance Optimization: Increased the maximum number of concurrent writers per bundle to 50 to reduce writer turnover and file fragmentation during large Spanner exports.
• Dependency Update: Updated the Apache Beam SDK core dependency to version 2.78.0-SNAPSHOT in the project configuration.

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[gemini-code-assist]

Code Review

This pull request updates the v1/pom.xml to specify a SNAPSHOT version for beam-sdks-java-core and modifies ExportTransform.java to configure the Avro write transform with withMaxNumWritersPerBundle(50) and withEvictWritersWhenFull(). I have no feedback to provide on these changes.