Apache SeaTunnel Monthly Engineering Digest (May 2026): 87 PRs, Stronger Connectors, Smarter Recovery

Hello SeaTunnel community!

The Apache SeaTunnel May 2026 Monthly Report has finally arrived.

According to community statistics, a total of 87 pull requests were merged into the apache/seatunnel repository during May 2026. This month’s primary focus was on continuously improving Connector-V2, closing functional gaps, and making connectors truly production-ready. Significant efforts were also invested in the Zeta Engine, with enhancements across high availability, fault recovery, observability, and testing. At the same time, the community strengthened CI security and regression testing to ensure efficient and reliable development on the main branch.

This report includes:

• A comprehensive review of all merged PRs, covering new features, performance improvements, bug fixes, and architectural enhancements (including the complete PR list).
• In-depth analysis of key technical changes, their implementation details, and impact scope (with patch-level code snippets).
• Reproducible methodologies for performance and stability validation (without fabricated benchmark results).
• Insights into project evolution trends and future technical directions.
• A complete list of all contributors who submitted merged PRs in May 2026, including GitHub usernames, contribution categories, and rankings.

1. Overall Snapshot

1.1 Four-Dimensional Statistics (87 PRs)

The data clearly shows that May was a month focused on making existing capabilities robust and production-ready. A large portion of the merged work addressed real-world operational challenges, including HA, recovery mechanisms, edge cases, resource and memory risks, and observability.

1.2 Module Distribution

• seatunnel-connectors-v2: 32
• seatunnel-engine: 21
• seatunnel-connectors-v2/connector-cdc: 8
• seatunnel-e2e: 6
• docs: 3
• other: 17

2. Feature Enhancements and Engineering Evolution

2.1 Connector-V2: HTTP Source Now Supports Binary Downloads (#10956)

This is one of the most user-visible connector enhancements introduced this month. HTTP Source has evolved from simply fetching JSON and text payloads to supporting full file and binary downloads.

The PR patch summary confirms the scope of the change (15 files changed, +758/-17):

• Added format = "binary"
• Added binary_chunk_size (default: 10 MB) for large-file chunking
• Introduced a fixed output schema: (data: bytes, relativePath: string, partIndex: long)
• Limited to BATCH mode
• Added comprehensive unit tests, E2E tests, and documentation in both Chinese and English

Official example:

env {
  parallelism = 1
  job.mode = "BATCH"
}

source {
  Http {
    url = "http://example.com/files/report.pdf"
    method = "GET"
    format = "binary"
    binary_chunk_size = 10485760
    schema = {
      fields {
        data = bytes
        relativePath = string
        partIndex = long
      }
    }
  }
}

sink {
  LocalFile {
    path = "/tmp/download"
    file_format = "binary"
  }
}

Impact and upgrade recommendations:

• Existing jobs remain unaffected as long as format=text continues to be used.
• After upgrading, users should validate that downstream transforms and sinks properly handle bytes fields.
• For large files, binary_chunk_size reduces peak memory usage from file-size scale to chunk-size scale, significantly lowering OOM risk. This can be validated through RSS and GC metrics.

2.2 Engine/Zeta: Progressive Validation for Dry-Run Mode (#10763)

[Feature][Zeta] Implement proper dry-run mode with progressive validation layer0

Engineering value:

• Configuration errors are detected before job submission or startup rather than during runtime.
• Provides a foundation for future progressive validation layers, including connector parameter validation, schema constraint verification, and permission/resource prechecks.

2.3 Ecosystem Expansion and Tooling Improvements

This month also saw progress in control-plane capabilities, observability, edge collection, and developer tooling:

• #10878: STIP-24 Phase 1 EdgeSocket ingress (Edge Collection MVP)
• #10491: Data lineage and performance tracing
• #10184: Python SDK Client for SeaTunnel REST API
• Multi-table and schema evolution support for RabbitMQ, Cassandra, SQL Server CDC, Postgres CDC, and more

3. Performance Optimization and Resource Risk Mitigation

3.1 Kudu: Dependency Upgrade Resolves Flink 1.15+ Compatibility Risks (#10974)

This PR primarily improves compatibility and runtime reliability, although it was categorized as a performance improvement.

Implementation details:

• Upgraded kudu-client to reduce classpath conflicts with Flink 1.15+.
• Removed explicit dependencies on Kudu’s shaded Guava libraries to avoid runtime issues caused by internal shaded API changes.

Suggested reproducible validation:

Run identical Kudu jobs on Flink 1.15+ and compare:

• Job startup success rate
• Startup latency percentiles (P50/P95)
• Stability during 30-minute execution windows
• Presence of slot allocation or release loops

3.2 Kafka: Reduce Default Cache Queue Size from 1024 to 2 to Prevent OOM (#10954)

The PR title explicitly states:

Reduce default reader_cache_queue_size from 1024 to 2 to prevent OOM

Quantitative interpretation:

• Queue depth reduced by 512x (1024 → 2).
• For workloads with large cached records (such as deserialized rows), this significantly reduces peak memory usage and GC pressure.

Recommended metrics:

• Peak RSS memory
• GC frequency
• Young/Old GC duration
• OOM occurrence rate
• Throughput (rows/sec)

4. Bug Fixes and Architectural Improvements Defined May

4.1 Zeta: Master Failover Could Permanently Stall Jobs (#10836)

The PR title already highlights the affected scenarios:

affects BATCH / bounded source / job shutdown phase

Potential production impact:

• Jobs that should terminate may remain indefinitely stuck.
• Increased risk of resource leakage.
• Potential duplicate scheduling.
• Higher risk of inconsistent downstream results.

Recommended validation:

After simulating master failover or node failure, verify:

• Jobs complete the shutdown phase correctly.
• Final job states remain consistent.
• State cleanup does not suffer from race conditions.

4.2 Security Fix: Path Traversal Vulnerability in Log REST API (#10628)

[Fix][Zeta] Fix path traversal vulnerability in log file REST API endpoints

Operational recommendations:

• Apply access controls at gateway or ingress layers.
• Restrict log API access to authorized users only.
• Validate the fix using security scans and path traversal attempts such as ../.

4.3 Recovery and Race Condition Improvements (#10687 / #10842 / #10877)

Collectively, these fixes significantly strengthened Zeta’s recovery workflows, particularly around:

• State cleanup after node failures
• Restore process consistency
• Reuse of recovery metadata
• Elimination of race conditions

5. Deep Dive into Key Technical Changes

5.1 HTTP Binary Download Support (#10956): Design, Semantics, and Impact

Key characteristics:

• format=binary treats the HTTP response body as raw bytes.
• binary_chunk_size controls chunking for large files.
• Fixed output schemas simplify downstream sink implementations.
• Batch-only mode avoids ambiguity with streaming download semantics.

User value:

HTTP Source can now fetch both API data and files, reducing pipeline complexity.

Risks and recommendations:

After chunking, downstream sinks must correctly reconstruct files using the combination of relativePath and partIndex. The official binary file sink or sinks supporting byte-stream writes are strongly recommended.

5.2 SQLite Upsert Syntax Fix (#10880): Why EXCLUDED Matters

SQLite's UPSERT syntax requires conflicting updates to reference EXCLUDED.<column> rather than VALUES(<column>).

The PR updates the generated SQL as follows:

- `col`=VALUES(`col`)
+ `col`=EXCLUDED.`col`

Unit tests were added to ensure correctness and prevent regressions.

5.3 Milvus Exception Reference Fix (#10975): A Small Change with Large Operational Value

A single-line change delivers a significant troubleshooting improvement:

- loadStateResponse.getException()
+ queryResultsR.getException()

After the fix, error messages accurately reflect the actual failure source, reducing debugging effort and avoiding misleading diagnostics.

5.4 Zeta Flaky Test Fix (#10891): Eliminating Timing Dependencies

The patch replaces real job submissions and asynchronous waiting with:

• Mock servers
• Mock JobHistoryService
• Constructed pendingJobDAGInfo objects

This removes non-deterministic timing dependencies and significantly improves CI stability.

6. Reproducible Framework for Performance and Stability Validation

Many of May’s PRs focused on compatibility improvements, stability enhancements, and safer default configurations rather than benchmark-oriented optimizations.

To ensure objective validation:

• Default parameter changes: measure RSS, GC, OOM rate, and throughput.
• Chunking strategies: measure peak memory, end-to-end latency, and output consistency.
• Dependency upgrades: measure startup success rate, startup latency percentiles, and long-term stability.

Recommended validation workflow:

1. Fix dataset size and parallelism.
2. Fix hardware and network environments.
3. Define consistent metrics.
4. Compare only pre-change and post-change versions.
5. Preserve all logs and metric outputs.

Thanks to All Contributors

Apache SeaTunnel’s continuous growth and evolution would not be possible without every community member who contributes code, reviews, documentation, and ideas.

Thank you all for your dedication and generosity. Every line of code helps move the project forward and strengthens the ecosystem.

The following contributors made merged contributions during May 2026:

(The ranking is based on the number of merged PRs during May. Contribution categories are aggregated using the four-quadrant classification adopted in this report.)