Migrate gRPC transport executor to ForkJoinPool

[jungeunyooon]

Description

This PR migrates the gRPC transport executor from FixedExecutorBuilder to ForkJoinPoolExecutorBuilder to improve performance through work-stealing and better load balancing.

• Updated GrpcPlugin.java to use ForkJoinPoolExecutorBuilder instead of FixedExecutorBuilder
• Updated test files to reflect the executor change

Related Issues

Resolves #19370

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for cb0269f: FAILURE

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❌ Gradle check result for 32618f4: FAILURE

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[karenyrx]

Thanks for taking this on!

[github-actions]

❌ Gradle check result for 6fafca3: FAILURE

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[jungeunyooon]

@karenyrx I’ve updated the PR based on your feedback.
I’d appreciate it if you could review it again.

[karenyrx]

Overall LGTM, would be great to see an OSB run with/without this change to see if/how much performance improves

[coderabbitai]

📝 Walkthrough

Walkthrough

This change migrates the gRPC transport executor implementation from FixedExecutorBuilder to ForkJoinPoolExecutorBuilder to leverage improved performance benefits such as work-stealing and better load balancing. The migration updates the main plugin code, test files, and changelog documentation.

Changes

Cohort / File(s)	Summary
Main Implementation modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/GrpcPlugin.java	Replaced FixedExecutorBuilder with ForkJoinPoolExecutorBuilder; renamed executorCount variable to parallelism; updated import statement and added Javadoc note about ForkJoinPool approach.
Test Files modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/Netty4GrpcServerTransportTests.java, modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java	Replaced executor builder instantiation from FixedExecutorBuilder(settings, "grpc", 4, 1000, "thread_pool.grpc") to ForkJoinPoolExecutorBuilder("grpc", 4, "thread_pool.grpc"); updated imports accordingly.
Documentation CHANGELOG.md	Added changelog entry documenting the migration to ForkJoinPoolExecutorBuilder for improved gRPC transport performance.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 11.11% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Migrate gRPC transport executor to ForkJoinPool' clearly and concisely summarizes the main objective of the changeset.
Description check	✅ Passed	The PR description provides a clear summary of changes, specifies the related issue (#19370), and completes the required checklist items.
Linked Issues check	✅ Passed	The PR successfully implements the requirements from issue #19370 by migrating from FixedExecutorBuilder to ForkJoinPoolExecutorBuilder across all relevant files.
Out of Scope Changes check	✅ Passed	All changes are directly related to the executor migration objective; the CHANGELOG entry addition is an appropriate administrative change for documenting this migration.

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✨ Finishing touches

• 📝 Generate docstrings

---

📜 Recent review details

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 68c2d14 and a81020d.

📒 Files selected for processing (4)

• CHANGELOG.md
• modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/GrpcPlugin.java
• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/Netty4GrpcServerTransportTests.java
• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java

🧰 Additional context used

🧠 Learnings (7)

📚 Learning: 2025-12-12T18:40:08.452Z

Learnt from: reta
Repo: opensearch-project/OpenSearch PR: 20017
File: plugins/transport-reactor-netty4/src/test/java/org/opensearch/http/reactor/netty4/ssl/SecureReactorNetty4HttpServerTransportTests.java:256-256
Timestamp: 2025-12-12T18:40:08.452Z
Learning: In the OpenSearch ReactorNetty4 secure HTTP transport tests (plugins/transport-reactor-netty4/src/test/java/org/opensearch/http/reactor/netty4/ssl/SecureReactorNetty4HttpServerTransportTests.java), URI limit validation has been moved from the protocol layer to the transport layer, making it protocol-agnostic. The random protocol selection in ReactorHttpClient.https(settings) is intentional to ensure all tests validate correct behavior across HTTP/1.1, HTTP/2, and HTTP/3.

Applied to files:

• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java
• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/Netty4GrpcServerTransportTests.java

📚 Learning: 2025-12-19T21:26:37.090Z

Learnt from: reta
Repo: opensearch-project/OpenSearch PR: 20017
File: modules/transport-netty4/src/main/java/org/opensearch/http/netty4/Netty4QuicServerTransport.java:0-0
Timestamp: 2025-12-19T21:26:37.090Z
Learning: In Netty4QuicServerTransport (modules/transport-netty4/src/main/java/org/opensearch/http/netty4/Netty4QuicServerTransport.java), the secureHttpTransportSettingsProvider parameter is guaranteed to be non-null because the plugin verifies its presence during instantiation, so no explicit null-check is needed in the constructor.

Applied to files:

• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java
• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/Netty4GrpcServerTransportTests.java

📚 Learning: 2025-12-12T13:31:51.234Z

Learnt from: andriyredko
Repo: opensearch-project/OpenSearch PR: 20017
File: plugins/transport-reactor-netty4/src/test/java/org/opensearch/http/reactor/netty4/ssl/SecureReactorNetty4HttpServerTransportTests.java:642-646
Timestamp: 2025-12-12T13:31:51.234Z
Learning: In the OpenSearch ReactorNetty4 secure HTTP transport tests (plugins/transport-reactor-netty4/src/test/java/org/opensearch/http/reactor/netty4/ssl/SecureReactorNetty4HttpServerTransportTests.java), the createBuilderWithPort() helper intentionally uses randomBoolean() for the HTTP/3 enabled setting to ensure all tests validate correct behavior with both HTTP/3 enabled and disabled configurations.

Applied to files:

• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java
• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/Netty4GrpcServerTransportTests.java

📚 Learning: 2025-12-13T20:16:15.318Z

Learnt from: reta
Repo: opensearch-project/OpenSearch PR: 20017
File: modules/transport-netty4/src/main/java/org/opensearch/http/netty4/Netty4Http3ServerTransport.java:101-123
Timestamp: 2025-12-13T20:16:15.318Z
Learning: In OpenSearch, only one HTTP transport implementation can be active and loaded at a time, so duplicate setting definitions (such as h3.max_stream_local_length, h3.max_stream_remote_length, and h3.max_streams) across different transport implementations like Netty4Http3ServerTransport and ReactorNetty4HttpServerTransport will not cause setting registration conflicts.

Applied to files:

• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java
• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/Netty4GrpcServerTransportTests.java

📚 Learning: 2026-01-02T19:23:16.689Z

Learnt from: karenyrx
Repo: opensearch-project/OpenSearch PR: 20335
File: modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/proto/request/search/SearchSourceBuilderProtoUtils.java:155-172
Timestamp: 2026-01-02T19:23:16.689Z
Learning: In OpenSearch's gRPC transport module, treat removals of previously-unsupported fields (those throwing UnsupportedOperationException) from experimental proto schemas as non-breaking changes. When reviewing changes to proto-related Java code in this module, document that such removals do not count as breaking API changes, and ensure tests reflect compatibility expectations accordingly.

Applied to files:

• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java
• modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/GrpcPlugin.java
• modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/Netty4GrpcServerTransportTests.java

📚 Learning: 2026-01-02T19:23:29.698Z

Learnt from: karenyrx
Repo: opensearch-project/OpenSearch PR: 20335
File: modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/proto/request/search/SearchSourceBuilderProtoUtils.java:155-172
Timestamp: 2026-01-02T19:23:29.698Z
Learning: In the transport-grpc module, suggest and aggregations protos were removed from SearchRequestBody in protobufs 1.0.0 because they haven't been vetted for accuracy in the API specification. The URL parameter suggest support (suggest_field, suggest_mode, suggest_size, suggest_text) is a minimized subset and not intended as a replacement for full Suggester functionality.

Applied to files:

• CHANGELOG.md

📚 Learning: 2026-01-02T19:23:29.698Z

Learnt from: karenyrx
Repo: opensearch-project/OpenSearch PR: 20335
File: modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/proto/request/search/SearchSourceBuilderProtoUtils.java:155-172
Timestamp: 2026-01-02T19:23:29.698Z
Learning: The gRPC search API in OpenSearch is marked as "experimental" in official documentation, so changes to proto schemas that remove previously unsupported fields (those throwing UnsupportedOperationException) are not considered breaking changes.

Applied to files:

• CHANGELOG.md

🧬 Code graph analysis (2)

modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java (1)

server/src/main/java/org/opensearch/threadpool/ForkJoinPoolExecutorBuilder.java (1)

• ForkJoinPoolExecutorBuilder (31-147)

modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/GrpcPlugin.java (1)

server/src/main/java/org/opensearch/threadpool/ForkJoinPoolExecutorBuilder.java (1)

• ForkJoinPoolExecutorBuilder (31-147)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: gradle-check
• GitHub Check: Mend Security Check

🔇 Additional comments (9)

modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/GrpcPlugin.java (3)

31-31: LGTM!

Import correctly updated to ForkJoinPoolExecutorBuilder.

---

299-300: LGTM!

Javadoc accurately documents the rationale for using ForkJoinPool (work-stealing and better load balancing).

---

305-309: LGTM!

The migration to ForkJoinPoolExecutorBuilder is correctly implemented:

• Variable appropriately renamed to parallelism to match the ForkJoinPool terminology.
• Constructor call matches the ForkJoinPoolExecutorBuilder(name, parallelism, prefix) signature.
• Reuses the existing SETTING_GRPC_EXECUTOR_COUNT setting which is appropriate since it still controls the level of parallelism.

modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/ssl/SecureNetty4GrpcServerTransportTests.java (2)

16-16: LGTM!

Import correctly updated to ForkJoinPoolExecutorBuilder.

---

52-54: LGTM!

Test correctly updated to use ForkJoinPoolExecutorBuilder with matching constructor signature. The parallelism value of 4 is appropriate for testing.

modules/transport-grpc/src/test/java/org/opensearch/transport/grpc/Netty4GrpcServerTransportTests.java (4)

19-19: LGTM!

Import correctly updated to ForkJoinPoolExecutorBuilder.

---

46-52: LGTM!

Test setup correctly updated to use ForkJoinPoolExecutorBuilder with the same parallelism value (4) as the secure transport tests, ensuring consistency across test suites.

---

239-241: LGTM!

Comments appropriately updated to reflect that ForkJoinPool encapsulates thread management differently and the executor is managed by OpenSearch's ThreadPool system.

Also applies to: 257-258, 297-298

---

365-366: LGTM!

Test comments consistently updated throughout to reflect the new ForkJoinPool-based executor behavior.

Also applies to: 470-471, 486-487

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[github-actions]

❌ Gradle check result for a81020d: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for a81020d: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?