Apache Flink

Author: Ludovic HENRY ludovic.henry@qti.qualcomm.com
Date: 2026-06-17
Scope: RISC-V (riscv64/linux) support status for Apache Flink
Audience: Technical leadership, resource allocation strategy
Verification policy: Every claim is cross-referenced to a primary upstream source. Items that could not be verified against a second source are marked [NEEDS VERIFICATION].

1. Project Overview

Apache Flink is a distributed stream and batch processing framework, originally developed at TU Berlin and donated to the Apache Software Foundation in 2014. It is a top-level ASF project licensed under Apache License v2.0.

  • Repository: apache/flink
  • Homepage: flink.apache.org
  • Language breakdown: 87.5% Java, 8.0% Scala, 2.8% Python, 0.5% Shell, 0.4% TypeScript. No C, C++, or Assembly.
  • Build system: Apache Maven 3.8.6+
  • Primary deployment model: JVM-based distributed cluster (JobManager + TaskManagers)

Flink is architecturally a JVM project. All core runtime logic is JVM bytecode. Architecture-specific behavior surfaces only in optional native subsystems: the RocksDB/ForSt JNI state backend, Netty native transports, and PyFlink Cython extensions.

Governance: Standard ASF PMC meritocracy. Key decisions made on the dev@flink.apache.org mailing list. Major interface changes require a FLIP (Flink Improvement Proposal) process: DISCUSS thread, then VOTE thread requiring PMC consensus. A pure JVM project adding RISC-V support would not require a FLIP unless it affected public interfaces.

Corporate sponsors: Confluent is the dominant PMC presence (Robert Metzger as chair, Timo Walther, Fabian Hueske, Matthias Pohl, Martijn Visser). Alibaba/Ververica holds significant representation (Dian Fu, Jark Wu). Immerok was acquired by Confluent; its engineers are now on the Confluent PMC roster. Apache Flink is not a RISE project member and has no RISE project funding or blog coverage.

2. Port History and Upstreaming Timeline

The RISC-V porting history for Apache Flink is minimal and concentrated in a single 48-hour window in August 2025, with one earlier abandoned attempt.

February 2021 – abandoned attempt

PR #14934 was submitted by contributor advancedwebdeveloper, proposing to upgrade os-maven-plugin from 1.7.0 to address riscv64 build failures. Testing was performed on a SiFive U54-MC based board. The PR CI passed. The PR was silently closed after the automated bot flagged a missing JIRA ID in the title, and the author’s follow-up question (“@rmetzger, what’s next?”) went unanswered. No committer engaged. The fix lay dormant for 4.5 years.

August 1-2, 2025 – only landed RISC-V work

Contributor Gong Xiaofei (GitHub: Felix-Gong) filed FLINK-38178, an umbrella tracking issue for comprehensive RISC-V support, and immediately filed sub-task FLINK-38179 covering the same build failure that had blocked the 2021 attempt.

  • PR #26852 was submitted July 31, 2025 and closed August 1, 2025 by the author after committer snuyanzin requested that the title follow Flink’s JIRA-prefixed naming convention.
  • PR #26860 was submitted August 1, 2025 and merged August 2, 2025 by Sergey Nuyanzin (snuyanzin). Merge commit: d0eb9ef97908053a51df6b8e78c9a85ed9dc579b. Fix version: Flink 2.2.0.

The sole code change: one line in flink-formats/flink-parquet/pom.xml, upgrading kr.motd.maven:os-maven-plugin from version 1.7.0 to 1.7.1. Testing was performed on an SG2042-based RISC-V board; the contributor reported all tests passed [NEEDS VERIFICATION – no CI artifact or independent test run log is linked in the PR].

The umbrella issue FLINK-38178 remains open. No further sub-tasks have been filed since August 2025. The remaining scope of FLINK-38178 (CI coverage, documentation, performance optimizations, bug fixes) is entirely unstarted.

Summary timeline:

Date Event Status
Feb 2021 PR #14934: os-maven-plugin bump, SiFive U54-MC tested Abandoned, no committer engagement
Aug 1, 2025 FLINK-38178 umbrella filed; FLINK-38179 sub-task filed Open / Resolved
Aug 1, 2025 PR #26852 submitted Closed (naming convention)
Aug 2, 2025 PR #26860 merged; FLINK-38179 resolved Merged into master
Dec 4, 2025 Flink 2.2.0 released, containing the os-maven-plugin fix Released
Jun 2026 FLINK-38178 umbrella still open; no new sub-tasks Stalled

3. Upstream Support Tier

Apache Flink does not publish a formal platform tier document. There is no PLATFORMS.md, SUPPORT.md, OWNERS, or CODEOWNERS file in the repository that enumerates supported architectures or defines tier criteria.

The project’s CI runs exclusively on ubuntu-24.04 (x86_64). arm64 is not tested in CI either. There is no official tier policy to reference.

De facto tier classification for riscv64: Below any recognized tier. The architecture is not tested, not released, and not documented. The single merged work item is a build-system fix that prevents an immediate error during compilation – it does not constitute functional validation.

4. Technical Architecture and RISC-V-Specific Subsystems

Flink’s architecture has three layers with distinct riscv64 implications.

Layer 1 – JVM core (architecture-neutral)

All Flink runtime code (JobManager, TaskManager, scheduler, checkpoint coordinator, network stack coordination, SQL/Table API) is JVM bytecode. A GitHub file finder search for riscv in the apache/flink repository returned no matching files. A search for native likewise returned zero hits. There are no .c, .cpp, .h, or .S files anywhere in the repository tree. This layer runs on any riscv64 JVM without modification.

Layer 2 – JNI native subsystems (architecture-specific, critical gap)

RocksDB / ForSt state backend: Flink’s EmbeddedRocksDBStateBackend depends on com.ververica:frocksdbjni:8.10.0-ververica-1.0 and com.ververica:forstjni:0.1.8. These are fat JARs bundling pre-compiled .so files for: linux-x86_64, linux-aarch64 (glibc and musl), macOS x86_64, macOS arm64, and Windows x64. The upstream source repository (ververica/ForSt) has no riscv64 build targets – a file finder search for riscv returns no results. No riscv64 .so is bundled. At runtime on riscv64, loading this backend triggers UnsatisfiedLinkError. The only fallback is HashMapStateBackend, which is heap-resident and does not support incremental checkpointing or memory-managed state.

Netty native transport: Flink uses flink-shaded-netty (Netty 4.2.x). Netty’s native epoll and io_uring transports bundle x86_64 and aarch64 .so files; riscv64 native transport does not exist as a published artifact upstream as of mid-2026. Flink falls back automatically to NIO (pure Java) when native transport is unavailable. This is a performance degradation, not a functional failure.

Netty tcnative: flink-shaded-netty-tcnative-dynamic (test scope) provides BoringSSL JNI for TLS offload. No riscv64 artifact exists. Flink falls back to JDK JSSE. Test-scope only; not a runtime blocker.

Layer 3 – Python native extensions (architecture-specific, partial gap)

PyFlink (flink-python) includes 7 Cython .pyx extensions. These contain no hand-written SIMD or architecture guards – they are portable Cython that compiles to C and then to native code for the host architecture. PyPI wheels exist only for x86_64 Linux and macOS arm64. No riscv64 wheel is published. On riscv64, pip attempts a source build (requires Cython to be installed); if Cython is unavailable, execution falls back to pure Python.

5. Build System, Cross-Compilation, and Toolchain

Apache Flink is a Maven-only project. There is no CMake, no Makefile, no Cargo.toml, no go.mod, no cross-compilation toolchain files, no cmake/riscv64.cmake, no Dockerfile.riscv64, and no QEMU usage in the build pipeline (QEMU is used only in Docker image publishing, and only for amd64/arm64 targets).

The riscv64 build-system fix (FLINK-38179):

The flink-parquet submodule uses protobuf-maven-plugin, which relies on ${os.detected.classifier} (injected by os-maven-plugin) to download the correct pre-built protoc binary from Maven Central. Before Flink 2.2.0, os-maven-plugin 1.7.0 produced "os.detected.arch: unknown" and "org.apache.maven.MavenExecutionException: unknown os.arch: riscv" on riscv64 hosts, aborting the build. The upgrade to os-maven-plugin 1.7.1 in PR #26860 resolves this detection failure.

However, the fix surfaces a secondary blocker: with riscv64 now correctly detected, os.detected.classifier resolves to linux-riscv64, and protobuf-maven-plugin attempts to download com.google.protobuf:protoc:linux-riscv64 from Maven Central. No such binary artifact exists on Maven Central (protocolbuffers/protobuf#17798, open, untriaged as of mid-2026). A full mvn compile on a riscv64 host therefore still fails at the protoc download step unless protoc is pre-installed to the system PATH and the Maven plugin is configured to use it.

Standard build commands (for reference on riscv64 with protoc pre-installed):

mvn clean install -DskipTests
mvn clean install -DskipTests -Dfast -Pskip-webui-build -T 1C

Docker images: Official apache/flink images on Docker Hub target linux/amd64 and linux/arm64/v8 only. The flink-docker build pipeline uses docker/setup-qemu-action + docker/setup-buildx-action with a bake file listing only "linux/amd64" and "linux/arm64/v8". The CI build image (apache/flink-ci-docker:java_8_11_17_21_25_maven_386_jammy) is linux/amd64 only. No riscv64 Docker image exists.

6. Feature Coverage and Gap Analysis vs arm64 and amd64

Feature amd64 arm64 riscv64 Gap severity
JVM core runtime Full Full Full None
RocksDB/ForSt JNI state backend Full Full Missing (UnsatisfiedLinkError) Critical
ForSt JNI state backend Full Full Missing Critical
Maven build (os-maven-plugin) Full Full Fixed in 2.2.0 Fixed
Maven build (protoc binary) Full Full Missing on Maven Central Build blocker
Netty native epoll/io_uring Full Full Missing (NIO fallback) Performance
Netty tcnative / BoringSSL Full Full Missing (JSSE fallback) Minor
PyFlink wheels on PyPI Full Partial (macOS only) Missing (source-buildable) Gap
LZ4 JNI compression Full Full Missing (pure-Java fallback; repo archived) Performance
Conscrypt TLS provider Full Full Missing (JSSE fallback) Minor
Official Docker image Full Full Missing Gap
CI test coverage Full None None Missing
HDFS connector (Hadoop 2.10.2) Full Full Pre-dates riscv64 work Gap (use Hadoop 3.5.0+)
Published benchmarks Exists Exists None Data not available

RocksDB/ForSt JNI gap – operational impact: Stateful Flink applications using EmbeddedRocksDBStateBackend (the default for production large-state workloads) will fail at runtime on riscv64 with UnsatisfiedLinkError. The fallback HashMapStateBackend holds all state in JVM heap, which is functionally incompatible with large-state streaming jobs. This is the single most impactful gap for production use.

LZ4 gap – operational impact: The lz4-java library’s riscv64 JNI binding was never released. PR #212 was submitted to add riscv64 support but was never reviewed or merged. The repository was archived on December 2, 2025 and is now read-only; there is no upstream path to land this fix. Flink’s LZ4 shuffle compression falls back to the pure-Java implementation, which carries an estimated 3-5x throughput penalty [NEEDS VERIFICATION – no benchmark cited in research findings; figure is from the research synthesis, not a primary source].

Protoc build blocker – developer impact: The riscv64 protoc binary does not exist on Maven Central. Building Flink from source on a riscv64 host requires installing a system protoc and configuring the Maven plugin to use it, or cross-building. This is a non-trivial barrier for contributors working natively on riscv64 hardware.

7. CI/CD Infrastructure

Current state: zero riscv64 test coverage.

All Apache Flink CI runs on ubuntu-24.04 (x86_64) GitHub Actions runners using the apache/flink-ci-docker:java_8_11_17_21_25_maven_386_jammy Docker image. The following workflow files were inspected directly from the apache/flink master branch and confirmed to contain zero references to “riscv”:

  • .github/workflows/ci.yml (49 lines)
  • .github/workflows/template.flink-ci.yml (448 lines)
  • .github/workflows/template.pre-compile-checks.yml (77 lines)
  • .github/workflows/nightly.yml (127 lines)
  • .github/workflows/nightly-trigger.yml
  • .github/workflows/community-review.yml
  • .github/workflows/stale.yml
  • .github/workflows/docs.yml
  • .github/workflows/docs-legacy.yml

The nightly.yml workflow builds PyFlink wheels using cibuildwheel. No CIBW_ARCHS override is set, meaning cibuildwheel targets only the default x86_64 on ubuntu-latest. No QEMU setup step exists in this workflow. No riscv64 wheel is produced.

.gitlab-ci.yml, .cirrus.yml, and Jenkinsfile do not exist in the repository (HTTP 404 for all three).

No self-hosted riscv64 runners are registered. No QEMU-based emulation targets riscv64 anywhere in the CI configuration.

Consequence: Every merged change, including the os-maven-plugin fix in PR #26860, goes unvalidated on riscv64 hardware in upstream CI. The contributor’s manual test on an SG2042 board is the only validation record.

8. Distribution and Release Status

Primary Flink distribution (JVM tarballs via ASF mirrors):

Apache Flink publishes zero GitHub Releases. All releases are distributed as JVM bytecode tarballs (e.g., flink-2.2.1-bin-scala_2.12.tgz) via Apache Software Foundation mirrors. JVM bytecode is architecture-neutral and runs on any riscv64 JVM. However, as documented in Section 6, the embedded native libraries within these tarballs (RocksDB/ForSt JNI) do not include riscv64 binaries.

PyPI – apache-flink:

The latest release (2.3.0) publishes 13 files to PyPI. All were enumerated from the PyPI JSON API. The complete list covers: cp39/cp310/cp311/cp312 x macosx_10_9_x86_64, macosx_11_0_arm64, manylinux_*_x86_64, plus one source .tar.gz. No file contains “riscv64”. Linux wheels are published for x86_64 only.

Ubuntu Noble (24.04): Apache Flink is not packaged. The Ubuntu Noble package search for “flink” returns only cufflinks (bioinformatics) and python3-reflink (filesystem). Apache Flink does not exist as an Ubuntu package under any architecture.

Debian: tracker.debian.org/pkg/apache-flink returns HTTP 404. Apache Flink is not packaged in Debian.

Arch Linux RISC-V: Apache Flink does not appear in the Arch RISC-V port status page (archriscv.felixc.at).

Docker Hub (apache/flink): Images for Flink 2.0.x, 2.1.x, 2.2.x are published with Java 11/17/21 variants. Architectures: linux/amd64, linux/arm64/v8 only. No linux/riscv64 manifest exists.

RISE wheel builder: The RISE project GitLab wheel builder (riseproject.gitlab.io/python/wheel_builder) does not list apache-flink. The GitLab PyPI endpoint for apache-flink redirects (HTTP 302) to PyPI, returning the same x86_64-only results.

9. Dependencies

The following table covers dependencies with JIT backends, SIMD paths, native code, JNI bindings, compression, crypto, or memory allocation.

Dependency Role riscv64 Build riscv64 Release Blocking Issues
OpenJDK (JVM runtime) Required to run all Flink code Builds (cross-compile CI only; no full HotSpot CI job on riscv64) Temurin 21/17/11 available from Adoptium; not Tier 1 C2 JIT missing several intrinsics; no riscv64 jtreg CI. See project-reports/openjdk.md
snappy-java 1.1.10.7 Snappy compression for state/shuffle riscv64 native .so bundled since 1.1.10.0 (PR #396, merged 2023) riscv64 artifact present in releases >= 1.1.10.0; Flink uses 1.1.10.7 None. Fully supported.
lz4-java (archived) LZ4 compression for shuffle and state riscv64 JNI binding never released; PR #212 open and unreviewed No riscv64 release; repository archived December 2, 2025 (read-only) Permanent gap: repo archived, no path to merge PR #212. Pure-Java fallback exists but with significant performance penalty.
Netty 4.2.13.Final Network transport (RPC, checkpointing, REST) riscv64 native epoll + io_uring built and shipped since 4.1.103.Final (PR #13670, merged Dec 2023) riscv64 epoll + io_uring artifacts present in releases >= 4.1.103.Final No open blocking issues for epoll/io_uring. tcnative (TLS) has no riscv64 artifact (see below).
netty-tcnative (test scope) TLS offload via BoringSSL Not built for riscv64 No riscv64 artifact; no issues or PRs filed Test scope only; JSSE fallback is functional. Not a runtime blocker.
frocksdbjni 8.10.0-ververica-1.0 RocksDB state backend JNI Not built for riscv64; no riscv64 targets in CircleCI build config No riscv64 artifact published Runtime blocker for EmbeddedRocksDBStateBackend: UnsatisfiedLinkError on riscv64. Must fall back to HashMapStateBackend.
forstjni 0.1.8 ForSt state backend JNI Not built for riscv64; same ververica/ForSt source; file finder search for riscv returns no results No riscv64 artifact published Runtime blocker for ForSt state backend: same as frocksdbjni.
Apache Arrow 19.0.0 (arrow-vector, arrow-memory-netty) Python/Flink data exchange; flink-python Arrow-based batch Arrow Java is JVM bytecode (architecture-neutral). Arrow C++ builds on riscv64 but has riscv64 test failures (PR #49556, open draft). Arrow Java JARs are architecture-neutral; run on any JVM. No riscv64 PyArrow wheel on PyPI. PyArrow wheel gap affects flink-python users; must build from source (~1 hour). Arrow C++ test failures on riscv64 (PR #49556 open).
protoc 4.32.1 (build-time) Proto code generation at build time No pre-built riscv64 protoc binary on Maven Central (protocolbuffers/protobuf#17798, open, untriaged) No riscv64 protoc binary on Maven Central Build blocker: mvn compile on riscv64 fails at protoc download unless protoc is pre-installed to PATH.
os-maven-plugin 1.7.1 Maven build-time arch/OS detection Correctly maps riscv64 as of 1.7.1; Flink upgraded in PR #26860 (Flink 2.2.0) 1.7.1 released; Flink uses it Was broken before Flink 2.2.0. Fixed.
Apache Hadoop 2.10.2 (provided scope) HDFS file system connector Hadoop 2.10.2 predates all riscv64 work No riscv64 artifacts for 2.10.2 Users requiring HDFS must use Hadoop 3.5.0+ (unreleased as of research). ISA-L erasure coding degrades to Java fallback. See project-reports/apache-hadoop.md
Apache Parquet (parquet-hadoop, parquet-avro) Columnar format read/write Java-only Architecture-neutral JARs None. Pure Java.
Apache Avro 1.11.5 Schema-based serialization Java-only Architecture-neutral JARs None.
Conscrypt 2.5.1 (runtime scope in flink-python) Alternate TLS/crypto provider No riscv64 support; latest release added linux-aarch64 (2.6-alpha3); riscv64 not mentioned; zero issues or PRs filed in google/conscrypt for riscv64 No riscv64 artifact Runtime scope; JSSE fallback is functional.
Byte Buddy 1.17.6 Runtime bytecode generation for serializers JVM bytecode only, ASM-based, no native code Architecture-neutral None.
Janino (flink-table-runtime) Runtime Java compilation for SQL codegen JVM bytecode only Architecture-neutral None.
Kryo 5.6.2 Fallback Java object serialization JVM bytecode only (uses Unsafe; no arch-specific path) Architecture-neutral None.
ZooKeeper (flink-shaded-zookeeper-3:3.7.2) Leader election, HA coordination Java-only Architecture-neutral None.

Blocking issues summary:

Severity Dependency Issue
Build blocker protoc 4.32.1 No riscv64 binary on Maven Central; #17798 open, untriaged
Runtime blocker frocksdbjni / forstjni No riscv64 .so; EmbeddedRocksDBStateBackend and ForSt backend unusable on riscv64
Permanent performance gap lz4-java PR #212 unmerged; repo archived Dec 2025; no upstream resolution path
TLS performance gap netty-tcnative No riscv64 BoringSSL JNI; falls back to JSSE
HDFS compatibility Hadoop 2.10.2 Predates riscv64 work; HDFS users must use Hadoop 3.5.0+
PyFlink gap PyArrow No riscv64 wheel; source build required (~1 hour); Arrow C++ has riscv64 test failures

10. Ecosystem Status

RISE project: Apache Flink is not a RISE project member. All 27 published RISE blog posts (May 2024 through June 2026) were examined; none mention Apache Flink. The RISE wheel builder does not list apache-flink among its riscv64 wheel packages. No RISE funding or engineering engagement with the Flink project exists in the public record.

RISE member companies and Flink PMC overlap: Alibaba (DAMO Academy is a RISE Premier Member) has engineers on the Flink PMC (Dian Fu, Jark Wu) and in the contributor base. However, no riscv64-specific contributions from Alibaba/DAMO Academy have appeared in the Flink repository.

Contributor activity: The entire riscv64 work in the Flink repository originates from a single contributor, Gong Xiaofei (Felix-Gong). No committer or PMC member has self-assigned to riscv64 work beyond the single review/merge of PR #26860 by Sergey Nuyanzin.

Broader RISC-V ecosystem: Netty native epoll/io_uring for riscv64 was added in Netty 4.1.103.Final (merged December 2023), which is relevant to Flink’s network transport layer. snappy-java has full riscv64 support since 1.1.10.0 (2023). The lz4-java gap is permanent due to archival. The critical ververica/ForSt JNI gap has no current upstream activity.

Hardware tested: The only documented Flink-on-riscv64 validation was performed on an SG2042-based board (SpacemiT/Sophon SG2042, a 64-core RISC-V server processor) by the contributor in August 2025. No independent validation exists.

11. Known Bugs and Active Issues

RISC-V-specific issues:

FLINK-38178 – “RISC-V Architecture Support in Apache Flink” (umbrella)

  • Status: Open, unresolved, no fix version, no assignee, no comments
  • Created: August 1, 2025 by Gong Xiaofei
  • Scope: (1) platform-specific optimizations/compatibility, (2) post-implementation bug fixes, (3) test/CI coverage for RISC-V, (4) documentation updates
  • Sub-tasks: FLINK-38179 (resolved); all other sub-areas have zero sub-tasks filed
  • Assessment: The umbrella has been dormant since August 2025. With no new sub-tasks, no assignee, and no committer engagement, it is a placeholder, not an active workstream.

FLINK-38179 – “Build Failure Due to os-maven-plugin Missing Support”

  • Status: Resolved, Fix Version 2.2.0
  • Root cause: os-maven-plugin 1.7.0 did not recognize riscv64; error: "os.detected.arch: unknown" / "org.apache.maven.MavenExecutionException: unknown os.arch: riscv"
  • Fix: os-maven-plugin upgraded to 1.7.1 in flink-formats/flink-parquet/pom.xml

Earlier RISC-V-adjacent issue:

FLINK-21139 – “ThresholdMeterTest.testMarkMultipleEvents unstable”

  • Status: Fixed in Flink 1.13.0 (February 2021)
  • First reported from a riscv64 environment (SiFive Rocket, Debian, OpenJ9 JVM with JIT disabled)
  • Root cause was general test timing flakiness, not riscv64-specific. Fixed as a general correctness issue.

Active correctness bug (cross-platform, relevant to riscv64 workloads):

FLINK-39677 – “ARRAY_SORT Comparator Contract Violation”

  • Status: Open, Major priority
  • Affected versions: 1.20.4, 2.0.2, 2.1.2, 2.2.1, 2.3.0
  • Root cause: ArraySortComparator.compare violates the Java Comparator antisymmetry contract – both compare(a,b) and compare(b,a) return -1 for equal elements. TimSort throws "Comparison method violates its general contract!" on arrays of 32 or more elements containing duplicates.
  • Relevance to riscv64: NaN and floating-point comparisons trigger this pattern (NaN comparisons are never equal under >), making this a correctness hazard for any floating-point analytical workload. Applies equally to riscv64.
  • Open PRs: #28155, #28159
  • Reported: May 13, 2026

Published RISC-V benchmarks: Data not available. No throughput, latency, or comparative performance figures for Apache Flink on riscv64 exist in any public source – not on the Flink blog, the RISE blog, Apache JIRA, or GitHub as of mid-2026.

12. Objections and Upstream Blockers

Objection: “The build fix is already merged; Flink 2.2.0 supports riscv64.”

Refuted. The merged change (PR #26860) is a one-line pom.xml version bump for a Maven plugin. It removes one build-time error while immediately exposing a second build-time error (missing protoc binary for riscv64 on Maven Central). It does not validate that any native component compiles or passes tests on riscv64. No CI validates riscv64. The RocksDB/ForSt JNI state backend – the component that distinguishes production stateful Flink from a prototype – has no riscv64 native library and fails with UnsatisfiedLinkError on any riscv64 host. Characterizing Flink 2.2.0 as “supporting riscv64” overstates the situation by a significant margin.

Blocker 1 – frocksdbjni / forstjni (no riscv64 build):

This is controlled by Ververica (Alibaba subsidiary). The build pipeline is CircleCI-based and enumerates its targets explicitly. riscv64 is absent. Adding riscv64 requires Ververica to allocate engineering time, a riscv64 build environment, and a CI runner. This is an external dependency that Flink contributors cannot resolve unilaterally. No riscv64 request or issue has been filed against the ververica/ForSt repository.

Blocker 2 – protoc riscv64 binary on Maven Central:

protocolbuffers/protobuf#17798 is open and untriaged as of mid-2026. This is a Google-owned project. The Flink community has no leverage here. The workaround (pre-install protoc to PATH) is documented in principle but not in Flink’s official build documentation.

Blocker 3 – lz4-java (permanently archived):

The lz4/lz4-java repository was archived December 2, 2025. It is read-only. PR #212 adding riscv64 support is permanently unmerged with no path forward. The pure-Java LZ4 fallback is the only available option. Flink would need to either fork lz4-java, vendor the native code, or replace the dependency.

Blocker 4 – no riscv64 CI:

Without CI, no regression guarantee exists for any future Flink change on riscv64. Every merge risks silent breakage. Adding riscv64 CI requires either QEMU-based emulation (slow, typically 10-20x for integer workloads) or access to physical riscv64 hardware or hosted CI (e.g., Scaleway, RISE Enablement WG resources). Neither option has been proposed or funded within the Flink project.

Blocker 5 – single-contributor ownership:

All riscv64 work originates from one external contributor (Gong Xiaofei) with no PMC sponsor, no committer assigned, and no corporate backer identified in the public record. The umbrella FLINK-38178 has received zero engagement since its creation in August 2025. The project has no organizational commitment to riscv64 support.

13. Investment Analysis

13.1 Functional Enablement

The highest-priority gap for functional riscv64 support is the RocksDB/ForSt JNI state backend. Production stateful streaming jobs (exactly-once, large state, incremental checkpoints) require this component. Without it, Flink on riscv64 is limited to stateless or small-state workloads using heap-based state.

The ForSt/RocksDB JNI fix requires:

  • An riscv64 build environment with C++ toolchain targeting riscv64
  • CMake configuration within the RocksDB build system for riscv64 (RocksDB upstream supports riscv64 in source; ververica’s fork inherits this)
  • Adding riscv64 as a CI target in the ververica/ForSt CircleCI pipeline
  • Publishing the fat JAR with the riscv64 .so included
  • This work must be done by or in coordination with Ververica; it cannot be done unilaterally within the apache/flink repository

Separately, the protoc build blocker requires either contributing a riscv64 protoc binary to Maven Central (upstream in protocolbuffers/protobuf) or documenting and automating the PATH-based workaround in Flink’s build docs. The former is a multi-month effort requiring Google engagement; the latter is a 1-2 day documentation task.

13.2 Performance Optimization

Flink’s JVM core has no SIMD or architecture-specific code paths. Performance optimization on riscv64 is entirely a function of:

  1. JVM quality (HotSpot C2 JIT, intrinsics) – upstream OpenJDK, not Flink
  2. Native library performance (RocksDB, Netty epoll) – upstream dependencies, not Flink
  3. Memory allocation patterns (off-heap via Netty; on-heap via JVM)

There is no Flink-specific SIMD or RVV optimization work to be done within the apache/flink repository. Any RISC-V performance investment for Flink flows through OpenJDK and the native dependency layer.

The lz4-java archival creates a permanent ~3-5x LZ4 compression throughput gap [NEEDS VERIFICATION – no primary source benchmark found]. The practical mitigation is using Snappy (fully supported on riscv64) instead of LZ4 for shuffle and state compression, at the cost of slightly lower compression ratios.

13.3 CI/CD Infrastructure

Adding riscv64 CI to Flink requires:

  • A GitHub Actions runner with riscv64 capability, or QEMU-based emulation on existing ubuntu-24.04 runners
  • A Flink CI Docker image built for linux/riscv64 (requires adding riscv64 to flink-docker bake file)
  • A new CI workflow job (or extension of template.flink-ci.yml) that runs the Flink test suite on riscv64
  • Significant compute time: Flink’s full test suite is multi-hour on x86_64; QEMU emulation would multiply this by 10-20x

RISE Enablement WG has infrastructure (Scaleway riscv64 instances) that has been used for other Java projects (OpenJDK). Engagement with RISE to add Flink to that infrastructure is a plausible path, but requires RISE buy-in and a Flink committer willing to maintain the CI configuration.

13.4 Ecosystem Enablement

  • PyFlink riscv64 wheel: Requires adding riscv64 to the nightly.yml cibuildwheel configuration and providing a QEMU setup step. This is a moderate effort (1-2 weeks) and requires PyArrow riscv64 wheel availability as a prerequisite, which itself is blocked by the Arrow C++ riscv64 test failures (PR #49556, open draft).
  • Official Docker image: Requires adding linux/riscv64 to the flink-docker bake file and a base JDK image for riscv64. Eclipse Temurin riscv64 images exist for JDK 17/21. This is a low effort (1-2 days) configuration change, contingent on the RocksDB JNI gap being resolved (otherwise the image is incomplete).
  • Documentation: FLINK-38178 scope item 4. Low effort (1-2 days) once the functional gaps are resolved.
  • HDFS connector: Users with HDFS must use Hadoop 3.5.0+. Flink should document this requirement. Low effort.

13.5 Summary Table

Area Work Item Effort (person-weeks) Owner Priority
Functional RocksDB/ForSt JNI riscv64 build (frocksdbjni/forstjni) 4-8 Ververica (external) Critical
Functional protoc riscv64 binary on Maven Central 8-16 Google/protocolbuffers (external) High
Functional Workaround: document PATH-based protoc on riscv64 in Flink build docs 0.25 Flink contributor High
Functional lz4-java replacement or fork for riscv64 JNI 4-6 TBD (lz4-java archived) Medium
Functional Document HashMapStateBackend fallback and Snappy-vs-LZ4 tradeoffs for riscv64 0.5 Flink contributor Medium
CI/CD riscv64 CI runner integration (RISE Scaleway or QEMU) 3-5 Flink committer + RISE WG High
CI/CD riscv64 CI Docker image for apache/flink-ci-docker 1-2 Flink committer High
CI/CD File riscv64 CI sub-task under FLINK-38178 and drive to completion 0.5 Flink contributor High
Ecosystem PyFlink riscv64 wheel (cibuildwheel + QEMU) 2-3 Flink contributor; blocked on PyArrow Medium
Ecosystem Official apache/flink Docker image for linux/riscv64 0.5 Flink committer Medium
Ecosystem Hadoop 3.5.0+ compatibility documentation for HDFS on riscv64 0.25 Flink contributor Low
Performance JVM JIT/intrinsics improvement for riscv64 N/A (OpenJDK scope) OpenJDK upstream N/A
Performance Netty native epoll for riscv64 (epoll already available from 4.1.103.Final) 0 (already merged upstream) None Done

14. Updates

No updates yet – initial report dated 2026-06-17.

15. References