Node.js Pointer Compression Experiments

This repository contains experiments for building Node.js with V8 pointer compression enabled. Pointer compression is a V8 optimization that reduces memory usage by using 32-bit compressed pointers instead of full 64-bit pointers.

Docker Images

Pre-built multi-architecture images (amd64/arm64) are available on DockerHub:

# Pull the latest image (Debian bookworm, recommended)
docker pull platformatic/node-caged:latest

# Or use a specific variant
docker pull platformatic/node-caged:bookworm  # Full Debian
docker pull platformatic/node-caged:slim      # Minimal Debian
docker pull platformatic/node-caged:alpine    # Alpine Linux (experimental)

# Pin to a major Node.js version (recommended for most users)
docker pull platformatic/node-caged:25
docker pull platformatic/node-caged:25-slim
docker pull platformatic/node-caged:25-alpine

# Pin to an exact Node.js version
docker pull platformatic/node-caged:25.6.1
docker pull platformatic/node-caged:25.6.1-slim

Available Tags

Tag	Description
latest, bookworm	Latest build on Debian bookworm (recommended)
slim	Minimal Debian bookworm-slim runtime (~100MB smaller)
alpine	Alpine Linux with musl libc (smallest, experimental)
{major}	Latest patch of major version on bookworm (e.g., 25)
{major}-{variant}	Latest patch of major version with variant (e.g., 25-slim)
{version}	Exact Node.js version on bookworm (e.g., 25.6.1)
{version}-{variant}	Exact version and variant (e.g., 25.6.1-alpine)

Variant Comparison

Variant	Base Image	Size	Compatibility
bookworm	debian:bookworm	~250MB	Full glibc, best compatibility
slim	debian:bookworm-slim	~150MB	Minimal glibc runtime
alpine	alpine:3.21	~100MB	musl libc, experimental

Quick Start

Build the Docker image:

docker build --network=host -t node-pointer-compression .

Run the tests:

./run-tests.sh

Benchmark Results

Memory comparison between standard Node.js 22 and pointer-compressed Node.js 25 (with --expose-gc):

Data Structure	Standard Node 22	Pointer Compressed	Savings
Array of Objects (1M items)	40.47 MB (42.43 B/item)	20.24 MB (21.22 B/item)	50%
Nested Objects (500K items)	50.21 MB (105.29 B/item)	24.64 MB (51.68 B/item)	51%
Linked List (500K items)	19.08 MB (40.01 B/item)	9.54 MB (20.01 B/item)	50%
Array of Arrays (500K items)	38.76 MB (81.28 B/item)	19.38 MB (40.64 B/item)	50%

Key Findings

• Pointer compression delivers consistent ~50% memory reduction across all pointer-heavy data structures
• Bytes-per-item is almost exactly halved, matching the theoretical expectation (32-bit vs 64-bit pointers)
• Baseline memory usage is also lower (2.11 MB vs 3.74 MB)

Tradeoffs

• Heap limit: 4GB per V8 isolate. Each worker thread has its own 4GB limit, so you can exceed 4GB total using multiple workers (e.g., main + 4 workers = 20GB max)
• Compatibility: Requires building Node.js from source with --experimental-enable-pointer-compression

Native Addon Compatibility

N-API addons work correctly with pointer compression. Tested and verified:

Addon	Type	Status
bcrypt	N-API	✓ Works
sharp	N-API	✓ Works
@napi-rs/uuid	Rust N-API	✓ Works
@node-rs/argon2	Rust N-API	✓ Works

Non-N-API native addons may crash. Addons using the older V8 native addon API (like better-sqlite3) are not compatible with pointer compression and can segfault. Packages that rely on nan are especially affected. Always prefer N-API-based alternatives.

Workarounds for Non-N-API Addons

If your dependency uses nan and does not provide binaries built for this runtime, you must force a local rebuild of its native addon.

If the package in node_modules still contains source files, try a normal rebuild:

cd node_modules/<package-name>
pnpm install --ignore-scripts
pnpm run rebuild

Some packages on npm do not ship source files needed to rebuild. In these cases, you may need to fetch the source from the git repository, copy it back into node_modules, and run a manual rebuild.

Known affected package example

@datadog/pprof

This was tested against @datadog/pprof 5.13.5.

cd node_modules/@datadog/pprof
pnpm install --ignore-scripts
PPROF_VERSION=$(node -p "require('./package.json').version")
PPROF_REPO=$(node -p "require('./package.json').repository.url.replace('git+', '')")
git clone -q --depth=1 --branch=v$PPROF_VERSION $PPROF_REPO /tmp/pprof-nodejs > /dev/null 2>&1
mv /tmp/pprof-nodejs/{binding.gyp,bindings} .
rm -rf /tmp/pprof-nodejs
pnpm run rebuild
cd ../../..

How It Works

The Dockerfile builds Node.js from the v25.x branch with the --experimental-enable-pointer-compression configure flag. This enables V8's pointer compression feature which uses 32-bit offsets from a base address instead of full 64-bit pointers.

Test Scripts

• tests/verify-pointer-compression.js - Verifies pointer compression is enabled by checking heap limits
• tests/memory-benchmark.js - Benchmarks memory usage with pointer-heavy data structures
• tests/worker-heap-limits.js - Verifies each worker thread has its own 4GB heap limit
• tests/napi-addon-test.js - Tests N-API native addon compatibility (requires npm install)

Building Locally

For local development, use the root Dockerfile:

# Build for local architecture
docker build --network=host -t node-pointer-compression .

# Run interactively
docker run -it node-pointer-compression

# Run a script
docker run -v $(pwd):/app node-pointer-compression node /app/your-script.js

To build a specific variant locally:

# Build bookworm variant
docker build -f docker/bookworm/Dockerfile -t node-pointer-compression:bookworm .

# Build slim variant
docker build -f docker/slim/Dockerfile -t node-pointer-compression:slim .

# Build alpine variant
docker build -f docker/alpine/Dockerfile -t node-pointer-compression:alpine .

CI/CD

The GitHub Actions workflow builds and publishes multi-architecture images:

• Trigger: Manual only (workflow_dispatch)
• Version detection: Automatically detects latest Node.js v25.x release
• Duplicate check: Skips build if version already exists on DockerHub
• Force rebuild: Option to bypass version check and rebuild

Images are built natively on both amd64 and arm64 runners for optimal build performance.