SCache Configuration Documentation

Overview

This document records our sccache configuration for future reference. Sccache is currently disabled due to GitHub Actions cache service issues, but we plan to re-enable it once the service is stable.

Current Status

🚫 DISABLED - Temporarily disabled due to GitHub Actions cache service issues:

sccache: error: Server startup failed: cache storage failed to read: Unexpected (permanent) at read => <h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>

Planned Configuration

Environment Variables (setup-env action)

RUSTC_WRAPPER=sccache
SCCACHE_GHA_ENABLED=true
SCCACHE_CACHE_SIZE=2G  # For Docker builds

GitHub Actions Integration

Workflows Using sccache

code-quality.yml - Build caching for clippy and rustfmt
test-unit.yml - Build caching for unit tests
test-integration.yml - Build caching for integration tests

Action Configuration

- uses: mozilla-actions/sccache-action@v0.0.4

Expected Benefits

50%+ faster builds through compilation caching
Reduced CI costs by avoiding redundant compilation
Better developer experience with faster feedback loops

Performance Targets

Build cache hit rate: Target > 80%
Compilation time reduction: 50%+ on cache hits
Total CI time: Reduce by 10-20 minutes per run

Local Development Setup

For local development when sccache is working:

# Install sccache
cargo binstall sccache -y

# Set environment variables
export RUSTC_WRAPPER=sccache
export SCCACHE_GHA_ENABLED=true

# Check stats
sccache --show-stats

# Clear cache if needed
sccache --zero-stats

Re-enabling Steps

When GitHub Actions cache service is stable:

Re-enable in workflows:
- Uncomment mozilla-actions/sccache-action@v0.0.4 in workflows
- Restore sccache environment variables in setup-env action
Test with minimal workflow first:
- Start with code-quality.yml
- Monitor for cache service issues
- Gradually enable in other workflows
Monitor performance:
- Track build times before/after
- Monitor cache hit rates
- Watch for any new cache service errors

Configuration Locations

Files containing sccache configuration

.github/actions/setup-env/action.yml - Environment variables
.github/workflows/code-quality.yml - Action usage
.github/workflows/test-unit.yml - Action usage
.github/workflows/test-integration.yml - Action usage
docs/sccache-configuration.md - This documentation

Docker Integration

For Docker builds, pass sccache variables as build args:

build-args: |
  SCCACHE_GHA_ENABLED=true
  RUSTC_WRAPPER=sccache
  SCCACHE_CACHE_SIZE=2G

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