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Performance

Benchmark on Apple Silicon (M-series, macOS aarch64). Nix measurements use warm nix store cache. All times are median of 3 runs unless noted.

Environment

Mode Runtime Shell / Node.js
local Host macOS bash 3.2.57, Node v24.12.0
nix-packages nix develop wrapper bash 5.3.9, Node v24.14.0
apple-container Apple container (Linux VM) BusyBox ash 1.36.1, Node v20.20.2 (alpine)

Startup overhead

Measured with 1 job, 1 step (echo ok). This is the minimum time actrun takes before any user code runs.

Mode Startup
local ~0.13s
nix-packages ~0.70s
apple-container ~0.93s
  • nix-packages overhead comes from nix develop shell initialization, not package downloads (warm cache)
  • apple-container overhead comes from container lifecycle: create, start, exec, stop

Workspace modes

Measured with 2 jobs, 7 steps, light file I/O (mkdir, echo, wc, sort, sha256sum).

Mode Time
local ~0.27s
worktree ~0.26s
tmp ~0.60s
  • local and worktree are effectively the same speed
  • tmp adds ~0.3s for git clone into a temporary directory

CPU benchmark

Node.js prime sieve to 5,000,000 (trial division). Measures pure V8 compute with no I/O.

Mode V8 exec actrun total Overhead
local 644ms 0.78s 0.14s
nix-packages 629ms 1.45s 0.82s
apple-container 502ms 1.43s 0.93s
  • V8 execution speed is comparable across all modes
  • apple-container V8 is slightly faster (Linux VM scheduling / memory layout differences)
  • The overhead column = actrun total - V8 exec, matches startup overhead

File I/O benchmark

Node.js fs module operations. Measures filesystem metadata and data throughput.

Operation local nix-packages apple-container
Write 1,000 small files 52ms 47ms 14ms
Read 1,000 small files 12ms 10ms 4ms
Write 10MB sequential 1ms 1ms 3ms
Read 10MB sequential 1ms 2ms 3ms
Stat 1,000 files 3ms 2ms 2ms

Analysis

Many-file operations (write/read 1k files): apple-container is 3-4x faster than macOS native. This is due to ext4 vs APFS metadata performance — creating and opening many small files involves directory entry allocation and inode creation, where ext4 (even inside a VM) significantly outperforms APFS.

Large sequential I/O (10MB): All modes are comparable (~1-3ms). Block-level throughput is not a bottleneck at this scale.

local vs nix-packages: Identical I/O performance. Nix wraps the shell but does not change the filesystem path — all operations hit the same APFS volume.

Recommendations

Use case Recommended mode
Fast iteration / development local (0.13s startup)
Reproducible environment nix-packages (+0.6s startup)
CI-like isolation worktree (~0.26s)
Heavy file I/O (npm install, etc.) apple-container (3-4x faster metadata ops)
Production CI parity apple-container (matches Linux CI environment)