Why vx is fast: five decisions, not a trick

With nothing changed, vx adds 799 ms to a 9,603-task run. No daemon
keeps it warm.

Time added over the ideal run, 1,601 projects, 9,603 tasks	vx	Turborepo	Nx	Vite Task
Nothing changed	799 ms	927 ms	24.15 s	12.07 s
Nothing changed, outputs restored	1.28 s	2.01 s	24.45 s	11.86 s
Cold build	7.57 s	9.63 s	3 min 6 s	9.01 s
Cold build: CPU the runner burns	36.64 s	1 min 12 s	5 min 34 s	25.32 s

Synthetic monorepo, 1,601 projects, 30 levels · linux x64, 4 cores, concurrency 10 · vx 0be036747, Turborepo 2.11.10, Nx 24.0.1, Vite Task (vite-plus) 1.4.0, native configs · 2026-10-23 · benchmarks

Five design choices make that number. Each one also makes the cache
harder to get wrong.

1. Git already hashed your files

This repo, 48 MB · linux x64, 4 cores, warm page cache · 2026-10-23

Git keeps a hash of every tracked file. vx asks git instead of reading
them. Clean-tree key derivation costs zero source-file reads.

A dirty file gets the same hash git would give it, so a commit never
changes a key (how).

2. The scheduler counts with bitsets

vx starts the task with the most work below it first. Counting that with
a graph walk took 8.5 s of a 10 s run on a 1,090-package graph.

Bitsets do it in milliseconds (how).

3. A hit on an up-to-date tree is a few stat calls

vx wipes outputs before a task runs, so it knows what a hit leaves on
disk. If each file still matches (size, mode, millisecond mtime, inode
and ctime), there is nothing to restore.

4. A hit is a file copy

The local cache stores plain files and the kernel copies them.

Metadata and the captured stdout live in the index (the stdout in a side
table), so the log comes back with one SQL read
(how).

5. Nothing runs that is not needed

A run reads .vx/projects.lock.json and evaluates no config. No
telemetry plugin means no listener and no git spawn. A plugin that
skips a task costs nothing.

Every change to this path ships with a measured before and after
(Optimizations). More at
vznjs.github.io/vx.

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Originally published on the vx blog. vx is open-source (MIT) task orchestration with a build cache: vznjs.github.io/vx · GitHub.

_{Written with AI assistance.}