When Vitest Met 128GB of RAM (and Won). During testing, we observed how Vitest handled CPU overload, showcasing impressive performance under heavy computational stress.
The System That Screamed
There are moments in development when you can almost hear your computer sigh. Mine didn’t sigh. It screamed. Thirty-two CPU cores pinned to 100%, all 128GB of memory consumed, swap space overflowing like a dam giving way. Everything lagged: terminals stuttered, containers froze, browsers hung suspended in time. The crime scene? A single command: vitest run.
This wasn’t the crash of a reckless coder or the folly of bad syntax. It was the quiet, invisible default of a testing framework doing what it thought was best. Vitest, in its infinite optimism, spun up as many workers as I had CPU cores. Node, ever the willing accomplice, eagerly multiplied threads until my workstation looked like a mining rig in distress.
What I didn’t realize at the time was that every project I had open and there were six of them, was already barely ticking over in the background. Go servers, React builds, containerized services, and a couple of indexing pipelines. All this before Vitest decided to occupy every remaining thread like an uninvited guest.
When Everything Froze
Within seconds, my system was overwhelmed. The load average went into double digits, then triple. The machine was technically alive, but I was effectively locked out. I watched helplessly as htop showed a field of solid green bars. Swap space began to churn. Fans roared. It was a complete system seizure brought on not by a bug, but by efficiency taken too far.
It turned out that Node’s approach to concurrency is simple: if you don’t set boundaries, it assumes you want all of them. Vitest used every logical core available, launching independent V8 isolates for each test process. Each of those processes carried its own memory footprint, initialization overhead, and in my case, cryptographic and networking dependencies. Multiply that by thirty-two and you get an unintentional denial of service, self-inflicted and spectacular.
The Flag That Saved Me
The solution was laughably simple once I found it:
vitest --maxWorkers=8
That single flag restored peace to my digital universe. CPU usage dropped to something resembling sanity. Memory freed up. Swap drained. My system cooled down and responded again. The lesson? Automation without boundaries is chaos disguised as productivity.
It’s easy to assume more cores mean faster performance. It’s also wrong. Without coordination, parallelism can degrade performance instead of improving it. Each additional worker competes for shared resources: CPU cache, memory bandwidth, disk I/O. When everything runs at once, nothing truly runs well.
The Myth of More
This wasn’t just a technical failure, it was a philosophical one. In modern development, we equate scale with progress. We brag about how many threads, nodes, or containers we can run. But that kind of thinking misses the point. The power of computing lies in control, not excess.
No developer can know everything. Frameworks evolve, defaults change, and small oversights can become system-level disasters. The trick is not to master every tool but to understand the consequences of their defaults. Blind trust in software abstractions is how we end up with thirty-two cores burning just to prove a point.
Knowing When to Stop
If there’s a moral to this, it’s that restraint is a skill worth learning. Technology rewards speed, but wisdom demands limits. Just because we can run everything at once doesn’t mean we should. Sometimes, the most elegant optimization is to slow down.
When Vitest met 128GB of RAM, it didn’t just crash my machine, it reminded me of a simple truth. Progress is not about pushing every system to its edge. It’s about knowing when to stop.
Configuration Fix
The permanent fix came down to a single adjustment in my vitest.config.ts:
export default defineConfig({
test: {
maxWorkers: 8,
},
})
That change ensures no matter where I run tests, whether in CI, local, or container environments, they stay within safe CPU limits. It’s the guardrail I should have had from the start. The rest of the system now runs smoother, with all six active projects happily coexisting.
Have you ever pushed your system to its limits without meaning to? Share your story and pass this post along to anyone who’s learned a lesson the hard way. The more we share, the better we all build.
