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## Problem
The indexed package importer always creates a staging temp directory, imports files there, then renames to the final location. For cold installs where the target doesn't exist (the common case), the staging + rename is unnecessary overhead.
## Solution
- **Fast path**: callers already verify the target package is missing before calling `importIndexedDir`, so we can write directly into the final directory and skip the temp dir + rename. Falls back to the atomic staging path on EEXIST (concurrent import race) or when `keepModulesDir` is set (hoisted linker needs to merge existing `node_modules`).
- **Completion marker**: `package.json` is written last by `tryImportIndexedDir`, so `pkgExistsAtTargetDir()` (which checks for `package.json`) won't consider a partially-imported directory as complete after a crash.
- **Atomic copy**: the copy import path (non-COW filesystems) uses a temp file + `renameOverwriteSync` for the `package.json` write, since `copyFileSync` is not atomic. Hard links and reflinks are inherently atomic. This is expressed via the `Importer` interface (`importFile` + `importFileAtomic`), passed as the first argument to `importIndexedDir`.
- **Synthetic package.json**: packages that lack a `package.json` (e.g. injected Bit workspace packages) now get a synthetic empty `{}` added to the store, so the completion marker works universally.
- **DRY**: extracted `retryWithSanitizedFilenames()` to deduplicate the ENOENT handler used by both the fast path and staging path.
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Fast, disk space efficient package manager:
- Fast. Up to 2x faster than the alternatives (see benchmark).
- Efficient. Files inside
node_modulesare linked from a single content-addressable storage. - Great for monorepos.
- Strict. A package can access only dependencies that are specified in its
package.json. - Deterministic. Has a lockfile called
pnpm-lock.yaml. - Works as a Node.js version manager. See pnpm env use.
- Works everywhere. Supports Windows, Linux, and macOS.
- Battle-tested. Used in production by teams of all sizes since 2016.
- See the full feature comparison with npm and Yarn.
To quote the Rush team:
Microsoft uses pnpm in Rush repos with hundreds of projects and hundreds of PRs per day, and we’ve found it to be very fast and reliable.
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Background
pnpm uses a content-addressable filesystem to store all files from all module directories on a disk. When using npm, if you have 100 projects using lodash, you will have 100 copies of lodash on disk. With pnpm, lodash will be stored in a content-addressable storage, so:
- If you depend on different versions of lodash, only the files that differ are added to the store.
If lodash has 100 files, and a new version has a change only in one of those files,
pnpm updatewill only add 1 new file to the storage. - All the files are saved in a single place on the disk. When packages are installed, their files are linked from that single place consuming no additional disk space. Linking is performed using either hard-links or reflinks (copy-on-write).
As a result, you save gigabytes of space on your disk and you have a lot faster installations!
If you'd like more details about the unique node_modules structure that pnpm creates and
why it works fine with the Node.js ecosystem, read this small article: Flat node_modules is not the only way.
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Getting Started
Benchmark
pnpm is up to 2x faster than npm and Yarn classic. See all benchmarks here.
Benchmarks on an app with lots of dependencies:
