Summary

In the fresh-resolve install path (no --frozen-lockfile, no usable lockfile), pacquet's dep-tree walker fetches package metadata serially as it recurses. pnpm pipelines/batches the same fetches, so by the time the walker reaches a node its packument is already in memory. The vlt.sh clean / cache / node_modules / lockfile variations exercise this path and pacquet is 4-12× slower than pnpm on deep-tree fixtures.

Benchmark evidence

From benchmarks.vlt.sh/latest/chart-data.json — selected rows where the lockfile is wiped or stale (pacquet 0.2.8 vs pnpm 11.2.2):

astro is a single astro@^5 dep that pulls hundreds of transitive packages — the worst case for a serial walker.

Current pacquet behavior

pacquet/crates/resolving-deps-resolver/src/resolve_dependency_tree.rs walks the dep tree with #[async_recursion]. Each resolve() for a (name, range) consults the per-(registry, name) packument cache initialized at install_with_fresh_lockfile.rs#L298-L334, but if there's no cached packument the fetch happens inline and blocks the recursion at that node.

There is no prefetcher / lookahead — descendants don't get their packuments requested until their parent's resolve() returns. With a tree depth of 10+ and fan-out of 5+, this serializes hundreds of HTTP requests that pnpm makes concurrent.

Proposed approach

Two complementary changes, both modeled on pnpm's resolver:

1. Prefetch the direct deps' packuments before starting the tree walk. Spawn n tokio tasks for the manifest's direct deps so the first recursion level has its packuments ready in cache.

2. Lookahead/batched fetch inside the recursion. When resolve() returns a manifest that lists dependencies / optionalDependencies, immediately fire packument fetches for each child name in parallel (de-duplicated via the existing per-(registry, name) mutex map). The recursion then awaits a cache hit instead of a blocking fetch.

pnpm's equivalent is in resolving/npm-resolver/src/index.ts and the prefetcher around installing/deps-resolver/src/resolveDependencyTree.ts.

This is implicitly part of #11633 Stage 2 Tier 1 ("Resolution graph & recursion engine") but worth tracking as a focused perf sub-task with the vlt.sh benchmark numbers attached so progress is measurable.

Expected impact

Closes the astro outlier across all lockfile-wiped variations. Smaller but meaningful gain on large and any other deep-tree resolve.

Related

• Rust Roadmap #11633 Stage 2 Tier 1 — full resolver port (umbrella)
• perf(pacquet): close the remaining install-phase sys-time gap to pnpm #11857 syscall-contention — orthogonal; this issue is about network metadata fetch, not file I/O
• pacquet: registry metadata fetch issues a single request — port pnpm's retry policy #11841 packument retry policy — orthogonal but in the same fetcher

Written by an agent (Claude Code, claude-opus-4-7).