Patches

This directory holds pnpm patches applied on install via pnpm.patchedDependencies in the root package.json. Each .patch is a diff against the published package. Most are small and self-explanatory from the diff; the non-obvious ones are documented below.

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@remix-run/[email protected] — route-matching memoization

File: patches/@[email protected] (patches dist/router.cjs.js)

What it does

Four changes to matchRoutesImpl / compilePath, all derived from work that depends only on the static route manifest:

1. Cache flattened + ranked branches per route-tree (WeakMap keyed by the routes ref). flattenRoutes() + rankRouteBranches() were recomputed on every matchRoutes call across all ~436 webapp routes.

2. Hoist decodePath(pathname) out of the branch-match loop — it's loop-invariant but was recomputed once per branch.

3. Memoize compilePath compiled regexes by path|caseSensitive|end (bounded Map, cap 2000). The matcher RegExp was rebuilt on every matchPath call.

4. Bucket ranked branches by first static path segment (WeakMap keyed by the branch array). Even with (1)–(3), matching was still a linear scan calling matchPath on every branch until one matched — O(route table) per request, now across 521 route files. Branches are indexed by their lowercased leading segment, with one always-considered list for branches whose leading segment is dynamic, splat or optional (and for root/pathless paths). A request walks only its own bucket merged with that list.

   Ordering is preserved exactly: both lists hold indexes into the already rank-sorted branch array and are walked in ascending-index order, so the first match found is the same branch the full scan would have found. Bucketing lowercases on both sides, so case-insensitive matching still resolves and caseSensitive: true routes are still rejected by matchPath itself. A pathname whose own leading segment can't be bucketed falls back to the full scan.

   Verified equivalent to the unpatched matcher over 20,050 pathnames (literal, dynamic, splat, optional, case variants, basenames, percent-encoded). The semantics it depends on are pinned by apps/webapp/test/routeMatchingPatch.test.ts, which asserts matching behaviour rather than the optimisation, so it still passes without the patch.

Why

Profiling the realtime runs feed under load (100 concurrent tag feeds, ~425 req/s) found ~68% of webapp CPU was spent in react-router's matchRoutes — re-flattening, re-ranking, and re-compiling the entire route table on every request. It is not a dev artifact: there is no NODE_ENV gate, and a NODE_ENV=production profile was identical (67.9% vs 68.3%). The realtime feed's high request rate (each long-poll returns fast and immediately re-polls) just amplifies a latent per-request cost that large route tables pay everywhere.

Measured on a single instance, same load, before vs after this patch:

	before	after
active CPU (self-time / window)	28.3s	18.5s (−34%)
route-matching self-time	19.2s	7.5s (−61%)
event-loop lag p99	322ms	113ms (−65%)
idle headroom	26%	52%

The realtime machinery itself (router/hydrate/serialize/diff) was ~0% — the bottleneck was entirely generic Remix request overhead.

Change (4) was added later, from a CPU audit of the engine-facing worker-action routes (apps/webapp/test/bench). With (1)–(3) already in place, route matching was still 10.4% of on-CPU time on that path — the residual linear scan rather than any recompilation. Bucketing took route-matching self-time from 3.6s to 1.3s (−64%) over a 90s window at ~300 req/s.

Upstream status (why we patch instead of upgrade)

This is a known, acknowledged inefficiency, and it is only partially fixed in React Router v7 — which we can't adopt without a full Remix 2 → RR7 framework migration.

• Issue #8653 "Performance issues" reported it (a user with 12k routes, ~67ms per match) and was closed as a dup of the route-ranking discussion remix#4786.
• PR #14866 "Optimize route matching performance with caching" implemented exactly this patch (hoist decodePath, cache compilePath, cache flatten/rank), claiming ~80% route-matching CPU reduction on a 400+ route app. It was closed, not merged.
• PR #14967 "perf: cache flattened/ranked route branches" is the partial fix that did ship (in v7): it caches only the branches, threaded via a precomputedBranches param through the framework's server-runtime (~15% SSR gain). It does not cache compilePath — that regex rebuild remains even on main. (PR #14971 added client-side wins.)

The maintainer's reasoning for closing the fuller PR (#14866), verbatim:

"This is great as a patch-package optimization for those who want it, but we are actively working on integrating the more performant route-pattern library from Remix 3 so we'd rather just do the right 'fix' and ship the new algorithm instead of trying to band-aide perf improvements to the existing algorithm which was written with a very different set of constraints. Those constraints come from early v6 when it was only declarative mode so route trees were defined at render time and thus had to be re-flattened/re-ranked/re-compiled every time."

So: the re-compute-everything design is a holdover from early React Router v6 declarative mode (route trees defined at render time, so recomputing was correct then). The maintainer explicitly endorsed patch-package as the interim approach and is betting on the Remix 3 route-pattern rewrite for the real fix. This patch is that sanctioned stopgap — and it also includes the compilePath cache the merged PR left on the table.

Safety

Pure memoization of deterministic, internal-only values:

• flattenRoutes/rankRouteBranches and the compiled regexes depend solely on the static route manifest; the cached values are never returned to or mutated by the framework.
• The compiled RegExp has no /g flag, so .exec() carries no cross-call state — safe to share under concurrency.
• The branch cache is a WeakMap (collected with its route tree); the compile cache is bounded at 2000 entries (route patterns are a static set; the cap only guards any dynamic matchPath() use).
• Targets the CJS build (dist/router.cjs.js), which the webapp server loads at runtime (@remix-run/router is not bundled into the server build).

When to remove

Drop this patch if/when the webapp moves to React Router v7+ (which threads precomputedBranches itself) or the Remix 3 route-pattern matcher lands. Re-profile at that point — the compilePath cache may still be worth keeping since upstream never added it.