perf(router): cache-friendly static child lookup#3024
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findStaticChild scanned []*node and dereferenced every child to read its one-byte label — a pointer chase per static step. Maintain a parallel scLabels []byte (kept in sync in addStaticChild, newNode, the insert split, and Remove) and scan that contiguous slice instead, indexing into staticChildren only on a hit. benchstat (n=6): RouterStaticRoutes-14 8.49µ -> 8.01µ -5.67% (p=0.002) RouterGitHubAPI-14 16.93µ -> 16.45µ -2.86% (p=0.002) RouterParseAPI / GooglePlusAPI: neutral (param-heavy) allocations: 0, unchanged Also fold the is-leaf recomputation (duplicated across 5 sites, with the Remove copy subtly using len()==0 vs == nil) into a single refreshLeaf() helper that uses len() so it is correct whether staticChildren is nil or an emptied-but-non-nil slice left after a removal. Split out of #3023 so the router and JSON changes can be reviewed independently (requested by @aldas). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Split out of #3023 at @aldas's request so the router and JSON changes land as independent PRs.
What
findStaticChildscanned[]*nodeand dereferenced every child just to read its one-byte label — a pointer chase per static step on the routing hot path. This adds a parallelscLabels []byte(kept in sync inaddStaticChild,newNode, the insert split, andRemove) and scans that contiguous slice instead, indexing intostaticChildrenonly on a hit.It also folds the is-leaf recomputation — previously duplicated across 5 sites, with the
Removecopy subtly usinglen()==0while the others used== nil— into a singlerefreshLeaf()helper that useslen(), so it is correct whetherstaticChildrenisnilor an emptied-but-non-nil slice left after a removal.Numbers
The companion ServeHTTP benchmark harness lands with #3023 (the JSON PR); routing benchmarks there exercise this change once both merge.
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