ruby-grape / grape / 35225407633

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Pull #2943

github

Speed up matching among many parameterized routes

A request the static table cannot answer is matched against its method's
whole union: every route's pattern, each expanding every literal character
into an alternation with its percent-encodings. On an API with 200
parameterized routes that match is most of the request -- 43-53 µs of
~68 µs without a JIT -- and it grows with every route registered ahead of
the one that matches.

A route that spells out a literal at some path segment, with only literals
and plain params ahead of it, can only match paths carrying that literal
there. Router#compile! now picks, per method, the segment position that
splits the routes best and builds one union per literal there. Each holds
the routes that literal names plus every route the segment cannot tell
apart, in registration order, so matching a request against the union for
its own segment picks the route the full union would have picked.

Paths holding a '%' (a literal may match its percent-encoding) or a newline
(the patterns end in \Z) still go through the full union, as do methods
with fewer than eight routes or with no segment that halves them.

A route sits at a different capture group in each bucket than it does in
the router's union, so a bucket carries its routes' captures renumbered for
its own union -- every capture is a fixed offset from the route's own
group, so one number shifts the whole map -- and hands them over with the
match. Reading the captures out of the match already in hand, rather than
having Mustermann match the path a second time, costs 0.28 µs and 5 objects
where the second match cost 1.48 µs and 10: on the 200-route API, +15.5%
without a JIT and +24.2% with YJIT, at 29 -> 22 allocations per request. A
route whose captures a union match cannot reproduce is matched by
Mustermann as before.

The buckets ride in the per-method entry #transaction already reads, so a
method without them pays no extra lookup. A bucket whose alternatives
another... (continued)

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