perf: fast-path strict json imports#840
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Motivation: Kube-prometheus imports large strict JSON files; parsing them through the full Jsonnet parser creates avoidable AST and materialization work. Modification: Add a strict .json import fast path shared by CachedResolver and Preloader, trim visitor work, build race-free inline-array objects for imported JSON, and reuse the no-offset position for imported literals. Result: Strict JSON imports keep Jsonnet fallback semantics for non-strict inputs while reducing parse and manifestation overhead for large imported JSON data.
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Motivation:
Real-world workloads such as kube-prometheus import large strict JSON files. Parsing those files through the full Jsonnet parser creates avoidable parser, AST, and manifestation work.
Key Design Decision:
The fast path only accepts strict
.jsoninput and falls back to normal Jsonnet parsing for malformed JSON, duplicate keys, non-finite numbers, parser-depth overflow, and defensive numeric parse failures. Imported JSON objects use a race-free inline-arrayVal.Objlayout: field caching is disabled for parse-cache-shared literals, and single-field objects avoid lazyvalue0mutation. JSON value positions reusefileScope.noOffsetPosbecause strict JSON imports do not execute code and per-element positions are not consumed for stack traces.Modification:
Add a shared strict JSON import visitor in
CachedResolver, wire it intoPreloader, trim duplicate-key/string visitor work, use inline object layout for imported JSON objects, and add shared-cache/concurrency regression tests.Benchmark Results:
entry-kube-prometheus.jsonnet -J vendor)223.351 +/- 12.742 ms139.041 +/- 2.847 ms-37.75%~235 msstarting stack135.9 +/- 1.2 ms~ -42%cumulative88.087 +/- 1.737 ms, remaining gap1.54x.manifestJsonEx 0.053,realistic2 39.485,large_string_template 1.102,gen_big_object 0.801Analysis:
The PR keeps Jsonnet compatibility by treating the JSON parser as an optional strict fast path, not a replacement parser. The added JVM-only concurrency tests exercise shared parse-cache reuse; cross-platform JSON import tests cover the platform-neutral behavior.
References:
Source exploration commits: He-Pin/sjsonnet
995b0822,114bd69f,52e22696,ca6f24d5.Result:
Local
./mill --no-server -j 1 __.reformatand./mill --no-server -j 1 __.testpassed on this split branch (2066/2066).