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The C++ simdjson baseline

What the original does on this machine, same corpus bytes, single thread, minimum of eight. simdjson 4.6.4 amalgamation, clang -O3 -march=native; make bench-cpp reproduces it (the amalgamation is fetched on demand, not committed). Our numbers are the same session's BenchmarkCorpus minima.

MB/s, single thread C++ parse (validated tape) ours Parse (validated) ours Scan (index only)
twitter 6,997 3,189 12,537
citm 6,856 3,150 8,902
canada 1,602 1,982 6,808

Reading it honestly:

  • C++ leads validated parsing 2.2× on the string-heavy corpora. Its tape build fuses structure, UTF-8 and value validation into one branch-free pass; our Parse is the index plus a grammar descent. That is the architectural bill for a navigable Doc with encoding/json's exact error surface, in Go, with no cgo.
  • canada is ours, against the original. 1,980 vs 1,602: the SWAR digit runs in the number validator outrun their float parse on the corpus that is nothing but floats.
  • Scan is a different contract (no validation) and is not comparable to their parse; the row is there because its consumers exist.
  • Their ondemand two-field read measures 14,048 MB/s on twitter — the never-materialize design at its best; our GetPath class serves the same use.
  • Past 8 MB the comparison inverts. C++ simdjson does not parallelize a single document (one worker thread pipelines stage 1 of the next batch; ceiling 2× and only for many-document streams). This library shards one document: Parse 11.5 GB/s and Scan 31 GB/s at 64 MB on this machine, against their single-thread numbers above.

The gap statement for the README stays what it is: fastest Go JSON library; the original C++ remains faster at single-threaded validated parsing of string-heavy documents, and this table is the size of that gap.