Niels Lohmann 5b08041308 Look up the keys of big ordered_json objects in a hash table ...

ordered_map keeps its elements in a vector and searches it linearly for
every key it adds, so parsing an object with n keys into ordered_json took
O(n^2) key comparisons: 33 billion instructions for one object with 30 000
keys, where json needs 245 million. From 64 keys on, the DOM parser now
keeps a hash table of the keys of the open object (hashes and positions
only; the elements stay in the vector) and finds duplicate keys there. The
result is the same, including the position of a key that occurs twice.
Smaller objects, std::map based objects and key types without std::hash
are untouched.

ordered_json parse, macOS instructions: object with 1 000 keys 64.8 M ->
14.6 M, 10 000 keys 5 104 M -> 38.7 M, 30 000 keys 33 358 M -> 89 M.
Linux Ir of an object with 2 000 keys: 43.0 M -> 1.9 M (GCC), 37.9 M ->
1.8 M (Clang).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

2026-10-22 09:27:58 +02:00

..

json_fwd.hpp

Scan strings with SSE2, SSSE3, or NEON (#5853)

2026-10-21 20:00:50 +02:00

json_literals.hpp

Move the user-defined string literals to <nlohmann/json_literals.hpp> and add JSON_NO_AUTOMATIC_UDLS (#5610)

2026-09-30 20:08:17 +02:00

json_view.hpp

Use standard library helpers where available, with C++11 fallbacks (#5876)

2026-10-21 20:14:59 +02:00

json.hpp

Look up the keys of big ordered_json objects in a hash table

2026-10-22 09:27:58 +02:00