Niels Lohmann 74a96a0bbb Binary writers: zero only a window ahead of the vector sink's position ...

output_vector_sink grew the vector by resizing it to its whole new
capacity. resize() zeroes the characters it adds, so every doubling
zeroed megabytes of a fresh allocation at once: that faults in all its
pages and evicts them from the cache before the writer reaches them,
and the writer's stores then miss again. The sink now reserves the same
capacity as before but resizes the vector only to 64 KiB
(vector_sink_window) ahead of the position, which is still cached when
the writer's stores come.

to_cbor(), to_msgpack(), to_ubjson(), to_bjdata() and to_bon8() of an
array of one million numbers into a fresh vector: 4-26 % faster on x86
(Skylake laptop with Apple clang 13, Haswell VPS with GCC 16 and
Clang 23), 1-2.5 % on Apple M1 Max; other documents unchanged (within
0.4 % in reruns). The capacity and growth of the vector are as before.

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

2026-11-03 16:12:16 +01:00

..

nlohmann

Binary writers: zero only a window ahead of the vector sink's position

2026-11-03 16:12:16 +01:00