mokurin000 / sort-nums-bench

sort-nums-bench

let mut v = iter.collect::<Vec<_>>()
v.sort_unstable();

v.s.

let s = iter.collect::<BTreeSet<_>>();

The former is significantly faster (unless input are mostly Eq), because:

1. Rust's sort_unstable sorts items in-place, avoids bunch of heap allocations, at the cost of stablity.
2. Constructing a BTreeSet however invokes lots of heap allocations

So while the worst time complexity of BTreeMap inserts is O(n log n), the best time complexity of in-place merge sort is O(n log n) (O(n²) for the worst case), in practice the number of heap allocations, or the constant in other words, results collect::<Vec<_>> + sort_unstable to be much faster than collect::<BTreeSet<_>>.

results

Environment:

Kernel: 6.7.6-zen1-1-zen
CPU: 12th Gen Intel i7-12700H (20) @ 4.600GHz
Memory: DDR5 8GB Dual-Channel (M425R1GB4BB0-CQKOL)

RAND_NUMS=1024

mimalloc:

test tests::bench_btree_collect     ... bench:      31,213 ns/iter (+/- 293)
test tests::bench_vec_sort          ... bench:      26,919 ns/iter (+/- 129)
test tests::bench_vec_sort_unstable ... bench:       9,276 ns/iter (+/- 446)

tcmalloc:

test tests::bench_btree_collect     ... bench:      31,366 ns/iter (+/- 394)
test tests::bench_vec_sort          ... bench:      27,438 ns/iter (+/- 74)
test tests::bench_vec_sort_unstable ... bench:      10,006 ns/iter (+/- 110)

jemalloc:

test tests::bench_btree_collect     ... bench:      32,808 ns/iter (+/- 225)
test tests::bench_vec_sort          ... bench:      28,886 ns/iter (+/- 163)
test tests::bench_vec_sort_unstable ... bench:       9,695 ns/iter (+/- 220)

snmalloc:

test tests::bench_btree_collect     ... bench:      32,190 ns/iter (+/- 219)
test tests::bench_vec_sort          ... bench:      28,850 ns/iter (+/- 178)
test tests::bench_vec_sort_unstable ... bench:       8,971 ns/iter (+/- 155)

ferroc:

test tests::bench_btree_collect     ... bench:      33,395 ns/iter (+/- 145)
test tests::bench_vec_sort          ... bench:      29,255 ns/iter (+/- 146)
test tests::bench_vec_sort_unstable ... bench:       9,765 ns/iter (+/- 166)

rpmalloc:

test tests::bench_btree_collect     ... bench:      31,330 ns/iter (+/- 145)
test tests::bench_vec_sort          ... bench:      27,132 ns/iter (+/- 101)
test tests::bench_vec_sort_unstable ... bench:       9,201 ns/iter (+/- 326)

PtMalloc:

test tests::bench_btree_collect     ... bench:      33,449 ns/iter (+/- 275)
test tests::bench_vec_sort          ... bench:      27,019 ns/iter (+/- 121)
test tests::bench_vec_sort_unstable ... bench:       8,602 ns/iter (+/- 518)