sparse vectors support

[agourlay]

This PR adds support for sparse vectors.

cargo run -- -n 10000 --dim 2048 --search --sparse-vectors --on-disk-index

--- Search timings ---
Min search time: 0.000557541
Avg search time: 0.10446536149315065
p95 search time: 0.380973509
p99 search time: 0.412968431
Max search time: 0.475767685
--- Server timings ---
Min search time: 0.000256465
Avg search time: 0.10361921244292235
p95 search time: 0.379839804
p99 search time: 0.411853914
Max search time: 0.474702047
--- RPS ---
Min rps: 21.732467847307905
Avg rps: 37.99061218217272
p95 rps: 67.7935806787728
p99 rps: 100.30751254181632
Max rps: 119.50527106181168

result from my busy laptop

Future work

• load sparse vectors from file (maybe SLADE format as well)

[timvisee]

I've changed the --on-disk-index flag from bool to Option<bool>. It makes it a bit less nice to invoke because it requires --on-disk-index true this way, but it's important to support all three variants: None, Some(true), Some(false).

[timvisee]

Also, here are results on my busy machine:

$ bfb -n 10000 --dim 2048 --search --sparse-vectors --on-disk-index true
--- Search timings ---
Min search time: 0.000249218
Avg search time: 0.022734802924000017
p95 search time: 0.044381216
p99 search time: 0.046892587
Max search time: 0.073775338
--- Server timings ---
Min search time: 0.00008789
Avg search time: 0.022489696575899967
p95 search time: 0.044086216
p99 search time: 0.046608329
Max search time: 0.073426011
--- RPS ---
Min rps: 86.02060530603548
Avg rps: 88.08529494580816
p95 rps: 89.89534703227301
p99 rps: 90.0289776225274
Max rps: 1116.6270267271339

$ bfb -n 10000 --dim 2048 --search --sparse-vectors --on-disk-index false
--- Search timings ---
Min search time: 0.000220528
Avg search time: 0.02254625945380004
p95 search time: 0.044441273
p99 search time: 0.047454161
Max search time: 0.068276639
--- Server timings ---
Min search time: 0.000060349
Avg search time: 0.022295191263000034
p95 search time: 0.044145646
p99 search time: 0.047097525
Max search time: 0.067878882
--- RPS ---
Min rps: 86.89633905494993
Avg rps: 89.26247468255279
p95 rps: 93.62051455556441
p99 rps: 103.21010632830085
Max rps: 237.56436290017766

[KShivendu]

Small change: #21