A data structure for optimistic concurrency control on ranges of bitwise-lexicographically-ordered keys.

Intended to replace FoundationDB's skip list.

Hardware for all benchmarks is a mac m1 2020.

FoundationDB's benchmark

Skip list

New conflict set: 1.964 sec
                  0.637 Mtransactions/sec
                  2.546 Mkeys/sec
Detect only:      1.859 sec
                  0.672 Mtransactions/sec
                  2.690 Mkeys/sec
Skiplist only:    1.275 sec
                  0.980 Mtransactions/sec
                  3.921 Mkeys/sec
Performance counters:
               Build: 0.0496
                 Add: 0.0539
              Detect: 1.86
              D.Sort: 0.412
           D.Combine: 0.0139
         D.CheckRead: 0.682
   D.CheckIntraBatch: 0.00673
        D.MergeWrite: 0.593
      D.RemoveBefore: 0.148

Radix tree (this implementation)

New conflict set: 1.289 sec
                  0.970 Mtransactions/sec
                  3.879 Mkeys/sec
Detect only:      1.199 sec
                  1.043 Mtransactions/sec
                  4.170 Mkeys/sec
Skiplist only:    0.542 sec
                  2.305 Mtransactions/sec
                  9.220 Mkeys/sec
Performance counters:
               Build: 0.0395
                 Add: 0.0492
              Detect: 1.2
              D.Sort: 0.411
           D.Combine: 0.0135
         D.CheckRead: 0.22
   D.CheckIntraBatch: 0.00652
        D.MergeWrite: 0.322
      D.RemoveBefore: 0.223

Our benchmark

Skip list

ns/op	op/s	err%	total	benchmark
249.47	4,008,533.72	0.5%	0.01	point reads
236.78	4,223,252.12	0.4%	0.01	prefix reads
432.76	2,310,737.74	0.1%	0.01	range reads
449.42	2,225,105.96	0.5%	0.01	point writes
438.47	2,280,674.39	0.3%	0.01	prefix writes
242.92	4,116,581.59	3.7%	0.02	range writes
553.31	1,807,319.60	0.7%	0.01	monotonic increasing point writes

Radix tree (this implementation)

ns/op	op/s	err%	total	benchmark
19.35	51,669,510.11	0.2%	0.01	point reads
56.64	17,655,057.00	0.2%	0.01	prefix reads
217.04	4,607,450.05	0.2%	0.01	range reads
26.31	38,012,015.29	0.0%	0.01	point writes
41.45	24,124,003.19	0.2%	0.01	prefix writes
48.33	20,691,082.14	0.0%	0.01	range writes
84.92	11,775,856.81	4.0%	0.01	monotonic increasing point writes

"Real data" test

Point queries only, best of three runs. Gc ratio is the ratio of time spent doing garbage collection to time spent adding writes or doing garbage collection. Lower is better.

skip list

Check: 11.267 seconds, 331.812 MB/s, Add: 5.33323 seconds, 131.635 MB/s, Gc ratio: 45.4671%

radix tree

Check: 2.48508 seconds, 1504.38 MB/s, Add: 2.07295 seconds, 338.666 MB/s, Gc ratio: 42.2825%

hash table

(The hash table implementation doesn't work on range queries, and its purpose is to provide an idea of how fast point queries can be)

Check: 1.83931 seconds, 2032.56 MB/s, Add: 0.607861 seconds, 1154.93 MB/s, Gc ratio: 48.7142%