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

Intended to replace FoundationDB's skip list.

FoundationDB's benchmark

Skip list

New conflict set: 4.189 sec
                  0.298 Mtransactions/sec
                  1.194 Mkeys/sec
Detect only:      3.990 sec
                  0.313 Mtransactions/sec
                  1.253 Mkeys/sec
Skiplist only:    2.849 sec
                  0.439 Mtransactions/sec
                  1.755 Mkeys/sec
Performance counters:
               Build: 0.0913
                 Add: 0.0998
              Detect: 3.99
              D.Sort: 0.808
           D.Combine: 0.0309
         D.CheckRead: 1.67
   D.CheckIntraBatch: 0.0305
        D.MergeWrite: 1.18
      D.RemoveBefore: 0.265

Radix tree (this implementation)

New conflict set: 2.965 sec
                  0.422 Mtransactions/sec
                  1.686 Mkeys/sec
Detect only:      2.761 sec
                  0.453 Mtransactions/sec
                  1.811 Mkeys/sec
Skiplist only:    1.580 sec
                  0.791 Mtransactions/sec
                  3.165 Mkeys/sec
Performance counters:
               Build: 0.0902
                 Add: 0.107
              Detect: 2.76
              D.Sort: 0.809
           D.Combine: 0.0309
         D.CheckRead: 0.658
   D.CheckIntraBatch: 0.0294
        D.MergeWrite: 0.921
      D.RemoveBefore: 0.305

Our benchmark

ns/op	op/s	err%	total	benchmark
325.60	3,071,225.77	4.8%	0.77	skip list (point reads)
297.15	3,365,278.10	1.7%	0.72	skip list (prefix reads)
408.79	2,446,222.23	1.0%	1.03	skip list (range reads)
261.88	3,818,471.08	1.3%	0.73	skip list (point writes)
253.54	3,944,191.08	0.1%	0.61	skip list (prefix writes)
258.73	3,865,078.52	0.8%	0.62	skip list (range writes)
489.56	2,042,648.19	1.8%	0.01	skip list (monotonic increasing point writes)
14.83	67,446,579.75	0.1%	0.04	radix tree (point reads)
59.68	16,756,917.37	0.1%	0.14	radix tree (prefix reads)
287.32	3,480,485.22	1.2%	0.69	radix tree (range reads)
46.59	21,461,855.59	0.2%	0.12	radix tree (point writes)
83.70	11,946,755.99	0.1%	0.20	radix tree (prefix writes)
100.75	9,925,723.26	0.6%	0.25	radix tree (range writes)
118.37	8,448,345.29	0.6%	0.01	radix tree (monotonic increasing point writes)