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
263.10	3,800,889.33	1.6%	0.64	skip list (point reads)
256.36	3,900,800.96	1.7%	0.61	skip list (prefix reads)
526.95	1,897,714.85	1.6%	1.23	skip list (range reads)
546.54	1,829,676.97	0.5%	1.31	skip list (point writes)
539.23	1,854,511.73	0.5%	1.29	skip list (prefix writes)
266.68	3,749,799.99	0.6%	0.65	skip list (range writes)
18.31	54,612,706.60	0.4%	0.04	radix tree (point reads)
48.78	20,498,870.77	0.2%	0.12	radix tree (prefix reads)
347.16	2,880,474.86	0.9%	0.83	radix tree (range reads)
34.80	28,734,706.67	3.6%	0.09	radix tree (point writes)
70.34	14,216,970.16	1.4%	0.17	radix tree (prefix writes)
82.41	12,134,555.86	1.0%	0.20	radix tree (range writes)