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: 2.404 sec
                  0.520 Mtransactions/sec
                  2.080 Mkeys/sec
Detect only:      2.266 sec
                  0.552 Mtransactions/sec
                  2.207 Mkeys/sec
Skiplist only:    1.594 sec
                  0.784 Mtransactions/sec
                  3.137 Mkeys/sec
Performance counters:
               Build: 0.071
                 Add: 0.0641
              Detect: 2.27
              D.Sort: 0.44
           D.Combine: 0.018
         D.CheckRead: 0.855
   D.CheckIntraBatch: 0.00903
        D.MergeWrite: 0.739
      D.RemoveBefore: 0.201

Radix tree (this implementation)

New conflict set: 1.743 sec
                  0.717 Mtransactions/sec
                  2.869 Mkeys/sec
Detect only:      1.611 sec
                  0.776 Mtransactions/sec
                  3.103 Mkeys/sec
Skiplist only:    0.919 sec
                  1.360 Mtransactions/sec
                  5.440 Mkeys/sec
Performance counters:
               Build: 0.0657
                 Add: 0.0628
              Detect: 1.61
              D.Sort: 0.442
           D.Combine: 0.0178
         D.CheckRead: 0.395
   D.CheckIntraBatch: 0.00776
        D.MergeWrite: 0.524
      D.RemoveBefore: 0.221

Our benchmark

Skip list

ns/op	op/s	err%	total	benchmark
270.07	3,702,706.03	0.4%	0.01	point reads
285.76	3,499,437.03	1.5%	0.01	prefix reads
532.54	1,877,794.90	0.7%	0.01	range reads
528.50	1,892,132.94	0.7%	0.01	point writes
516.53	1,935,978.22	0.9%	0.01	prefix writes
303.34	3,296,630.84	3.6%	0.05	range writes
502.88	1,988,553.24	2.0%	0.01	monotonic increasing point writes

Radix tree (this implementation)

ns/op	op/s	err%	total	benchmark
14.52	68,850,842.99	1.2%	0.01	point reads
60.89	16,422,538.22	1.5%	0.01	prefix reads
226.89	4,407,362.98	0.5%	0.01	range reads
22.99	43,498,198.49	0.2%	0.01	point writes
50.51	19,799,864.54	1.0%	0.01	prefix writes
82.50	12,121,212.12	2.6%	0.03	range writes
119.94	8,337,354.54	2.1%	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: 12.7863 seconds, 292.384 MB/s, Add: 19.8276 seconds, 35.4071 MB/s, Gc ratio: 23.5314%

radix tree

Check: 3.60187 seconds, 1037.94 MB/s, Add: 3.03958 seconds, 230.966 MB/s, Gc ratio: 52.3876%

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: 2.15925 seconds, 1731.4 MB/s, Add: 1.08519 seconds, 646.926 MB/s, Gc ratio: 52.1526%