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

Intended as an alternative to FoundationDB's skip list.

Hardware for all benchmarks is an AMD Ryzen 9 7900 with (2x32GB) 5600MT/s CL28-34-34-89 1.35V RAM.

$ clang++ --version

Ubuntu clang version 21.1.8 (6ubuntu1)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-21/bin

Microbenchmark

Skip list

ns/op	op/s	err%	ins/op	cyc/op	IPC	bra/op	miss%	total	benchmark
164.29	6,086,873.38	0.0%	3,107.03	604.19	5.142	558.59	0.0%	1.96	point reads
161.05	6,209,395.38	0.1%	3,036.76	592.21	5.128	539.35	0.0%	1.93	prefix reads
239.55	4,174,539.38	0.1%	3,722.71	880.68	4.227	692.00	0.0%	2.86	range reads
354.75	2,818,919.14	0.7%	4,523.64	1,304.75	3.467	720.22	2.0%	4.23	point writes
345.32	2,895,878.47	0.1%	4,484.57	1,270.31	3.530	705.00	1.8%	4.12	prefix writes
193.48	5,168,547.42	0.1%	2,224.10	711.72	3.125	377.17	3.3%	2.32	range writes
404.89	2,469,777.50	2.4%	6,855.96	1,489.70	4.602	1,227.82	1.3%	0.05	monotonic increasing point writes
134,231.80	7,449.80	1.9%	812,045.25	495,770.40	1.638	151,246.50	0.9%	0.01	worst case for radix tree
37.80	26,454,311.17	0.4%	701.00	139.14	5.038	102.00	0.0%	0.01	create and destroy

Radix tree (this implementation)

ns/op	op/s	err%	ins/op	cyc/op	IPC	bra/op	miss%	total	benchmark
12.89	77,565,115.56	0.1%	244.55	47.43	5.155	34.21	0.6%	0.15	point reads
15.11	66,162,047.76	0.1%	297.79	55.60	5.356	43.23	0.4%	0.18	prefix reads
36.29	27,559,358.29	0.1%	783.16	133.44	5.869	109.52	0.2%	0.43	range reads
20.53	48,719,405.55	0.1%	381.81	75.51	5.057	51.04	0.5%	0.25	point writes
39.37	25,402,042.40	0.1%	685.00	144.83	4.730	106.72	0.3%	0.47	prefix writes
43.78	22,843,841.63	0.1%	800.40	161.06	4.970	127.36	0.1%	0.53	range writes
78.37	12,760,008.75	1.0%	1,452.61	288.24	5.040	278.69	0.1%	0.01	monotonic increasing point writes
322,885.50	3,097.07	1.5%	4,362,382.00	1,183,852.00	3.685	765,301.00	0.1%	0.01	worst case for radix tree
99.99	10,000,718.79	0.4%	1,775.00	367.93	4.824	288.00	0.0%	0.01	create and destroy

"Real data" test

Point queries only. 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: 4.62967 seconds, 352.195 MB/s, Add: 3.34177 seconds, 167.771 MB/s, Gc ratio: 37.9399%, Peak idle memory: 5.51852e+06

radix tree

Check: 1.00477 seconds, 1622.8 MB/s, Add: 1.21142 seconds, 462.808 MB/s, Gc ratio: 39.4716%, Peak idle memory: 2.0226e+06

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: 0.854254 seconds, 1908.74 MB/s, Add: 0.632626 seconds, 886.232 MB/s, Gc ratio: 41.0827%, Peak idle memory: 0