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 20.0.0 (++20241120082228+86734c857724-1~exp1~20241120202359.554)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-20/bin

Microbenchmark

Skip list

ns/op	op/s	err%	ins/op	cyc/op	IPC	bra/op	miss%	total	benchmark
161.29	6,200,056.17	0.1%	3,014.03	831.04	3.627	504.59	0.0%	1.93	point reads
158.32	6,316,160.64	0.1%	2,954.16	815.80	3.621	490.17	0.0%	1.89	prefix reads
237.39	4,212,409.50	0.2%	3,592.41	1,233.96	2.911	629.31	0.0%	2.84	range reads
442.11	2,261,878.94	0.0%	4,450.57	2,314.25	1.923	707.92	2.1%	5.28	point writes
439.89	2,273,308.53	0.1%	4,410.22	2,302.29	1.916	694.74	2.1%	5.25	prefix writes
290.96	3,436,936.78	0.0%	2,315.38	1,528.68	1.515	396.69	3.3%	3.49	range writes
476.93	2,096,762.02	0.6%	6,999.33	2,484.94	2.817	1,251.73	1.3%	0.06	monotonic increasing point writes
131,736.57	7,590.91	1.1%	807,444.50	704,941.71	1.145	144,584.60	0.9%	0.01	worst case for radix tree
45.50	21,978,369.95	1.1%	902.00	232.36	3.882	132.00	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
12.36	80,885,626.43	0.2%	243.56	63.62	3.828	31.07	0.6%	0.15	point reads
14.18	70,502,196.81	0.1%	297.72	73.13	4.071	40.31	0.5%	0.17	prefix reads
33.44	29,901,623.04	0.1%	767.90	172.42	4.454	101.32	0.2%	0.40	range reads
19.48	51,342,564.70	0.3%	374.45	100.43	3.728	48.92	0.5%	0.23	point writes
37.46	26,694,471.44	0.1%	672.00	193.14	3.479	101.28	0.3%	0.45	prefix writes
38.78	25,784,784.34	0.0%	738.26	199.93	3.693	111.59	0.1%	0.47	range writes
76.05	13,148,995.74	0.7%	1,450.77	397.16	3.653	275.72	0.0%	0.01	monotonic increasing point writes
286,920.33	3,485.29	0.4%	4,117,948.00	1,521,352.00	2.707	714,833.00	0.1%	0.01	worst case for radix tree
95.66	10,453,798.72	0.5%	1,986.00	495.04	4.012	315.00	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: 4.53508 seconds, 371.81 MB/s, Add: 3.81222 seconds, 150.919 MB/s, Gc ratio: 33.66%, Peak idle memory: 5.61007e+06

radix tree

Check: 0.957735 seconds, 1760.6 MB/s, Add: 1.19942 seconds, 479.678 MB/s, Gc ratio: 38.6069%, Peak idle memory: 2.05667e+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: 0.804598 seconds, 2095.69 MB/s, Add: 0.671221 seconds, 857.147 MB/s, Gc ratio: 35.0034%, Peak idle memory: 0