## Introduction
skipmap is a high-performance concurrent map based on skip list. In typical pattern(one million operations, 90%LOAD 9%STORE 1%DELETE), the skipmap up to 3x ~ 10x faster than the built-in sync.Map.
The main idea behind the skipmap is [A Simple Optimistic Skiplist Algorithm]().
Different from the sync.Map, the items in the skipmap are always sorted, and the `Load` and `Range` operations are wait-free (A goroutine is guaranteed to complete a operation as long as it keeps taking steps, regardless of the activity of other goroutines).
## Features
- Concurrent safe API with high-performance.
- Wait-free Load and Range operations.
- Sorted items.
## When should you use skipmap
In these situations, `skipmap` is better
- **Sorted elements is needed**.
- **Concurrent calls multiple operations**. such as use both `Load` and `Store` at the same time.
In these situations, `sync.Map` is better
- Only one goroutine access the map for most of the time, such as insert a batch of elements and then use only `Load` (use built-in map is even better).
## QuickStart
```go
package main
import (
"fmt"
"github.com/bytedance/gopkg/collection/skipmap"
)
func main() {
l := skipmap.NewInt()
for _, v := range []int{10, 12, 15} {
l.Store(v, v+100)
}
v, ok := l.Load(10)
if ok {
fmt.Println("skipmap load 10 with value ", v)
}
l.Range(func(key int, value interface{}) bool {
fmt.Println("skipmap range found ", key, value)
return true
})
l.Delete(15)
fmt.Printf("skipmap contains %d items\r\n", l.Len())
}
```
## Benchmark
Go version: go1.16.2 linux/amd64
CPU: AMD 3700x(8C16T), running at 3.6GHz
OS: ubuntu 18.04
MEMORY: 16G x 2 (3200MHz)
```shell
$ go test -run=NOTEST -bench=. -benchtime=100000x -benchmem -count=20 -timeout=60m > x.txt
$ benchstat x.txt
```
```
name time/op
Int64/Store/skipmap-16 158ns ±12%
Int64/Store/sync.Map-16 700ns ± 4%
Int64/Load50Hits/skipmap-16 10.1ns ±14%
Int64/Load50Hits/sync.Map-16 14.8ns ±23%
Int64/30Store70Load/skipmap-16 50.6ns ±20%
Int64/30Store70Load/sync.Map-16 592ns ± 7%
Int64/1Delete9Store90Load/skipmap-16 27.5ns ±13%
Int64/1Delete9Store90Load/sync.Map-16 480ns ± 4%
Int64/1Range9Delete90Store900Load/skipmap-16 34.2ns ±26%
Int64/1Range9Delete90Store900Load/sync.Map-16 1.00µs ±12%
String/Store/skipmap-16 171ns ±15%
String/Store/sync.Map-16 873ns ± 4%
String/Load50Hits/skipmap-16 21.3ns ±38%
String/Load50Hits/sync.Map-16 19.9ns ±12%
String/30Store70Load/skipmap-16 75.6ns ±16%
String/30Store70Load/sync.Map-16 726ns ± 5%
String/1Delete9Store90Load/skipmap-16 34.3ns ±20%
String/1Delete9Store90Load/sync.Map-16 584ns ± 5%
String/1Range9Delete90Store900Load/skipmap-16 41.0ns ±21%
String/1Range9Delete90Store900Load/sync.Map-16 1.17µs ± 8%
name alloc/op
Int64/Store/skipmap-16 112B ± 0%
Int64/Store/sync.Map-16 128B ± 0%
Int64/Load50Hits/skipmap-16 0.00B
Int64/Load50Hits/sync.Map-16 0.00B
Int64/30Store70Load/skipmap-16 33.0B ± 0%
Int64/30Store70Load/sync.Map-16 81.2B ±11%
Int64/1Delete9Store90Load/skipmap-16 10.0B ± 0%
Int64/1Delete9Store90Load/sync.Map-16 57.9B ± 5%
Int64/1Range9Delete90Store900Load/skipmap-16 10.0B ± 0%
Int64/1Range9Delete90Store900Load/sync.Map-16 261B ±17%
String/Store/skipmap-16 144B ± 0%
String/Store/sync.Map-16 152B ± 0%
String/Load50Hits/skipmap-16 15.0B ± 0%
String/Load50Hits/sync.Map-16 15.0B ± 0%
String/30Store70Load/skipmap-16 54.0B ± 0%
String/30Store70Load/sync.Map-16 96.9B ±12%
String/1Delete9Store90Load/skipmap-16 27.0B ± 0%
String/1Delete9Store90Load/sync.Map-16 74.2B ± 4%
String/1Range9Delete90Store900Load/skipmap-16 27.0B ± 0%
String/1Range9Delete90Store900Load/sync.Map-16 257B ±10%
name allocs/op
Int64/Store/skipmap-16 3.00 ± 0%
Int64/Store/sync.Map-16 4.00 ± 0%
Int64/Load50Hits/skipmap-16 0.00
Int64/Load50Hits/sync.Map-16 0.00
Int64/30Store70Load/skipmap-16 0.00
Int64/30Store70Load/sync.Map-16 1.00 ± 0%
Int64/1Delete9Store90Load/skipmap-16 0.00
Int64/1Delete9Store90Load/sync.Map-16 0.00
Int64/1Range9Delete90Store900Load/skipmap-16 0.00
Int64/1Range9Delete90Store900Load/sync.Map-16 0.00
String/Store/skipmap-16 4.00 ± 0%
String/Store/sync.Map-16 5.00 ± 0%
String/Load50Hits/skipmap-16 1.00 ± 0%
String/Load50Hits/sync.Map-16 1.00 ± 0%
String/30Store70Load/skipmap-16 1.00 ± 0%
String/30Store70Load/sync.Map-16 2.00 ± 0%
String/1Delete9Store90Load/skipmap-16 1.00 ± 0%
String/1Delete9Store90Load/sync.Map-16 1.00 ± 0%
String/1Range9Delete90Store900Load/skipmap-16 1.00 ± 0%
String/1Range9Delete90Store900Load/sync.Map-16 1.00 ± 0%
```