hashring
Consistent hashing hashring implementation.
Overview
This is an implementation of the consistent hashing hashring data structure.
In general, consistent hashing is all about mapping objects from a very big set of values (e.g., request id) to objects from a quite small set (e.g., server address). The word "consistent" means that it can produce consistent mapping on different machines or processes without additional state exchange and communication.
For more theory about the subject please see this great document.
For more info about the package please read the docs.
The Why?
This is an approach for load distribution across servers which I found convinient to be used in a few projects I had worked on in the past.
I think it is good to implement it from scratch to synthesize all my experience working with it and share it with the community in hope it will help to build something good.
The key points of the package:
- Efficient concurrent read operations
- Correct handling of write operations (order of insertions on different processes doesn't matter; hash collisions are handled carefully).
Installation
go get github.com/gobwas/hashring
Usage
package main
import (
"strings"
"io"
"github.com/gobwas/hashring"
)
func main() {
var ring hashring.Ring
_ = ring.Insert(StringItem("server01"))
_ = ring.Insert(StringItem("server02"))
_ = ring.Insert(StringItem("server03"))
_ = ring.Insert(StringItem("server04"))
ring.Get(StringItem("user01")) // server04
ring.Get(StringItem("user02")) // server04
ring.Get(StringItem("user03")) // server02
ring.Get(StringItem("user04")) // server01
}
type StringItem string
func (s StringItem) WriteTo(w io.Writer) (int64, error) {
n, err := io.WriteString(w, string(s))
return int64(n), err
}
Contributing
If you find some bug or want to improve this package in any way feel free to file an issue to discuss your findings or ideas.
Debugging
Note that this package comes with built in debug tracing (which only takes place if you pass hashring_trace build tag, thanks to gtrace zero-cost tracing).
This means that you can make hashring to print out each meaningful step it does to understand better what's happening under the hood.
It also consumes hashring_debug build tag, which allows you to hook into hash calculation process and override the value it returns. For example, this was useful to test hash collisions.
