Documentation ¶
Overview ¶
Package consistent provides a consistent hashing function.
Consistent hashing is often used to distribute requests to a changing set of servers. For example, say you have some cache servers cacheA, cacheB, and cacheC. You want to decide which cache server to use to look up information on a user.
You could use a typical hash table and hash the user id to one of cacheA, cacheB, or cacheC. But with a typical hash table, if you add or remove a server, almost all keys will get remapped to different results, which basically could bring your service to a grinding halt while the caches get rebuilt.
With a consistent hash, adding or removing a server drastically reduces the number of keys that get remapped.
Read more about consistent hashing on wikipedia: http://en.wikipedia.org/wiki/Consistent_hashing
Index ¶
- Variables
- type Consistent
- func (c *Consistent) Add(elt string)
- func (c *Consistent) Get(name string) (string, error)
- func (c *Consistent) GetN(name string, n int) ([]string, error)
- func (c *Consistent) GetTwo(name string) (string, string, error)
- func (c *Consistent) Members() []string
- func (c *Consistent) Remove(elt string)
- func (c *Consistent) Set(elts []string)
Examples ¶
Constants ¶
This section is empty.
Variables ¶
var ErrEmptyCircle = errors.New("empty circle")
ErrEmptyCircle is the error returned when trying to get an element when nothing has been added to hash.
Functions ¶
This section is empty.
Types ¶
type Consistent ¶
type Consistent struct { NumberOfReplicas int UseFnv bool sync.RWMutex // contains filtered or unexported fields }
Consistent holds the information about the members of the consistent hash circle.
func New ¶
func New() *Consistent
New creates a new Consistent object with a default setting of 20 replicas for each entry.
To change the number of replicas, set NumberOfReplicas before adding entries.
Example ¶
package main import ( "fmt" "log" "github.com/ljfuyuan/consistent" ) func main() { c := consistent.New() c.Add("cacheA") c.Add("cacheB") c.Add("cacheC") users := []string{"user_mcnulty", "user_bunk", "user_omar", "user_bunny", "user_stringer"} for _, u := range users { server, err := c.Get(u) if err != nil { log.Fatal(err) } fmt.Printf("%s => %s\n", u, server) } }
Output: user_mcnulty => cacheA user_bunk => cacheA user_omar => cacheA user_bunny => cacheC user_stringer => cacheC
func NewWithFnv ¶
func NewWithFnv(replicas int) *Consistent
func (*Consistent) Add ¶
func (c *Consistent) Add(elt string)
Add inserts a string element in the consistent hash.
func (*Consistent) Get ¶
func (c *Consistent) Get(name string) (string, error)
Get returns an element close to where name hashes to in the circle.
func (*Consistent) GetN ¶
func (c *Consistent) GetN(name string, n int) ([]string, error)
GetN returns the N closest distinct elements to the name input in the circle.
func (*Consistent) GetTwo ¶
func (c *Consistent) GetTwo(name string) (string, string, error)
GetTwo returns the two closest distinct elements to the name input in the circle.
func (*Consistent) Members ¶
func (c *Consistent) Members() []string
func (*Consistent) Remove ¶
func (c *Consistent) Remove(elt string)
Remove removes an element from the hash.
func (*Consistent) Set ¶
func (c *Consistent) Set(elts []string)
Set sets all the elements in the hash. If there are existing elements not present in elts, they will be removed.