关于dubbo:聊聊dubbogo的ConsistentHashLoadBalance

序

本文次要钻研一下dubbo-go的ConsistentHashLoadBalance

ConsistentHashLoadBalance

dubbo-go-v1.4.2/cluster/loadbalance/consistent_hash.go

const (    // ConsistentHash ...    ConsistentHash = "consistenthash"    // HashNodes ...    HashNodes = "hash.nodes"    // HashArguments ...    HashArguments = "hash.arguments")var (    selectors = make(map[string]*ConsistentHashSelector)    re        = regexp.MustCompile(constant.COMMA_SPLIT_PATTERN))func init() {    extension.SetLoadbalance(ConsistentHash, NewConsistentHashLoadBalance)}// ConsistentHashLoadBalance ...type ConsistentHashLoadBalance struct {}// NewConsistentHashLoadBalance ...func NewConsistentHashLoadBalance() cluster.LoadBalance {    return &ConsistentHashLoadBalance{}}

ConsistentHashLoadBalance的init办法设置了名为consistenthash的ConsistentHashLoadBalance到extension中

Select

dubbo-go-v1.4.2/cluster/loadbalance/consistent_hash.go

// Select ...func (lb *ConsistentHashLoadBalance) Select(invokers []protocol.Invoker, invocation protocol.Invocation) protocol.Invoker {    methodName := invocation.MethodName()    key := invokers[0].GetUrl().ServiceKey() + "." + methodName    // hash the invokers    bs := make([]byte, 0)    for _, invoker := range invokers {        b, err := json.Marshal(invoker)        if err != nil {            return nil        }        bs = append(bs, b...)    }    hashCode := crc32.ChecksumIEEE(bs)    selector, ok := selectors[key]    if !ok || selector.hashCode != hashCode {        selectors[key] = newConsistentHashSelector(invokers, methodName, hashCode)        selector = selectors[key]    }    return selector.Select(invocation)}

Select办法遍历invokers挨个执行json.Marshal(invoker)，将bytes[]增加到bs中，之后通过crc32.ChecksumIEEE(bs)计算hashCode，而后比照selectors[key]的hashCode与计算出来的hashCode是否统一，不统一则通过newConsistentHashSelector从新设置一个，最初执行selector.Select(invocation)

ConsistentHashSelector

dubbo-go-v1.4.2/cluster/loadbalance/consistent_hash.go

// ConsistentHashSelector ...type ConsistentHashSelector struct {    hashCode        uint32    replicaNum      int    virtualInvokers map[uint32]protocol.Invoker    keys            Uint32Slice    argumentIndex   []int}

ConsistentHashSelector定义了hashCode、replicaNum、virtualInvokers、keys、argumentIndex属性

newConsistentHashSelector

dubbo-go-v1.4.2/cluster/loadbalance/consistent_hash.go

func newConsistentHashSelector(invokers []protocol.Invoker, methodName string,    hashCode uint32) *ConsistentHashSelector {    selector := &ConsistentHashSelector{}    selector.virtualInvokers = make(map[uint32]protocol.Invoker)    selector.hashCode = hashCode    url := invokers[0].GetUrl()    selector.replicaNum = int(url.GetMethodParamInt(methodName, HashNodes, 160))    indices := re.Split(url.GetMethodParam(methodName, HashArguments, "0"), -1)    for _, index := range indices {        i, err := strconv.Atoi(index)        if err != nil {            return nil        }        selector.argumentIndex = append(selector.argumentIndex, i)    }    for _, invoker := range invokers {        u := invoker.GetUrl()        address := u.Ip + ":" + u.Port        for i := 0; i < selector.replicaNum/4; i++ {            digest := md5.Sum([]byte(address + strconv.Itoa(i)))            for j := 0; j < 4; j++ {                key := selector.hash(digest, j)                selector.keys = append(selector.keys, key)                selector.virtualInvokers[key] = invoker            }        }    }    sort.Sort(selector.keys)    return selector}

newConsistentHashSelector办法实例化ConsistentHashSelector，并初始化virtualInvokers、hashCode、argumentIndex、keys、virtualInvokers属性

Select

dubbo-go-v1.4.2/cluster/loadbalance/consistent_hash.go

// Select ...func (c *ConsistentHashSelector) Select(invocation protocol.Invocation) protocol.Invoker {    key := c.toKey(invocation.Arguments())    digest := md5.Sum([]byte(key))    return c.selectForKey(c.hash(digest, 0))}func (c *ConsistentHashSelector) toKey(args []interface{}) string {    var sb strings.Builder    for i := range c.argumentIndex {        if i >= 0 && i < len(args) {            fmt.Fprint(&sb, args[i].(string))        }    }    return sb.String()}func (c *ConsistentHashSelector) selectForKey(hash uint32) protocol.Invoker {    idx := sort.Search(len(c.keys), func(i int) bool {        return c.keys[i] >= hash    })    if idx == len(c.keys) {        idx = 0    }    return c.virtualInvokers[c.keys[idx]]}func (c *ConsistentHashSelector) hash(digest [16]byte, i int) uint32 {    return uint32((digest[3+i*4]&0xFF)<<24) | uint32((digest[2+i*4]&0xFF)<<16) |        uint32((digest[1+i*4]&0xFF)<<8) | uint32(digest[i*4]&0xFF)&0xFFFFFFF}

Select办法通过c.toKey(invocation.Arguments())获取key，再通过md5.Sum([]byte(key))计算digest，最初通过c.selectForKey(c.hash(digest, 0))选取Invoker

小结

ConsistentHashLoadBalance的Select办法遍历invokers挨个执行json.Marshal(invoker)，将bytes[]增加到bs中，之后通过crc32.ChecksumIEEE(bs)计算hashCode，而后比照selectors[key]的hashCode与计算出来的hashCode是否统一，不统一则通过newConsistentHashSelector从新设置一个，最初执行selector.Select(invocation)

doc

consistent_hash