dubbo-go中ConsistentHashLoadBalance的用法

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序

本文主要研究一下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方法设置了名为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方法遍历invokers挨个执行json.Marshal(invoker)，将bytes[]添加到bs中，之后通过crc32.ChecksumIEEE(bs)计算hashCode，然后对比selectors[key]的hashCode与计算出来的hashCode是否一致，不一致则通过newConsistentHashSelector重新设置一个，最后执行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方法实例化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方法通过c.toKey(invocation.Arguments())获取key，再通过md5.Sum([]byte(key))计算digest，最后通过c.selectForKey(c.hash(digest, 0))选取Invoker

小结

ConsistentHashLoadBalance的Select方法遍历invokers挨个执行json.Marshal(invoker)，将bytes[]添加到bs中，之后通过crc32.ChecksumIEEE(bs)计算hashCode，然后对比selectors[key]的hashCode与计算出来的hashCode是否一致，不一致则通过newConsistentHashSelector重新设置一个，最后执行selector.Select(invocation)

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