聊聊dubbogo的ConsistentHashLoadBalance

  • Z时代
  • 2024-01-10
  • 分类：综合

编程

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)

doc

  • consistent_hash

以上是 聊聊dubbogo的ConsistentHashLoadBalance 的全部内容， 来源链接： utcz.com/z/519275.html

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