聊聊go-redis的一些高级用法
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1. 前言
说到Golang的Redis库，用到最多的恐怕是
redigo 和 go-redis。其中 redigo 不支持对集群的访问。
本文想聊聊go-redis 2个高级用法
2. 开启对Cluster中Slave Node的访问
在一个负载比较高的Redis Cluster中，如果允许对slave节点进行读操作将极大的提高集群的吞吐能力。
开启对Slave 节点的访问，受以下3个参数的影响
type ClusterOptions struct {
// Enables read-only commands on slave nodes.
ReadOnly bool
// Allows routing read-only commands to the closest master or slave node.
// It automatically enables ReadOnly.
RouteByLatency bool
// Allows routing read-only commands to the random master or slave node.
// It automatically enables ReadOnly.
RouteRandomly bool
...
}
go-redis 选择节点的逻辑如下
func (c *ClusterClient) cmdSlotAndNode(cmd Cmder) (int, *clusterNode, error) {
state, err := c.state.Get()
if err != nil {
return 0, nil, err
}
cmdInfo := c.cmdInfo(cmd.Name())
slot := cmdSlot(cmd, cmdFirstKeyPos(cmd, cmdInfo))
if c.opt.ReadOnly && cmdInfo != nil && cmdInfo.ReadOnly {
if c.opt.RouteByLatency {
node, err := state.slotClosestNode(slot)
return slot, node, err
}
if c.opt.RouteRandomly {
node := state.slotRandomNode(slot)
return slot, node, nil
}
node, err := state.slotSlaveNode(slot)
return slot, node, err
}
node, err := state.slotMasterNode(slot)
return slot, node, err
}
- 如果ReadOnly = true，只选择
Slave Node - 如果ReadOnly = true 且 RouteByLatency = true 将从
slot对应的Master Node和Slave Node选择，选择策略为: 选择PING延迟最低的节点 - 如果ReadOnly = true 且 RouteRandomly = true 将从
slot对应的Master Node和Slave Node选择，选择策略为:随机选择
3. 在集群模式下使用pipeline功能
Redis的pipeline功能的原理是 Client通过一次性将多条redis命令发往Redis Server，减少了每条命令分别传输的IO开销。同时减少了系统调用的次数，因此提升了整体的吞吐能力。
我们在主-从模式的Redis中，pipeline功能应该用的很多，但是Cluster模式下，估计还没有几个人用过。
我们知道 redis cluster 默认分配了 16384 个slot，当我们set一个key 时，会用CRC16算法来取模得到所属的slot，然后将这个key 分到哈希槽区间的节点上，具体算法就是：CRC16(key) % 16384。如果我们使用pipeline功能，一个批次中包含的多条命令，每条命令涉及的key可能属于不同的slot
go-redis 为了解决这个问题, 分为3步
源码可以阅读 defaultProcessPipeline
1) 将计算command 所属的slot, 根据slot选择合适的Cluster Node
2）将同一个Cluster Node 的所有command，放在一个批次中发送（并发操作）
3）接收结果
注意：这里go-redis 为了处理简单，每个command 只能涉及一个key, 否则你可能会收到如下错误
err CROSSSLOT Keys in request don't hash to the same slot
也就是说go-redis不支持类似 MGET 命令的用法
一个简单的例子
package main
import (
"github.com/go-redis/redis"
"fmt"
)
func main() {
client := redis.NewClusterClient(&redis.ClusterOptions{
Addrs: []string{"192.168.120.110:6380", "192.168.120.111:6380"},
ReadOnly: true,
RouteRandomly: true,
})
pipe := client.Pipeline()
pipe.HGetAll("1371648200")
pipe.HGetAll("1371648300")
pipe.HGetAll("1371648400")
cmders, err := pipe.Exec()
if err != nil {
fmt.Println("err", err)
}
for _, cmder := range cmders {
cmd := cmder.(*redis.StringStringMapCmd)
strMap, err := cmd.Result()
if err != nil {
fmt.Println("err", err)
}
fmt.Println("strMap", strMap)
}
}
后记:
2022年09月16日 需要注意的点
主从模式下，一组只读副本(多个slave实例)如果使用的是高可用域名，由于域名解析的结果在进程中会缓存，因此所有请求可能都被发往了同一个实例。
你需要使用Dialer参数，它会在每次创建连接时被调用。
options := redis.Options{
Addr: "movie.vearne.redis:18429",
Password: "xxxxxx",
// Dialer creates new network connection and has priority over
// Network and Addr options.
Dialer: func(ctx context.Context, network, addr string) (net.Conn, error) {
r := &net.Resolver{}
host, port, err := net.SplitHostPort(addr)
if err != nil {
return nil, err
}
ips, err := r.LookupHost(context.Background(), host)
if err != nil {
return nil, err
}
ip := ips[rand.Intn(len(ips))]
netDialer := &net.Dialer{
Timeout: 10 * time.Second,
KeepAlive: 1 * time.Minute,
}
fmt.Println("addr", net.JoinHostPort(ip, port))
return netDialer.DialContext(ctx, network, net.JoinHostPort(ip, port))
},
}
client := redis.NewClient(&options)
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