GO-REDIS some advanced usage

1 Introduction

Speaking Golang of Redis library, probably the most used
redigo  and  Go-Redis . Which  redigo does not support access to the cluster.
This article would like to talk about go-redis two Advanced Usage

2. Enable access to the Slave Node of Cluster

In a relatively high load of Redis Cluster, if allowed to read will greatly improve the handling capacity of the slave node cluster.

Open access to the Slave nodes affected by the following three parameters

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 Logical nodes selected as follows

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
}

• If ReadOnly = true, select onlySlave Node
• If ReadOnly = true and RouteByLatency = true from the slotcorresponding Master Node and  Slave Nodeselection, selection policy is: Select PING delay the lowest node
• If ReadOnly = true and RouteRandomly = true from the slotcorresponding Master Node and  Slave Nodeselection, selection policy: random selection

3. Use the pipeline function in a clustered mode

Redis principle function of the pipeline is a one-time Client will be sent to multiple redis command Redis Server, reducing the IO overhead of each command are transmitted. While reducing the number of system calls, and thus enhance the overall handling capacity.

We in the main - from Redis mode, pipeline function should be used a lot, but in Cluster mode, it is estimated that few people used.
We know redis cluster default allocated 16,384 slot, when we set a key, will use CRC16 algorithm to get modulo belongs slot, then the node will be assigned to this key hash slot interval, the specific algorithm is: CRC16 (key )% 16384. If we use the pipeline function, multiple commands in a batch contained, key each command involved may belong to differentslot

go-redis To solve this problem, three steps
source can read  defaultProcessPipeline
. 1) will be calculated command belongs slot, according to slotchoose the right Cluster Node
) with a 2 to Cluster Node all command, in a batch transmission (concurrent operation)
3) reception result

Note: This go-redis order is simple, each command can only involve a key, or you may receive the following error

err CROSSSLOT Keys in request don't hash to the same slot

That go-redis does not support a similar  MGET command usage

A simple example

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)
    }
}