1. 负载策略

通过xorm.NewEngineGroup创建EngineGroup时，第三个参数为policies，我们可以通过该参数来指定Slave访问的负载策略。如创建EngineGroup时未指定，则默认使用轮询的负载策略。

xorm中内置五种负载策略，分别为随机访问负载策略，权重随机访问负载策略，轮询访问负载策略，权重轮询访问负载策略和最小连接数访问负载策略。开发者也可以通过实现GroupPolicy接口，来实现自定义负载策略。

• 随机访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.RandomPolicy())
}

• 权重随机访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    //此时设置的test1数据库和test2数据库的随机访问权重为2和3
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.WeightRandomPolicy([]int{2, 3}))
}

• 轮询访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.RoundRobinPolicy())
}

• 权重轮询访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    //此时设置的test1数据库和test2数据库的轮询访问权重为2和3
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.WeightRoundRobinPolicy([]int{2, 3}))
}

• 最小连接数访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.LeastConnPolicy())
}

• 自定义负载策略

你也可以通过实现 GroupPolicy 接口来实现自定义负载策略。

type GroupPolicy interface {
    Slave(*EngineGroup) *Engine
}