# 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。 1. 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()) } ~~~ 2. 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})) } ~~~ 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()) } ~~~ 4. 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})) } ~~~ 5. 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()) } ~~~ 6. 自定义负载策略 实现GroupPolicy接口来实现自定义负载策略。 ~~~ type GroupPolicy interface { Slave(*EngineGroup) *Engine } ~~~