# 負載策略 通過xorm.NewEngineGroup創建EngineGroup時，第三個參數為policies，我們可以通過該參數來指定Slave訪問的負載策略。如創建EngineGroup時未指定，則默認使用輪詢的負載策略。 xorm中內置五種負載策略，分別為隨機訪問負載策略，權重隨機訪問負載策略，輪詢訪問負載策略，權重輪詢訪問負載策略和最小連接數訪問負載策略。開發者也可以通過實現GroupPolicy接口，來實現自定義負載策略。 1. 隨機訪問負載策略 ~~~ 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. 權重隨機訪問負載策略 ~~~ 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 //此時設置的test1數據庫和test2數據庫的隨機訪問權重為2和3 eg, err = xorm.NewEngineGroup("postgres", conns, xorm.WeightRandomPolicy([]int{2, 3})) } ~~~ 3. 輪詢訪問負載策略 ~~~ 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. 權重輪詢訪問負載策略 ~~~ 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 //此時設置的test1數據庫和test2數據庫的輪詢訪問權重為2和3 eg, err = xorm.NewEngineGroup("postgres", conns, xorm.WeightRoundRobinPolicy([]int{2, 3})) } ~~~ 5. 最小連接數訪問負載策略 ~~~ 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. 自定義負載策略 實現GroupPolicy接口來實現自定義負載策略。 ~~~ type GroupPolicy interface { Slave(*EngineGroup) *Engine } ~~~