server/balancer: add scheduler and simplify schedule configs (#396)

The original balance configs are complicated and some of them are very
confusing, now we simplify them to make it more easy to understand.

We replace the concept of "balance" with "schedule". Balance means to
keep the resource balance, but we will introduce different kinds of
strategies in the future which may not balance, and balance is just one
kind of strategies to schedule resources between stores.

conf/config.toml

@@ -21,21 +21,16 @@ tso-save-interval = "3s"
 max-peer-count = 3
 
 
-[balance]
-min-capacity-used-ratio = 0.1
-max-capacity-used-ratio = 0.9
-max-leader-count = 10
-max-sending-snap-count = 3
-max-receiving-snap-count = 3
-max-applying-snap-count = 3
-max-diff-score-fraction = 0.1
-balance-interval = 30
-max-balance-count = 16
-max-balance-retry-per-loop = 10
-max-balance-count-per-loop = 3
-max-transfer-wait-count = 3
-max-peer-down-duration = "30m"
-max-store-down-duration = "10m"
+[schedule]
+min-region-count = 10
+min-leader-count = 10
+max-snapshot-count = 3
+min-balance-diff-ratio = 0.01
+max-store-down-duration = "30m"
+balance-interval = "30s"
+max-balance-count = 4
+max-balance-retry-per-loop = 4
+max-balance-count-per-loop = 1
 
 [metric]
 # prometheus client push interval, set "0s" to disable prometheus.

server/api/config.go

@@ -37,13 +37,13 @@ func (h *confHandler) Get(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *confHandler) Post(w http.ResponseWriter, r *http.Request) {
-	config := &server.BalanceConfig{}
+	config := &server.ScheduleConfig{}
 	err := readJSON(r.Body, config)
 	if err != nil {
 		h.rd.JSON(w, http.StatusInternalServerError, err.Error())
 		return
 	}
 
-	h.svr.SetBalanceConfig(*config)
+	h.svr.SetScheduleConfig(*config)
 	h.rd.JSON(w, http.StatusOK, nil)
 }