*: Enable distributed count with TiKV (#1312)

Push down count to TiKV

executor/builder.go

@@ -377,9 +377,6 @@ func (b *executorBuilder) buildAggregate(v *plan.Aggregate) Executor {
 		return nil
 	}
 	client := txn.GetClient()
-	if !client.SupportRequestType(kv.ReqTypeSelect, kv.ReqSubTypeAgg) {
-		return e
-	}
 	if len(v.GroupByItems) > 0 && !client.SupportRequestType(kv.ReqTypeSelect, kv.ReqSubTypeGroupBy) {
 		return e
 	}

kv/kv.go

@@ -111,8 +111,7 @@ const (
 
 	ReqSubTypeBasic   = 0
 	ReqSubTypeDesc    = 10000
-	ReqSubTypeAgg     = 10001
-	ReqSubTypeGroupBy = 10002
+	ReqSubTypeGroupBy = 10001
 )
 
 // KeyRange represents a range where StartKey <= key < EndKey.

store/localstore/local_client.go

@@ -39,7 +39,7 @@ func (c *dbClient) SupportRequestType(reqType, subType int64) bool {
 	switch reqType {
 	case kv.ReqTypeSelect:
 		switch subType {
-		case kv.ReqSubTypeAgg:
+		case kv.ReqSubTypeGroupBy:
 			return true
 		default:
 			return supportExpr(tipb.ExprType(subType))

store/tikv/coprocessor.go

@@ -37,7 +37,12 @@ type CopClient struct {
 func (c *CopClient) SupportRequestType(reqType, subType int64) bool {
 	switch reqType {
 	case kv.ReqTypeSelect:
-		return supportExpr(tipb.ExprType(subType))
+		switch subType {
+		case kv.ReqSubTypeGroupBy:
+			return true
+		default:
+			return supportExpr(tipb.ExprType(subType))
+		}
 	case kv.ReqTypeIndex:
 		switch subType {
 		case kv.ReqSubTypeDesc, kv.ReqSubTypeBasic:
@@ -58,6 +63,8 @@ func supportExpr(exprType tipb.ExprType) bool {
 		tipb.ExprType_In, tipb.ExprType_ValueList,
 		tipb.ExprType_Like, tipb.ExprType_Not:
 		return true
+	case tipb.ExprType_Count:
+		return true
 	case kv.ReqSubTypeDesc:
 		return true
 	default: