planner: support hint USE_CASCADES(true|false) to use/disuse cascades planner in a single query

go.mod

@@ -37,7 +37,7 @@ require (
 	github.com/pingcap/goleveldb v0.0.0-20191226122134-f82aafb29989
 	github.com/pingcap/kvproto v0.0.0-20200228095611-2cf9a243b8d5
 	github.com/pingcap/log v0.0.0-20200117041106-d28c14d3b1cd
-	github.com/pingcap/parser v0.0.0-20200305120128-bde9faa0df84
+	github.com/pingcap/parser v0.0.0-20200315112143-3dc646cd6b52
 	github.com/pingcap/pd/v4 v4.0.0-beta.1.0.20200305072537-61d9f9cc35d3
 	github.com/pingcap/sysutil v0.0.0-20200309085538-962fd285f3bb
 	github.com/pingcap/tidb-tools v4.0.0-beta.1.0.20200306084441-875bd09aa3d5+incompatible
@@ -66,7 +66,7 @@ require (
 	golang.org/x/sys v0.0.0-20200113162924-86b910548bc1
 	golang.org/x/text v0.3.2
 	golang.org/x/time v0.0.0-20190308202827-9d24e82272b4 // indirect
-	golang.org/x/tools v0.0.0-20200304193943-95d2e580d8eb
+	golang.org/x/tools v0.0.0-20200313205530-4303120df7d8
 	google.golang.org/grpc v1.25.1
 	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
 	gopkg.in/natefinch/lumberjack.v2 v2.0.0

go.sum

@@ -269,6 +269,8 @@ github.com/pingcap/log v0.0.0-20200117041106-d28c14d3b1cd h1:CV3VsP3Z02MVtdpTMfE
 github.com/pingcap/log v0.0.0-20200117041106-d28c14d3b1cd/go.mod h1:4rbK1p9ILyIfb6hU7OG2CiWSqMXnp3JMbiaVJ6mvoY8=
 github.com/pingcap/parser v0.0.0-20200305120128-bde9faa0df84 h1:u5FOwUw9muF8mBTZVV1dQhoAKiEo2Ci54CxN9XchEEY=
 github.com/pingcap/parser v0.0.0-20200305120128-bde9faa0df84/go.mod h1:9v0Edh8IbgjGYW2ArJr19E+bvL8zKahsFp+ixWeId+4=
+github.com/pingcap/parser v0.0.0-20200315112143-3dc646cd6b52 h1:L8N5zWQOrQyDdpX8n/xYkIe/U8IuL/HYCVK9maD1EsQ=
+github.com/pingcap/parser v0.0.0-20200315112143-3dc646cd6b52/go.mod h1:9v0Edh8IbgjGYW2ArJr19E+bvL8zKahsFp+ixWeId+4=
 github.com/pingcap/pd/v4 v4.0.0-beta.1.0.20200305072537-61d9f9cc35d3 h1:Yrp99FnjHAEuDrSBql2l0IqCtJX7KwJbTsD5hIArkvk=
 github.com/pingcap/pd/v4 v4.0.0-beta.1.0.20200305072537-61d9f9cc35d3/go.mod h1:25GfNw6+Jcr9kca5rtmTb4gKCJ4jOpow2zV2S9Dgafs=
 github.com/pingcap/sysutil v0.0.0-20200206130906-2bfa6dc40bcd/go.mod h1:EB/852NMQ+aRKioCpToQ94Wl7fktV+FNnxf3CX/TTXI=
@@ -370,6 +372,7 @@ github.com/urfave/negroni v0.3.0/go.mod h1:Meg73S6kFm/4PpbYdq35yYWoCZ9mS/YSx+lKn
 github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 h1:eY9dn8+vbi4tKz5Qo6v2eYzo7kUS51QINcR5jNpbZS8=
 github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2/go.mod h1:UETIi67q53MR2AWcXfiuqkDkRtnGDLqkBTpCHuJHxtU=
 github.com/yookoala/realpath v1.0.0/go.mod h1:gJJMA9wuX7AcqLy1+ffPatSCySA1FQ2S8Ya9AIoYBpE=
+github.com/yuin/goldmark v1.1.25/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 go.etcd.io/bbolt v1.3.3 h1:MUGmc65QhB3pIlaQ5bB4LwqSj6GIonVJXpZiaKNyaKk=
 go.etcd.io/bbolt v1.3.3/go.mod h1:IbVyRI1SCnLcuJnV2u8VeU0CEYM7e686BmAb1XKL+uU=
 go.etcd.io/etcd v0.0.0-20191023171146-3cf2f69b5738/go.mod h1:dnLIgRNXwCJa5e+c6mIZCrds/GIG4ncV9HhK5PX7jPg=
@@ -489,6 +492,8 @@ golang.org/x/tools v0.0.0-20200130002326-2f3ba24bd6e7/go.mod h1:TB2adYChydJhpapK
 golang.org/x/tools v0.0.0-20200301222351-066e0c02454c/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
 golang.org/x/tools v0.0.0-20200304193943-95d2e580d8eb h1:iKlO7ROJc6SttHKlxzwGytRtBUqX4VARrNTgP2YLX5M=
 golang.org/x/tools v0.0.0-20200304193943-95d2e580d8eb/go.mod h1:o4KQGtdN14AW+yjsvvwRTJJuXz8XRtIHtEnmAXLyFUw=
+golang.org/x/tools v0.0.0-20200313205530-4303120df7d8 h1:gkI/wGGwpcG5W4hLCzZNGxA4wzWBGGDStRI1MrjDl2Q=
+golang.org/x/tools v0.0.0-20200313205530-4303120df7d8/go.mod h1:Sl4aGygMT6LrqrWclx+PTx3U+LnKx/seiNR+3G19Ar8=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898 h1:/atklqdjdhuosWIl6AIbOeHJjicWYPqR9bpxqxYG2pA=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

planner/optimize.go

@@ -165,7 +165,7 @@ func optimize(ctx context.Context, sctx sessionctx.Context, node ast.Node, is in
 	}
 
 	// Handle the logical plan statement, use cascades planner if enabled.
-	if sctx.GetSessionVars().EnableCascadesPlanner {
+	if sctx.GetSessionVars().GetEnableCascadesPlanner() {
 		finalPlan, cost, err := cascades.DefaultOptimizer.FindBestPlan(sctx, logic)
 		return finalPlan, names, cost, err
 	}
@@ -297,8 +297,8 @@ func handleStmtHints(hints []*ast.TableOptimizerHint) (stmtHints stmtctx.StmtHin
 	if len(hints) == 0 {
 		return
 	}
-	var memoryQuotaHint, useToJAHint, maxExecutionTime *ast.TableOptimizerHint
-	var memoryQuotaHintCnt, useToJAHintCnt, noIndexMergeHintCnt, readReplicaHintCnt, maxExecutionTimeCnt int
+	var memoryQuotaHint, useToJAHint, useCascadesHint, maxExecutionTime *ast.TableOptimizerHint
+	var memoryQuotaHintCnt, useToJAHintCnt, useCascadesHintCnt, noIndexMergeHintCnt, readReplicaHintCnt, maxExecutionTimeCnt int
 	for _, hint := range hints {
 		switch hint.HintName.L {
 		case "memory_quota":
@@ -307,6 +307,9 @@ func handleStmtHints(hints []*ast.TableOptimizerHint) (stmtHints stmtctx.StmtHin
 		case "use_toja":
 			useToJAHint = hint
 			useToJAHintCnt++
+		case "use_cascades":
+			useCascadesHint = hint
+			useCascadesHintCnt++
 		case "no_index_merge":
 			noIndexMergeHintCnt++
 		case "read_consistent_replica":
@@ -344,6 +347,15 @@ func handleStmtHints(hints []*ast.TableOptimizerHint) (stmtHints stmtctx.StmtHin
 		stmtHints.HasAllowInSubqToJoinAndAggHint = true
 		stmtHints.AllowInSubqToJoinAndAgg = useToJAHint.HintData.(bool)
 	}
+	// Handle USE_CASCADES
+	if useCascadesHintCnt != 0 {
+		if useCascadesHintCnt > 1 {
+			warn := errors.Errorf("USE_CASCADES() is defined more than once, only the last definition takes effect: USE_CASCADES(%v)", useCascadesHint.HintData.(bool))
+			warns = append(warns, warn)
+		}
+		stmtHints.HasEnableCascadesPlannerHint = true
+		stmtHints.EnableCascadesPlanner = useCascadesHint.HintData.(bool)
+	}
 	// Handle NO_INDEX_MERGE
 	if noIndexMergeHintCnt != 0 {
 		if noIndexMergeHintCnt > 1 {

session/session_test.go

@@ -3053,6 +3053,18 @@ func (s *testSessionSuite2) TestStmtHints(c *C) {
 	c.Assert(tk.Se.GetSessionVars().StmtCtx.GetWarnings(), HasLen, 1)
 	c.Assert(tk.Se.GetSessionVars().GetAllowInSubqToJoinAndAgg(), IsTrue)
 
+	// Test USE_CASCADES hint
+	tk.Se.GetSessionVars().SetEnableCascadesPlanner(true)
+	tk.MustExec("select /*+ USE_CASCADES(false) */ 1;")
+	c.Assert(tk.Se.GetSessionVars().GetEnableCascadesPlanner(), IsFalse)
+	tk.Se.GetSessionVars().SetEnableCascadesPlanner(false)
+	tk.MustExec("select /*+ USE_CASCADES(true) */ 1;")
+	c.Assert(tk.Se.GetSessionVars().GetEnableCascadesPlanner(), IsTrue)
+	tk.MustExec("select /*+ USE_CASCADES(false), USE_CASCADES(true) */ 1;")
+	c.Assert(tk.Se.GetSessionVars().StmtCtx.GetWarnings(), HasLen, 1)
+	c.Assert(tk.Se.GetSessionVars().StmtCtx.GetWarnings()[0].Err.Error(), Equals, "USE_CASCADES() is defined more than once, only the last definition takes effect: USE_CASCADES(true)")
+	c.Assert(tk.Se.GetSessionVars().GetEnableCascadesPlanner(), IsTrue)
+
 	// Test READ_CONSISTENT_REPLICA hint
 	tk.Se.GetSessionVars().SetReplicaRead(kv.ReplicaReadLeader)
 	tk.MustExec("select /*+ READ_CONSISTENT_REPLICA() */ 1;")

sessionctx/stmtctx/stmtctx.go

@@ -153,12 +153,15 @@ type StmtHints struct {
 	ReplicaRead             byte
 	AllowInSubqToJoinAndAgg bool
 	NoIndexMergeHint        bool
+	// EnableCascadesPlanner is use cascades planner for a single query only.
+	EnableCascadesPlanner bool
 
 	// Hint flags
 	HasAllowInSubqToJoinAndAggHint bool
 	HasMemQuotaHint                bool
 	HasReplicaReadHint             bool
 	HasMaxExecutionTime            bool
+	HasEnableCascadesPlannerHint   bool
 }
 
 // GetNowTsCached getter for nowTs, if not set get now time and cache it

sessionctx/variable/session.go

@@ -732,6 +732,19 @@ func (s *SessionVars) SetAllowInSubqToJoinAndAgg(val bool) {
 	s.allowInSubqToJoinAndAgg = val
 }
 
+// GetEnableCascadesPlanner get EnableCascadesPlanner from sql hints and SessionVars.EnableCascadesPlanner.
+func (s *SessionVars) GetEnableCascadesPlanner() bool {
+	if s.StmtCtx.HasEnableCascadesPlannerHint {
+		return s.StmtCtx.EnableCascadesPlanner
+	}
+	return s.EnableCascadesPlanner
+}
+
+// SetEnableCascadesPlanner set SessionVars.EnableCascadesPlanner.
+func (s *SessionVars) SetEnableCascadesPlanner(val bool) {
+	s.EnableCascadesPlanner = val
+}
+
 // GetEnableIndexMerge get EnableIndexMerge from SessionVars.enableIndexMerge.
 func (s *SessionVars) GetEnableIndexMerge() bool {
 	return s.enableIndexMerge
@@ -1115,7 +1128,7 @@ func (s *SessionVars) SetSystemVar(name string, val string) error {
 	case TiDBEnableChunkRPC:
 		s.EnableChunkRPC = TiDBOptOn(val)
 	case TiDBEnableCascadesPlanner:
-		s.EnableCascadesPlanner = TiDBOptOn(val)
+		s.SetEnableCascadesPlanner(TiDBOptOn(val))
 	case TiDBOptimizerSelectivityLevel:
 		s.OptimizerSelectivityLevel = tidbOptPositiveInt32(val, DefTiDBOptimizerSelectivityLevel)
 	case TiDBEnableTablePartition: