planner: add cascades wrapper for integrating cascades into current logical optimization phase.

pkg/planner/cascades/BUILD.bazel

@@ -0,0 +1,24 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "cascades",
+    srcs = ["cascades.go"],
+    importpath = "github.com/pingcap/tidb/pkg/planner/cascades",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/planner/cascades/base",
+        "//pkg/planner/cascades/base/cascadesctx",
+        "//pkg/planner/cascades/memo",
+        "//pkg/planner/cascades/task",
+        "//pkg/planner/core/base",
+        "//pkg/util/intest",
+    ],
+)
+
+go_test(
+    name = "cascades_test",
+    timeout = "short",
+    srcs = ["cascades_test.go"],
+    flaky = True,
+    deps = ["//pkg/testkit"],
+)

pkg/planner/cascades/base/cascadesctx/cascades_ctx.go

@@ -19,12 +19,12 @@ import (
 	"github.com/pingcap/tidb/pkg/planner/cascades/memo"
 )
 
-// CascadesContext define the cascades context as interface, since it will be defined
+// Context define the cascades context as interface, since it will be defined
 // in cascades pkg, which ref task pkg with no doubt.
 // while in the task pkg, the concrete task need receive cascades context as its
 // constructing args, which will lead an import cycle.
 // so that's why we separate it out of base pkg.
-type CascadesContext interface {
+type Context interface {
 	Destroy()
 	GetScheduler() base.Scheduler
 	PushTask(task base.Task)

pkg/planner/cascades/cascades.go

@@ -0,0 +1,105 @@
+// Copyright 2024 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cascades
+
+import (
+	"github.com/pingcap/tidb/pkg/planner/cascades/base"
+	"github.com/pingcap/tidb/pkg/planner/cascades/base/cascadesctx"
+	"github.com/pingcap/tidb/pkg/planner/cascades/memo"
+	"github.com/pingcap/tidb/pkg/planner/cascades/task"
+	corebase "github.com/pingcap/tidb/pkg/planner/core/base"
+	"github.com/pingcap/tidb/pkg/util/intest"
+)
+
+// Optimizer is a basic cascades search framework portal, driven by Context.
+type Optimizer struct {
+	logic corebase.LogicalPlan
+	ctx   cascadesctx.Context
+}
+
+// NewCascades return a new cascades obj for logical alternative searching.
+func NewCascades(lp corebase.LogicalPlan) (*Optimizer, error) {
+	cas := &Optimizer{
+		logic: lp,
+		ctx:   NewContext(lp.SCtx()),
+	}
+	ge, err := cas.ctx.GetMemo().Init(lp)
+	intest.Assert(err == nil)
+	intest.Assert(ge != nil)
+	if err != nil {
+		return nil, err
+	}
+	cas.ctx.GetScheduler().PushTask(task.NewOptGroupTask(cas.ctx, ge.GetGroup()))
+	return cas, err
+}
+
+// Execute run the yams search flow inside, returns error if it happened.
+func (c *Optimizer) Execute() error {
+	return c.ctx.GetScheduler().ExecuteTasks()
+}
+
+// Destroy clean and reset basic elements inside.
+func (c *Optimizer) Destroy() {
+	c.ctx.Destroy()
+}
+
+// GetMemo returns the memo structure inside cascades.
+func (c *Optimizer) GetMemo() *memo.Memo {
+	return c.ctx.GetMemo()
+}
+
+// Context includes all the context stuff when go through memo optimizing.
+type Context struct {
+	// pctx variable awareness.
+	pctx corebase.PlanContext
+	// memo management.
+	mm *memo.Memo
+	// task pool management.
+	scheduler base.Scheduler
+}
+
+// NewContext returns a new memo context responsible for manage all the stuff in cascades opt.
+func NewContext(pctx corebase.PlanContext) *Context {
+	return &Context{
+		pctx: pctx,
+		// memo init with capacity.
+		mm: memo.NewMemo(pctx.GetSessionVars().StmtCtx.OperatorNum),
+		// task pool management.
+		scheduler: task.NewSimpleTaskScheduler(),
+	}
+}
+
+// Destroy the memo context, which will clean the resource allocated during this phase.
+func (c *Context) Destroy() {
+	// when a memo optimizing phase is done for a session,
+	// we should put the stack back and clean the memo.
+	c.mm.Destroy()
+	c.scheduler.Destroy()
+}
+
+// GetScheduler return the stack inside this memo context.
+func (c *Context) GetScheduler() base.Scheduler {
+	return c.scheduler
+}
+
+// PushTask puts a task into the stack structure inside.
+func (c *Context) PushTask(task base.Task) {
+	c.scheduler.PushTask(task)
+}
+
+// GetMemo returns the basic memo structure.
+func (c *Context) GetMemo() *memo.Memo {
+	return c.mm
+}

pkg/planner/cascades/cascades_test.go

@@ -0,0 +1,38 @@
+// Copyright 2024 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cascades_test
+
+import (
+	"testing"
+
+	"github.com/pingcap/tidb/pkg/testkit"
+)
+
+func TestCascadesDrive(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.Session().GetSessionVars().SetEnableCascadesPlanner(true)
+
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1")
+	tk.MustExec("create table t1(a int not null, b int not null, key(a,b))")
+	tk.MustExec("insert into t1 values(1,1),(1,2),(2,1),(2,2),(1,1)")
+
+	// simple select for quick debug of memo, the normal test case is in tests/planner/cascades/integration.test.
+	tk.MustQuery("select 1").Check(testkit.Rows("1"))
+	tk.MustQuery("explain select 1").Check(testkit.Rows(""+
+		"Projection_3 1.00 root  1->Column#1",
+		"└─TableDual_4 1.00 root  rows:1"))
+}

pkg/planner/cascades/memo/memo.go

@@ -70,6 +70,17 @@ func NewMemo(caps ...uint64) *Memo {
 	}
 }
 
+// Destroy indicates that when stack itself is useless like in the end of optimizing phase, we can destroy ourselves.
+func (mm *Memo) Destroy() {
+	// when a memo itself is useless, we can clean itself actively.
+	mm.groupIDGen.id = 0
+	mm.rootGroup = nil
+	mm.groups.Init()
+	clear(mm.groupID2Group)
+	mm.hash2GlobalGroupExpr.Clear()
+	mm.hasher.Reset()
+}
+
 // GetHasher gets a hasher from the memo that ready to use.
 func (mm *Memo) GetHasher() base2.Hasher {
 	mm.hasher.Reset()
@@ -329,6 +340,25 @@ type IteratorLP struct {
 	traceID int
 }
 
+// NewIterator new a logical plan iterator from current memo based on its root group.
+func (mm *Memo) NewIterator() *IteratorLP {
+	return &IteratorLP{
+		root:      mm.rootGroup,
+		stackInfo: make([]*list.Element, 0, mm.groups.Len()),
+		traceID:   -1,
+	}
+}
+
+// Each iterator all logical plan from current memo group.
+func (it *IteratorLP) Each(f func(base.LogicalPlan) bool) {
+	cur := it.Next()
+	for ; cur != nil; cur = it.Next() {
+		if !f(cur) {
+			break
+		}
+	}
+}
+
 // Next return valid logical plan implied in memo without duplication.
 func (it *IteratorLP) Next() (logic base.LogicalPlan) {
 	for {

pkg/planner/cascades/task/base.go

@@ -21,7 +21,7 @@ import (
 
 // BaseTask is base task wrapper structure for encapsulating basic things.
 type BaseTask struct {
-	ctx cascadesctx.CascadesContext
+	ctx cascadesctx.Context
 }
 
 // Push pushes a new task into inside stack.

pkg/planner/cascades/task/task_apply_rule.go

@@ -84,7 +84,7 @@ type ApplyRuleTask struct {
 }
 
 // NewApplyRuleTask return a new apply rule task.
-func NewApplyRuleTask(ctx cascadesctx.CascadesContext, gE *memo.GroupExpression, r rule.Rule) *ApplyRuleTask {
+func NewApplyRuleTask(ctx cascadesctx.Context, gE *memo.GroupExpression, r rule.Rule) *ApplyRuleTask {
 	return &ApplyRuleTask{
 		BaseTask: BaseTask{
 			ctx: ctx,

pkg/planner/cascades/task/task_opt_group.go

@@ -31,7 +31,7 @@ type OptGroupTask struct {
 }
 
 // NewOptGroupTask returns a new optimizing group task.
-func NewOptGroupTask(ctx cascadesctx.CascadesContext, g *memo.Group) base.Task {
+func NewOptGroupTask(ctx cascadesctx.Context, g *memo.Group) base.Task {
 	return &OptGroupTask{BaseTask: BaseTask{
 		ctx: ctx,
 	}, group: g}

pkg/planner/cascades/task/task_opt_group_expression.go

@@ -33,7 +33,7 @@ type OptGroupExpressionTask struct {
 }
 
 // NewOptGroupExpressionTask return a targeting optimizing group expression task.
-func NewOptGroupExpressionTask(ctx cascadesctx.CascadesContext, ge *memo.GroupExpression) *OptGroupExpressionTask {
+func NewOptGroupExpressionTask(ctx cascadesctx.Context, ge *memo.GroupExpression) *OptGroupExpressionTask {
 	return &OptGroupExpressionTask{
 		BaseTask:        BaseTask{ctx: ctx},
 		groupExpression: ge,

pkg/planner/core/BUILD.bazel

@@ -120,6 +120,7 @@ go_library(
         "//pkg/parser/terror",
         "//pkg/parser/types",
         "//pkg/planner/cardinality",
+        "//pkg/planner/cascades",
         "//pkg/planner/cascades/base",
         "//pkg/planner/core/base",
         "//pkg/planner/core/cost",

pkg/planner/core/optimizer.go

@@ -38,6 +38,7 @@ import (
 	"github.com/pingcap/tidb/pkg/parser/auth"
 	pmodel "github.com/pingcap/tidb/pkg/parser/model"
 	"github.com/pingcap/tidb/pkg/parser/mysql"
+	"github.com/pingcap/tidb/pkg/planner/cascades"
 	"github.com/pingcap/tidb/pkg/planner/core/base"
 	"github.com/pingcap/tidb/pkg/planner/core/operator/logicalop"
 	"github.com/pingcap/tidb/pkg/planner/core/operator/physicalop"
@@ -275,18 +276,41 @@ func CascadesOptimize(ctx context.Context, sctx base.PlanContext, flag uint64, l
 	if !AllowCartesianProduct.Load() && existsCartesianProduct(logic) {
 		return nil, nil, 0, errors.Trace(plannererrors.ErrCartesianProductUnsupported)
 	}
-	planCounter := base.PlanCounterTp(sessVars.StmtCtx.StmtHints.ForceNthPlan)
-	if planCounter == 0 {
-		planCounter = -1
-	}
-	// todo: add cascadesOptimize(logic)
 
-	physical, cost, err := physicalOptimize(logic, &planCounter)
+	var cas *cascades.Optimizer
+	if cas, err = cascades.NewCascades(logic); err == nil {
+		defer cas.Destroy()
+		err = cas.Execute()
+	}
+	if err != nil {
+		return nil, nil, 0, err
+	}
+	var (
+		physical base.PhysicalPlan
+		cost     = math.MaxFloat64
+	)
+	// At current phase, cascades just iterate every logic plan out for feeding physicalOptimize.
+	// TODO: In the near future, physicalOptimize will be refactored as receiving *Group as param directly.
+	cas.GetMemo().NewIterator().Each(func(oneLogic base.LogicalPlan) bool {
+		planCounter := base.PlanCounterTp(sessVars.StmtCtx.StmtHints.ForceNthPlan)
+		if planCounter == 0 {
+			planCounter = -1
+		}
+		tmpPhysical, tmpCost, tmpErr := physicalOptimize(oneLogic, &planCounter)
+		if tmpErr != nil {
+			err = tmpErr
+			return false
+		}
+		if tmpCost < cost {
+			physical = tmpPhysical
+		}
+		return true
+	})
 	if err != nil {
 		return nil, nil, 0, err
 	}
-	finalPlan := postOptimize(ctx, sctx, physical)
 
+	finalPlan := postOptimize(ctx, sctx, physical)
 	if sessVars.StmtCtx.EnableOptimizerCETrace {
 		refineCETrace(sctx)
 	}