planner: support the Group and GroupExpr for the cascades planner (#7917

)

planner/cascades/group.go

@@ -0,0 +1,72 @@
+// Copyright 2018 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cascades
+
+import (
+	"container/list"
+	"fmt"
+)
+
+// Group is short for expression group, which is used to store all the
+// logically equivalent expressions. It's a set of GroupExpr.
+type Group struct {
+	equivalents  *list.List
+	fingerprints map[string]*list.Element
+
+	explored        bool
+	selfFingerprint string
+}
+
+// NewGroup creates a new Group.
+func NewGroup(e *GroupExpr) *Group {
+	g := &Group{
+		equivalents:  list.New(),
+		fingerprints: make(map[string]*list.Element),
+	}
+	g.Insert(e)
+	return g
+}
+
+// FingerPrint returns the unique fingerprint of the group.
+func (g *Group) FingerPrint() string {
+	if g.selfFingerprint == "" {
+		g.selfFingerprint = fmt.Sprintf("%p", g)
+	}
+	return g.selfFingerprint
+}
+
+// Insert a nonexistent group expression.
+func (g *Group) Insert(e *GroupExpr) bool {
+	if g.Exists(e) {
+		return false
+	}
+	newEquiv := g.equivalents.PushBack(e)
+	g.fingerprints[e.FingerPrint()] = newEquiv
+	return true
+}
+
+// Delete an existing group expression.
+func (g *Group) Delete(e *GroupExpr) {
+	fingerprint := e.FingerPrint()
+	if equiv, ok := g.fingerprints[fingerprint]; ok {
+		g.equivalents.Remove(equiv)
+		delete(g.fingerprints, fingerprint)
+	}
+}
+
+// Exists checks whether a group expression existed in a Group.
+func (g *Group) Exists(e *GroupExpr) bool {
+	_, ok := g.fingerprints[e.FingerPrint()]
+	return ok
+}

planner/cascades/group_expr.go

@@ -0,0 +1,53 @@
+// Copyright 2018 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cascades
+
+import (
+	"fmt"
+
+	plannercore "github.com/pingcap/tidb/planner/core"
+)
+
+// GroupExpr is used to store all the logically equivalent expressions which
+// have the same root operator. Different from a normal expression, the
+// children of a group expression are expression Groups, not expressions.
+// Another property of group expression is that the child group references will
+// never be changed once the group expression is created.
+type GroupExpr struct {
+	exprNode plannercore.LogicalPlan
+	children []*Group
+	explored bool
+
+	selfFingerprint string
+}
+
+// NewGroupExpr creates a GroupExpr based on a logical plan node.
+func NewGroupExpr(node plannercore.LogicalPlan) *GroupExpr {
+	return &GroupExpr{
+		exprNode: node,
+		children: nil,
+		explored: false,
+	}
+}
+
+// FingerPrint gets the unique fingerprint of the group expression.
+func (e *GroupExpr) FingerPrint() string {
+	if e.selfFingerprint == "" {
+		e.selfFingerprint = fmt.Sprintf("%v", e.exprNode.ID())
+		for i := range e.children {
+			e.selfFingerprint += e.children[i].FingerPrint()
+		}
+	}
+	return e.selfFingerprint
+}

planner/cascades/group_expr_test.go

@@ -0,0 +1,35 @@
+// Copyright 2018 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cascades
+
+import (
+	. "github.com/pingcap/check"
+	plannercore "github.com/pingcap/tidb/planner/core"
+)
+
+func (s *testCascadesSuite) TestNewGroupExpr(c *C) {
+	p := &plannercore.LogicalLimit{}
+	expr := NewGroupExpr(p)
+	c.Assert(expr.exprNode, Equals, p)
+	c.Assert(expr.children, IsNil)
+	c.Assert(expr.explored, IsFalse)
+}
+
+func (s *testCascadesSuite) TestGroupExprFingerprint(c *C) {
+	p := &plannercore.LogicalLimit{}
+	expr := NewGroupExpr(p)
+
+	// we haven't set the id of the created LogicalLimit, so the result is 0.
+	c.Assert(expr.FingerPrint(), Equals, "0")
+}

planner/cascades/group_test.go

@@ -0,0 +1,87 @@
+// Copyright 2018 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cascades
+
+import (
+	"testing"
+
+	. "github.com/pingcap/check"
+	plannercore "github.com/pingcap/tidb/planner/core"
+	"github.com/pingcap/tidb/sessionctx"
+	"github.com/pingcap/tidb/util/mock"
+	"github.com/pingcap/tidb/util/testleak"
+)
+
+func TestT(t *testing.T) {
+	CustomVerboseFlag = true
+	TestingT(t)
+}
+
+var _ = Suite(&testCascadesSuite{})
+
+type testCascadesSuite struct {
+	sctx sessionctx.Context
+}
+
+func (s *testCascadesSuite) SetUpSuite(c *C) {
+	testleak.BeforeTest()
+	s.sctx = mock.NewContext()
+}
+
+func (s *testCascadesSuite) TearDownSuite(c *C) {
+	testleak.AfterTest(c)()
+}
+
+func (s *testCascadesSuite) TestNewGroup(c *C) {
+	p := &plannercore.LogicalLimit{}
+	expr := NewGroupExpr(p)
+	g := NewGroup(expr)
+
+	c.Assert(g.equivalents.Len(), Equals, 1)
+	c.Assert(g.equivalents.Front().Value.(*GroupExpr), Equals, expr)
+	c.Assert(len(g.fingerprints), Equals, 1)
+	c.Assert(g.explored, IsFalse)
+}
+
+func (s *testCascadesSuite) TestGroupInsert(c *C) {
+	p := &plannercore.LogicalLimit{}
+	expr := NewGroupExpr(p)
+	g := NewGroup(expr)
+	c.Assert(g.Insert(expr), IsFalse)
+	expr.selfFingerprint = "1"
+	c.Assert(g.Insert(expr), IsTrue)
+}
+
+func (s *testCascadesSuite) TestGroupDelete(c *C) {
+	p := &plannercore.LogicalLimit{}
+	expr := NewGroupExpr(p)
+	g := NewGroup(expr)
+	c.Assert(g.equivalents.Len(), Equals, 1)
+
+	g.Delete(expr)
+	c.Assert(g.equivalents.Len(), Equals, 0)
+
+	g.Delete(expr)
+	c.Assert(g.equivalents.Len(), Equals, 0)
+}
+
+func (s *testCascadesSuite) TestGroupExists(c *C) {
+	p := &plannercore.LogicalLimit{}
+	expr := NewGroupExpr(p)
+	g := NewGroup(expr)
+	c.Assert(g.Exists(expr), IsTrue)
+
+	g.Delete(expr)
+	c.Assert(g.Exists(expr), IsFalse)
+}