[Enhancement]: support associative rule in join order (#11587)

Approved by: @aunjgr

pkg/sql/plan/associative_law.go

@@ -0,0 +1,55 @@
+// Copyright 2022 Matrix Origin
+//
+// 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 plan
+
+import "github.com/matrixorigin/matrixone/pkg/pb/plan"
+
+// for A*(B*C), if C.sel>0.9 and B<C, change this to (A*B)*C
+func (builder *QueryBuilder) applyAssociativeLaw(nodeID int32) int32 {
+	node := builder.qry.Nodes[nodeID]
+	if len(node.Children) > 0 {
+		for i, child := range node.Children {
+			node.Children[i] = builder.applyAssociativeLaw(child)
+		}
+	}
+	if node.NodeType != plan.Node_JOIN || node.JoinType != plan.Node_INNER {
+		return nodeID
+	}
+
+	rightChild := builder.qry.Nodes[node.Children[1]]
+	if rightChild.NodeType != plan.Node_JOIN || rightChild.JoinType != plan.Node_INNER {
+		return nodeID
+	}
+	NodeB := builder.qry.Nodes[rightChild.Children[0]]
+	NodeC := builder.qry.Nodes[rightChild.Children[1]]
+
+	if NodeC.Stats.Selectivity < 0.9 || NodeB.Stats.Outcnt >= NodeC.Stats.Outcnt {
+		return nodeID
+	}
+
+	node.Children[1] = NodeB.NodeId
+
+	determineHashOnPK(node.NodeId, builder)
+	if !node.Stats.HashmapStats.HashOnPK {
+		// a join b must be hash on primary key, or we can not do this change
+		node.Children[1] = rightChild.NodeId
+		return node.NodeId
+	}
+
+	rightChild.Children[0] = node.NodeId
+	ReCalcNodeStats(rightChild.NodeId, builder, true, false)
+	return rightChild.NodeId
+
+}

pkg/sql/plan/query_builder.go

@@ -1235,6 +1235,7 @@ func (builder *QueryBuilder) createQuery() (*Query, error) {
 		rootID = builder.determineJoinOrder(rootID)
 		rootID = builder.removeRedundantJoinCond(rootID)
 		ReCalcNodeStats(rootID, builder, true, false)
+		rootID = builder.applyAssociativeLaw(rootID)
 		builder.applySwapRuleByStats(rootID, true)
 		rootID = builder.aggPullup(rootID, rootID)
 		ReCalcNodeStats(rootID, builder, true, false)