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support join reorder. (pingcap#1522)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,206 @@ | ||
| // Copyright 2016 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 plan | ||
|
|
||
| import ( | ||
| "sort" | ||
|
|
||
| "github.com/ngaut/log" | ||
| "github.com/pingcap/tidb/ast" | ||
| "github.com/pingcap/tidb/expression" | ||
| ) | ||
|
|
||
| // tryToGetJoinGroup tries to fetch a whole join group, which all joins is cartesian join. | ||
| func tryToGetJoinGroup(j *Join) ([]LogicalPlan, bool) { | ||
| if j.reordered || !j.cartesianJoin { | ||
| return nil, false | ||
| } | ||
| lChild := j.GetChildByIndex(0).(LogicalPlan) | ||
| rChild := j.GetChildByIndex(1).(LogicalPlan) | ||
| if nj, ok := lChild.(*Join); ok { | ||
| plans, valid := tryToGetJoinGroup(nj) | ||
| return append(plans, rChild), valid | ||
| } | ||
| return []LogicalPlan{lChild, rChild}, true | ||
| } | ||
|
|
||
| func findColumnIndexByGroup(groups []LogicalPlan, col *expression.Column) int { | ||
| for i, plan := range groups { | ||
| idx := plan.GetSchema().GetIndex(col) | ||
| if idx != -1 { | ||
| return i | ||
| } | ||
| } | ||
| log.Errorf("Unknown columns %s, from id %s, position %d", col.ToString(), col.FromID, col.Position) | ||
| return -1 | ||
| } | ||
|
|
||
| type joinReOrderSolver struct { | ||
| graph []edgeList | ||
| group []LogicalPlan | ||
| visited []bool | ||
| resultJoin LogicalPlan | ||
| groupRank []*rankInfo | ||
| allocator *idAllocator | ||
| } | ||
|
|
||
| type edgeList []*rankInfo | ||
|
|
||
| func (l edgeList) Len() int { | ||
| return len(l) | ||
| } | ||
|
|
||
| func (l edgeList) Less(i, j int) bool { | ||
| return l[i].rate < l[j].rate | ||
| } | ||
|
|
||
| func (l edgeList) Swap(i, j int) { | ||
| l[i], l[j] = l[j], l[i] | ||
| } | ||
|
|
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| type rankInfo struct { | ||
| nodeID int | ||
| rate float64 | ||
| } | ||
|
|
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| func (e *joinReOrderSolver) Less(i, j int) bool { | ||
| return e.groupRank[i].rate < e.groupRank[j].rate | ||
| } | ||
|
|
||
| func (e *joinReOrderSolver) Swap(i, j int) { | ||
| e.groupRank[i], e.groupRank[j] = e.groupRank[j], e.groupRank[i] | ||
| } | ||
|
|
||
| func (e *joinReOrderSolver) Len() int { | ||
| return len(e.groupRank) | ||
| } | ||
|
|
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| // reorderJoin implements a simple join reorder algorithm. It will extract all the equal conditions and compose them to a graph. | ||
| // Then walk through the graph and pick the nodes connected by some edges to compose a join tree. | ||
| // We will pick the node with least result set as early as possible. | ||
| func (e *joinReOrderSolver) reorderJoin(group []LogicalPlan, conds []expression.Expression) { | ||
| e.graph = make([]edgeList, len(group)) | ||
| e.group = group | ||
| e.visited = make([]bool, len(group)) | ||
| e.resultJoin = nil | ||
| e.groupRank = make([]*rankInfo, len(group)) | ||
| for i := 0; i < len(e.groupRank); i++ { | ||
| e.groupRank[i] = &rankInfo{ | ||
| nodeID: i, | ||
| rate: 1.0, | ||
| } | ||
| } | ||
| for _, cond := range conds { | ||
| if f, ok := cond.(*expression.ScalarFunction); ok { | ||
| if f.FuncName.L == ast.EQ { | ||
| lCol, lok := f.Args[0].(*expression.Column) | ||
| rCol, rok := f.Args[1].(*expression.Column) | ||
| if lok && rok && !lCol.Correlated && !rCol.Correlated { | ||
| lID := findColumnIndexByGroup(group, lCol) | ||
| rID := findColumnIndexByGroup(group, rCol) | ||
| if lID != rID { | ||
| e.graph[lID] = append(e.graph[lID], &rankInfo{nodeID: rID}) | ||
| e.graph[rID] = append(e.graph[rID], &rankInfo{nodeID: lID}) | ||
| continue | ||
| } | ||
| } | ||
| } | ||
| id := -1 | ||
| rate := 1.0 | ||
| cols, _ := extractColumn(f, nil, nil) | ||
| for _, col := range cols { | ||
| idx := findColumnIndexByGroup(group, col) | ||
| if id == -1 { | ||
| switch f.FuncName.L { | ||
| case ast.EQ: | ||
| rate *= 0.1 | ||
| case ast.LT, ast.LE, ast.GE, ast.GT: | ||
| rate *= 0.3 | ||
| // TODO: Estimate it more precisely in future. | ||
| default: | ||
| rate *= 0.9 | ||
| } | ||
| id = idx | ||
| } else { | ||
| id = -1 | ||
| break | ||
| } | ||
| } | ||
| if id != -1 { | ||
| e.groupRank[id].rate *= rate | ||
| } | ||
| } | ||
| } | ||
| for _, node := range e.graph { | ||
| for _, edge := range node { | ||
| edge.rate = e.groupRank[edge.nodeID].rate | ||
| } | ||
| } | ||
| sort.Sort(e) | ||
| for _, edge := range e.graph { | ||
| sort.Sort(edge) | ||
| } | ||
| var cartesianJoinGroup []LogicalPlan | ||
| for j := 0; j < len(e.groupRank); j++ { | ||
| i := e.groupRank[j].nodeID | ||
| if !e.visited[i] { | ||
| e.resultJoin = e.group[i] | ||
| e.walkGraphAndComposeJoin(i) | ||
| cartesianJoinGroup = append(cartesianJoinGroup, e.resultJoin) | ||
| } | ||
| } | ||
| e.makeBushyJoin(cartesianJoinGroup) | ||
| } | ||
|
|
||
| // Make cartesian join as bushy tree. | ||
| func (e *joinReOrderSolver) makeBushyJoin(cartesianJoinGroup []LogicalPlan) { | ||
| for len(cartesianJoinGroup) > 1 { | ||
| resultJoinGroup := make([]LogicalPlan, 0, len(cartesianJoinGroup)) | ||
| for i := 0; i < len(cartesianJoinGroup); i += 2 { | ||
| if i+1 == len(cartesianJoinGroup) { | ||
| resultJoinGroup = append(resultJoinGroup, cartesianJoinGroup[i]) | ||
| break | ||
| } | ||
| resultJoinGroup = append(resultJoinGroup, e.newJoin(cartesianJoinGroup[i], cartesianJoinGroup[i+1])) | ||
| } | ||
| cartesianJoinGroup = resultJoinGroup | ||
| } | ||
| e.resultJoin = cartesianJoinGroup[0] | ||
| } | ||
|
|
||
| func (e *joinReOrderSolver) newJoin(lChild, rChild LogicalPlan) *Join { | ||
| join := &Join{ | ||
| JoinType: InnerJoin, | ||
| reordered: true, | ||
| baseLogicalPlan: newBaseLogicalPlan(Jn, e.allocator), | ||
| } | ||
| join.initID() | ||
| join.SetChildren(lChild, rChild) | ||
| join.SetSchema(append(lChild.GetSchema().DeepCopy(), rChild.GetSchema().DeepCopy()...)) | ||
| lChild.SetParents(join) | ||
| rChild.SetParents(join) | ||
| return join | ||
| } | ||
|
|
||
| // walkGraph implements a dfs algorithm. Each time it picks a edge with lowest rate, which has been sorted before. | ||
| func (e *joinReOrderSolver) walkGraphAndComposeJoin(u int) { | ||
| e.visited[u] = true | ||
| for _, edge := range e.graph[u] { | ||
| v := edge.nodeID | ||
| if !e.visited[v] { | ||
| e.resultJoin = e.newJoin(e.resultJoin, e.group[v]) | ||
| e.walkGraphAndComposeJoin(v) | ||
| } | ||
| } | ||
| } |
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