Stop scan edge opt when build path (vesoft-inc#944)

* Stop scanV -> scanE optRule when buildPath

delete: av->traverse->scanV
add: project-> limit -> av->traverse->sv
add: project-> av ->traverse->sv

exclude optRule for buildPath in project.colums()

Comments added

lint: clang-format

[WIP] Fixing regression when return e, e.foo.bar

The limit info is lost in this case

Fix after vesoft-inc#4146

OptGroup was refactored in vesoft-inc#4146

Removed GetEdgesTransformRule

* Rebase on vesoft-inc#4277 Remove useless AppendVertices

As this rule only aplied for
   match ()-[e]->() return e limit 1
when 1. there is no index on e and 2. limit cluase
exists, thus we could assert that AppendVertices
will be removed by EliminateAppendVerticesRule

//  Tranformation:
//  Before:
// +---------+---------+
// |      Project      |
// +---------+---------+
//           |
// +---------+---------+
// |       Limit       |
// +---------+---------+
//           |
// +---------+---------+
// |      Traverse     |
// +---------+---------+
//           |
// +---------+---------+
// |    ScanVertices   |
// +---------+---------+
//
//  After:
// +---------+---------+
// |      Project      |
// +---------+---------+
//           |
// +---------+---------+
// |       Limit       |
// +---------+---------+
//           |
// +---------+---------+
// |      Project      |
// +---------+---------+
//           |
// +---------+---------+
// |      ScanEdges    |
// +---------+---------+

* Addressing Shylock-Hg's comment

* Make linter happy

* Fix after EliminateAppendVerticesRule merged

and linting

* Reusing functions in GetEdgesTransformRule

* Addressing comment from Shylock-Hg & rebase

Co-authored-by: cpw <13495049+CPWstatic@users.noreply.github.com>

Co-authored-by: Wey Gu <weyl.gu@gmail.com>
Co-authored-by: cpw <13495049+CPWstatic@users.noreply.github.com>

src/graph/optimizer/CMakeLists.txt

@@ -45,6 +45,7 @@ nebula_add_library(
     rule/PushLimitDownProjectRule.cpp
     rule/EliminateRowCollectRule.cpp
     rule/PushLimitDownScanAppendVerticesRule.cpp
+    rule/GetEdgesTransformAppendVerticesLimitRule.cpp
     rule/GetEdgesTransformRule.cpp
     rule/PushLimitDownScanEdgesAppendVerticesRule.cpp
     rule/PushTopNDownIndexScanRule.cpp

src/graph/optimizer/rule/GetEdgesTransformAppendVerticesLimitRule.cpp

@@ -0,0 +1,148 @@
+/* Copyright (c) 2021 vesoft inc. All rights reserved.
+ *
+ * This source code is licensed under Apache 2.0 License.
+ */
+
+#include "graph/optimizer/rule/GetEdgesTransformAppendVerticesLimitRule.h"
+
+#include "common/expression/Expression.h"
+#include "graph/optimizer/OptContext.h"
+#include "graph/optimizer/OptGroup.h"
+#include "graph/optimizer/rule/GetEdgesTransformUtils.h"
+#include "graph/planner/plan/PlanNode.h"
+#include "graph/planner/plan/Query.h"
+#include "graph/visitor/ExtractFilterExprVisitor.h"
+
+using nebula::Expression;
+using nebula::graph::AppendVertices;
+using nebula::graph::Limit;
+using nebula::graph::PlanNode;
+using nebula::graph::Project;
+using nebula::graph::QueryContext;
+using nebula::graph::ScanEdges;
+using nebula::graph::ScanVertices;
+using nebula::graph::Traverse;
+
+namespace nebula {
+namespace opt {
+
+std::unique_ptr<OptRule> GetEdgesTransformAppendVerticesLimitRule::kInstance =
+    std::unique_ptr<GetEdgesTransformAppendVerticesLimitRule>(
+        new GetEdgesTransformAppendVerticesLimitRule());
+
+GetEdgesTransformAppendVerticesLimitRule::GetEdgesTransformAppendVerticesLimitRule() {
+  RuleSet::QueryRules().addRule(this);
+}
+
+const Pattern &GetEdgesTransformAppendVerticesLimitRule::pattern() const {
+  static Pattern pattern = Pattern::create(
+      PlanNode::Kind::kProject,
+      {Pattern::create(
+          PlanNode::Kind::kLimit,
+          {Pattern::create(PlanNode::Kind::kAppendVertices,
+                           {Pattern::create(PlanNode::Kind::kTraverse,
+                                            {Pattern::create(PlanNode::Kind::kScanVertices)})})})});
+  return pattern;
+}
+
+bool GetEdgesTransformAppendVerticesLimitRule::match(OptContext *ctx,
+                                                     const MatchedResult &matched) const {
+  if (!OptRule::match(ctx, matched)) {
+    return false;
+  }
+  auto traverse = static_cast<const Traverse *>(matched.planNode({0, 0, 0, 0}));
+  auto project = static_cast<const Project *>(matched.planNode({0}));
+  const auto &colNames = traverse->colNames();
+  auto colSize = colNames.size();
+  DCHECK_GE(colSize, 2);
+  if (colNames[colSize - 2][0] != '_') {  // src
+    return false;
+  }
+  if (traverse->stepRange() != nullptr) {
+    return false;
+  }
+  for (auto yieldColumn : project->columns()->columns()) {
+    // exclude p=()-[e]->() return p limit 10
+    if (yieldColumn->expr()->kind() == nebula::Expression::Kind::kPathBuild) {
+      return false;
+    }
+  }
+  return true;
+}
+
+StatusOr<OptRule::TransformResult> GetEdgesTransformAppendVerticesLimitRule::transform(
+    OptContext *ctx, const MatchedResult &matched) const {
+  auto projectGroupNode = matched.node;
+  auto project = static_cast<const Project *>(projectGroupNode->node());
+
+  auto newProject = project->clone();
+  auto newProjectGroupNode = OptGroupNode::create(ctx, newProject, projectGroupNode->group());
+  newProject->setOutputVar(project->outputVar());
+
+  auto limitGroupNode = matched.dependencies.front().node;
+  auto limit = static_cast<const Limit *>(limitGroupNode->node());
+
+  auto newLimit = limit->clone();
+  auto newLimitGroup = OptGroup::create(ctx);
+  auto newLimitGroupNode = newLimitGroup->makeGroupNode(newLimit);
+  newLimit->setOutputVar(limit->outputVar());
+  newProject->setInputVar(newLimit->outputVar());
+
+  newProjectGroupNode->dependsOn(newLimitGroup);
+
+  auto appendVerticesGroupNode = matched.dependencies.front().dependencies.front().node;
+  auto appendVertices = static_cast<const AppendVertices *>(appendVerticesGroupNode->node());
+  auto traverseGroupNode =
+      matched.dependencies.front().dependencies.front().dependencies.front().node;
+  auto traverse = static_cast<const Traverse *>(traverseGroupNode->node());
+  auto scanVerticesGroupNode = matched.dependencies.front()
+                                   .dependencies.front()
+                                   .dependencies.front()
+                                   .dependencies.front()
+                                   .node;
+  auto qctx = ctx->qctx();
+
+  auto newAppendVertices = appendVertices->clone();
+  auto newAppendVerticesGroup = OptGroup::create(ctx);
+  auto colSize = appendVertices->colNames().size();
+  newAppendVertices->setOutputVar(appendVertices->outputVar());
+  newLimit->setInputVar(newAppendVertices->outputVar());
+  newAppendVertices->setColNames(
+      {appendVertices->colNames()[colSize - 2], appendVertices->colNames()[colSize - 1]});
+  auto newAppendVerticesGroupNode = newAppendVerticesGroup->makeGroupNode(newAppendVertices);
+
+  newLimitGroupNode->dependsOn(newAppendVerticesGroup);
+
+  auto *newScanEdges = GetEdgesTransformUtils::traverseToScanEdges(traverse, limit->count(qctx));
+  if (newScanEdges == nullptr) {
+    return TransformResult::noTransform();
+  }
+  auto newScanEdgesGroup = OptGroup::create(ctx);
+  auto newScanEdgesGroupNode = newScanEdgesGroup->makeGroupNode(newScanEdges);
+
+  auto *newProj =
+      GetEdgesTransformUtils::projectEdges(qctx, newScanEdges, traverse->colNames().back());
+  newProj->setInputVar(newScanEdges->outputVar());
+  newProj->setOutputVar(newAppendVertices->inputVar());
+  newProj->setColNames({traverse->colNames().back()});
+  auto newProjGroup = OptGroup::create(ctx);
+  auto newProjGroupNode = newProjGroup->makeGroupNode(newProj);
+
+  newAppendVerticesGroupNode->dependsOn(newProjGroup);
+  newProjGroupNode->dependsOn(newScanEdgesGroup);
+  for (auto dep : scanVerticesGroupNode->dependencies()) {
+    newScanEdgesGroupNode->dependsOn(dep);
+  }
+
+  TransformResult result;
+  result.eraseCurr = true;
+  result.newGroupNodes.emplace_back(newProjectGroupNode);
+  return result;
+}
+
+std::string GetEdgesTransformAppendVerticesLimitRule::toString() const {
+  return "GetEdgesTransformAppendVerticesLimitRule";
+}
+
+}  // namespace opt
+}  // namespace nebula

src/graph/optimizer/rule/GetEdgesTransformAppendVerticesLimitRule.h

@@ -0,0 +1,92 @@
+/* Copyright (c) 2021 vesoft inc. All rights reserved.
+ *
+ * This source code is licensed under Apache 2.0 License.
+ */
+
+#pragma once
+
+#include "graph/optimizer/OptRule.h"
+
+namespace nebula {
+
+namespace graph {
+class ScanEdges;
+class Project;
+class Traverse;
+class PlanNode;
+}  // namespace graph
+
+namespace opt {
+
+//  Convert [[ScanVertices]] to [[ScanEdges]] in certain cases
+//  Required conditions:
+//   1. Match the pattern
+//  Benefits:
+//   1. Avoid doing Traverse to optimize performance
+//  Query example:
+//   1. match ()-[e]->() return e limit 1
+//
+//  Tranformation:
+//  Before:
+// +---------+---------+
+// |      Project      |
+// +---------+---------+
+//           |
+// +---------+---------+
+// |       Limit       |
+// +---------+---------+
+//           |
+// +---------+---------+
+// |   AppendVertices  |
+// +---------+---------+
+//           |
+// +---------+---------+
+// |      Traverse     |
+// +---------+---------+
+//           |
+// +---------+---------+
+// |    ScanVertices   |
+// +---------+---------+
+//
+//  After:
+// +---------+---------+
+// |      Project      |
+// +---------+---------+
+//           |
+// +---------+---------+
+// |       Limit       |
+// +---------+---------+
+//           |
+// +---------+---------+
+// |   AppendVertices  |
+// +---------+---------+
+//           |
+// +---------+---------+
+// |      Project      |
+// +---------+---------+
+//           |
+// +---------+---------+
+// |      ScanEdges    |
+// +---------+---------+
+
+class GetEdgesTransformAppendVerticesLimitRule final : public OptRule {
+ public:
+  const Pattern &pattern() const override;
+
+  bool match(OptContext *ctx, const MatchedResult &matched) const override;
+  StatusOr<TransformResult> transform(OptContext *ctx, const MatchedResult &matched) const override;
+
+  std::string toString() const override;
+
+ private:
+  GetEdgesTransformAppendVerticesLimitRule();
+
+  static graph::Project *projectEdges(graph::QueryContext *qctx,
+                                      graph::PlanNode *input,
+                                      const std::string &colName);
+
+  static std::unique_ptr<OptRule> kInstance;
+};
+
+}  // namespace opt
+}  // namespace nebula