Eliminte the useless row collect.

src/graph/optimizer/CMakeLists.txt

@@ -45,6 +45,7 @@ nebula_add_library(
     rule/PushLimitDownEdgeIndexPrefixScanRule.cpp
     rule/PushLimitDownEdgeIndexRangeScanRule.cpp
     rule/PushLimitDownProjectRule.cpp
+    rule/EliminateRowCollectRule.cpp
 )
 
 nebula_add_subdirectory(test)

src/graph/optimizer/rule/EliminateRowCollectRule.cpp

@@ -0,0 +1,69 @@
+/* Copyright (c) 2021 vesoft inc. All rights reserved.
+ *
+ * This source code is licensed under Apache 2.0 License.
+ */
+
+#include "graph/optimizer/rule/EliminateRowCollectRule.h"
+
+#include "graph/optimizer/OptContext.h"
+#include "graph/optimizer/OptGroup.h"
+#include "graph/planner/plan/PlanNode.h"
+#include "graph/planner/plan/Query.h"
+
+using nebula::graph::DataCollect;
+using nebula::graph::PlanNode;
+using nebula::graph::Project;
+using nebula::graph::QueryContext;
+
+namespace nebula {
+namespace opt {
+
+std::unique_ptr<OptRule> EliminateRowCollectRule::kInstance =
+    std::unique_ptr<EliminateRowCollectRule>(new EliminateRowCollectRule());
+
+EliminateRowCollectRule::EliminateRowCollectRule() { RuleSet::QueryRules().addRule(this); }
+
+// TODO match DataCollect->(Any Node with real result)
+const Pattern& EliminateRowCollectRule::pattern() const {
+  static Pattern pattern = Pattern::create(graph::PlanNode::Kind::kDataCollect,
+                                           {Pattern::create(graph::PlanNode::Kind::kProject)});
+  return pattern;
+}
+
+bool EliminateRowCollectRule::match(OptContext* octx, const MatchedResult& matched) const {
+  if (!OptRule::match(octx, matched)) {
+    return false;
+  }
+  const auto* collectNode = static_cast<const DataCollect*>(matched.node->node());
+  if (collectNode->kind() != DataCollect::DCKind::kRowBasedMove) {
+    return false;
+  }
+  return true;
+}
+
+StatusOr<OptRule::TransformResult> EliminateRowCollectRule::transform(
+    OptContext* octx, const MatchedResult& matched) const {
+  auto dataCollectGroupNode = matched.node;
+  auto projGroupNode = matched.dependencies.front().node;
+
+  const auto dataCollect = static_cast<const DataCollect*>(dataCollectGroupNode->node());
+  const auto proj = static_cast<const Project*>(projGroupNode->node());
+
+  auto newProj = static_cast<Project*>(proj->clone());
+  newProj->setOutputVar(dataCollect->outputVar());
+  auto newProjGroupNode = OptGroupNode::create(octx, newProj, dataCollectGroupNode->group());
+
+  for (auto dep : projGroupNode->dependencies()) {
+    newProjGroupNode->dependsOn(dep);
+  }
+
+  TransformResult result;
+  result.eraseAll = true;
+  result.newGroupNodes.emplace_back(newProjGroupNode);
+  return result;
+}
+
+std::string EliminateRowCollectRule::toString() const { return "EliminateRowCollectRule"; }
+
+}  // namespace opt
+}  // namespace nebula

src/graph/optimizer/rule/EliminateRowCollectRule.h

@@ -0,0 +1,30 @@
+/* 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 opt {
+
+class EliminateRowCollectRule 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:
+  EliminateRowCollectRule();
+
+  static std::unique_ptr<OptRule> kInstance;
+};
+
+}  // namespace opt
+}  // namespace nebula

tests/tck/features/optimizer/PushLimitDownGetNeighborsRule.feature

@@ -18,7 +18,6 @@ Feature: Push Limit down rule
       | "Luka Doncic"     |
     And the execution plan should be:
       | id | name         | dependencies | operator info  |
-      | 4  | DataCollect  | 5            |                |
       | 5  | Project      | 6            |                |
       | 6  | Limit        | 7            |                |
       | 7  | GetNeighbors | 0            | {"limit": "2"} |
@@ -39,7 +38,6 @@ Feature: Push Limit down rule
       | 1998       |
     And the execution plan should be:
       | id | name         | dependencies | operator info  |
-      | 0  | DataCollect  | 1            |                |
       | 1  | Project      | 2            |                |
       | 2  | Limit        | 3            |                |
       | 3  | GetNeighbors | 4            | {"limit": "7"} |

tests/tck/features/optimizer/PushLimitDownProjectRule.feature

@@ -23,7 +23,6 @@ Feature: Push Limit down project rule
       | <("Tim Duncan" :bachelor{name: "Tim Duncan", speciality: "psychology"} :player{age: 42, name: "Tim Duncan"})-[:like@0 {likeness: 95}]->("Tony Parker" :player{age: 36, name: "Tony Parker"})>                                     |
     And the execution plan should be:
       | id | name           | dependencies | operator info |
-      | 9  | DataCollect    | 19           |               |
       | 19 | Project        | 16           |               |
       | 16 | Limit          | 11           |               |
       | 11 | Filter         | 4            |               |