Implement CountRelTableOptimizer

src/include/optimizer/count_rel_table_optimizer.h

@@ -0,0 +1,49 @@
+#pragma once
+
+#include "logical_operator_visitor.h"
+#include "planner/operator/logical_plan.h"
+
+namespace lbug {
+namespace main {
+class ClientContext;
+}
+
+namespace optimizer {
+
+/**
+ * This optimizer detects patterns where we're counting all rows from a single rel table
+ * without any filters, and replaces the scan + aggregate with a direct count from table metadata.
+ *
+ * Pattern detected:
+ *   AGGREGATE (COUNT_STAR only, no keys) →
+ *   PROJECTION (empty or pass-through) →
+ *   EXTEND (single rel table) →
+ *   SCAN_NODE_TABLE
+ *
+ * This pattern is replaced with:
+ *   COUNT_REL_TABLE (new operator that directly reads the count from table metadata)
+ */
+class CountRelTableOptimizer : public LogicalOperatorVisitor {
+public:
+    explicit CountRelTableOptimizer(main::ClientContext* context) : context{context} {}
+
+    void rewrite(planner::LogicalPlan* plan);
+
+private:
+    std::shared_ptr<planner::LogicalOperator> visitOperator(
+        const std::shared_ptr<planner::LogicalOperator>& op);
+
+    std::shared_ptr<planner::LogicalOperator> visitAggregateReplace(
+        std::shared_ptr<planner::LogicalOperator> op) override;
+
+    // Check if the aggregate is a simple COUNT(*) with no keys
+    bool isSimpleCountStar(planner::LogicalOperator* op) const;
+
+    // Check if the plan below aggregate matches the pattern for optimization
+    bool canOptimize(planner::LogicalOperator* aggregate) const;
+
+    main::ClientContext* context;
+};
+
+} // namespace optimizer
+} // namespace lbug

src/include/optimizer/logical_operator_visitor.h

@@ -39,6 +39,12 @@ class LogicalOperatorVisitor {
         return op;
     }
 
+    virtual void visitCountRelTable(planner::LogicalOperator* /*op*/) {}
+    virtual std::shared_ptr<planner::LogicalOperator> visitCountRelTableReplace(
+        std::shared_ptr<planner::LogicalOperator> op) {
+        return op;
+    }
+
     virtual void visitDelete(planner::LogicalOperator* /*op*/) {}
     virtual std::shared_ptr<planner::LogicalOperator> visitDeleteReplace(
         std::shared_ptr<planner::LogicalOperator> op) {

src/include/planner/operator/logical_operator.h

@@ -17,6 +17,7 @@ enum class LogicalOperatorType : uint8_t {
     ATTACH_DATABASE,
     COPY_FROM,
     COPY_TO,
+    COUNT_REL_TABLE,
     CREATE_MACRO,
     CREATE_SEQUENCE,
     CREATE_TABLE,

src/include/planner/operator/scan/logical_count_rel_table.h

@@ -0,0 +1,84 @@
+#pragma once
+
+#include "binder/expression/expression.h"
+#include "binder/expression/node_expression.h"
+#include "catalog/catalog_entry/rel_group_catalog_entry.h"
+#include "common/enums/extend_direction.h"
+#include "planner/operator/logical_operator.h"
+
+namespace lbug {
+namespace planner {
+
+struct LogicalCountRelTablePrintInfo final : OPPrintInfo {
+    std::string relTableName;
+    std::shared_ptr<binder::Expression> countExpr;
+
+    LogicalCountRelTablePrintInfo(std::string relTableName,
+        std::shared_ptr<binder::Expression> countExpr)
+        : relTableName{std::move(relTableName)}, countExpr{std::move(countExpr)} {}
+
+    std::string toString() const override {
+        return "Table: " + relTableName + ", Count: " + countExpr->toString();
+    }
+
+    std::unique_ptr<OPPrintInfo> copy() const override {
+        return std::make_unique<LogicalCountRelTablePrintInfo>(relTableName, countExpr);
+    }
+};
+
+/**
+ * LogicalCountRelTable is an optimized operator that counts the number of rows
+ * in a rel table by scanning through bound nodes and counting edges.
+ *
+ * This operator is created by CountRelTableOptimizer when it detects:
+ *   COUNT(*) over a single rel table with no filters
+ */
+class LogicalCountRelTable final : public LogicalOperator {
+    static constexpr LogicalOperatorType type_ = LogicalOperatorType::COUNT_REL_TABLE;
+
+public:
+    LogicalCountRelTable(catalog::RelGroupCatalogEntry* relGroupEntry,
+        std::vector<common::table_id_t> relTableIDs,
+        std::vector<common::table_id_t> boundNodeTableIDs,
+        std::shared_ptr<binder::NodeExpression> boundNode, common::ExtendDirection direction,
+        std::shared_ptr<binder::Expression> countExpr)
+        : LogicalOperator{type_}, relGroupEntry{relGroupEntry}, relTableIDs{std::move(relTableIDs)},
+          boundNodeTableIDs{std::move(boundNodeTableIDs)}, boundNode{std::move(boundNode)},
+          direction{direction}, countExpr{std::move(countExpr)} {
+        cardinality = 1; // Always returns exactly one row
+    }
+
+    void computeFactorizedSchema() override;
+    void computeFlatSchema() override;
+
+    std::string getExpressionsForPrinting() const override { return countExpr->toString(); }
+
+    catalog::RelGroupCatalogEntry* getRelGroupEntry() const { return relGroupEntry; }
+    const std::vector<common::table_id_t>& getRelTableIDs() const { return relTableIDs; }
+    const std::vector<common::table_id_t>& getBoundNodeTableIDs() const {
+        return boundNodeTableIDs;
+    }
+    std::shared_ptr<binder::NodeExpression> getBoundNode() const { return boundNode; }
+    common::ExtendDirection getDirection() const { return direction; }
+    std::shared_ptr<binder::Expression> getCountExpr() const { return countExpr; }
+
+    std::unique_ptr<OPPrintInfo> getPrintInfo() const override {
+        return std::make_unique<LogicalCountRelTablePrintInfo>(relGroupEntry->getName(), countExpr);
+    }
+
+    std::unique_ptr<LogicalOperator> copy() override {
+        return std::make_unique<LogicalCountRelTable>(relGroupEntry, relTableIDs, boundNodeTableIDs,
+            boundNode, direction, countExpr);
+    }
+
+private:
+    catalog::RelGroupCatalogEntry* relGroupEntry;
+    std::vector<common::table_id_t> relTableIDs;
+    std::vector<common::table_id_t> boundNodeTableIDs;
+    std::shared_ptr<binder::NodeExpression> boundNode;
+    common::ExtendDirection direction;
+    std::shared_ptr<binder::Expression> countExpr;
+};
+
+} // namespace planner
+} // namespace lbug

src/include/processor/operator/physical_operator.h

@@ -22,6 +22,7 @@ enum class PhysicalOperatorType : uint8_t {
     ATTACH_DATABASE,
     BATCH_INSERT,
     COPY_TO,
+    COUNT_REL_TABLE,
     CREATE_MACRO,
     CREATE_SEQUENCE,
     CREATE_TABLE,

src/include/processor/operator/scan/count_rel_table.h

@@ -0,0 +1,62 @@
+#pragma once
+
+#include "common/enums/rel_direction.h"
+#include "processor/operator/physical_operator.h"
+#include "storage/table/node_table.h"
+#include "storage/table/rel_table.h"
+
+namespace lbug {
+namespace processor {
+
+struct CountRelTablePrintInfo final : OPPrintInfo {
+    std::string relTableName;
+
+    explicit CountRelTablePrintInfo(std::string relTableName)
+        : relTableName{std::move(relTableName)} {}
+
+    std::string toString() const override { return "Table: " + relTableName; }
+
+    std::unique_ptr<OPPrintInfo> copy() const override {
+        return std::make_unique<CountRelTablePrintInfo>(relTableName);
+    }
+};
+
+/**
+ * CountRelTable is a source operator that counts edges in a rel table
+ * by scanning through all bound nodes and counting their edges.
+ * It creates its own internal vectors for node scanning (not exposed in ResultSet).
+ */
+class CountRelTable final : public PhysicalOperator {
+    static constexpr PhysicalOperatorType type_ = PhysicalOperatorType::COUNT_REL_TABLE;
+
+public:
+    CountRelTable(std::vector<storage::NodeTable*> nodeTables,
+        std::vector<storage::RelTable*> relTables, common::RelDataDirection direction,
+        DataPos countOutputPos, physical_op_id id, std::unique_ptr<OPPrintInfo> printInfo)
+        : PhysicalOperator{type_, id, std::move(printInfo)}, nodeTables{std::move(nodeTables)},
+          relTables{std::move(relTables)}, direction{direction}, countOutputPos{countOutputPos} {}
+
+    bool isSource() const override { return true; }
+    bool isParallel() const override { return false; }
+
+    void initLocalStateInternal(ResultSet* resultSet, ExecutionContext* context) override;
+
+    bool getNextTuplesInternal(ExecutionContext* context) override;
+
+    std::unique_ptr<PhysicalOperator> copy() override {
+        return std::make_unique<CountRelTable>(nodeTables, relTables, direction, countOutputPos, id,
+            printInfo->copy());
+    }
+
+private:
+    std::vector<storage::NodeTable*> nodeTables;
+    std::vector<storage::RelTable*> relTables;
+    common::RelDataDirection direction;
+    DataPos countOutputPos;
+    common::ValueVector* countVector;
+    bool hasExecuted;
+    common::row_idx_t totalCount;
+};
+
+} // namespace processor
+} // namespace lbug

src/include/processor/plan_mapper.h

@@ -90,6 +90,8 @@ class PlanMapper {
     std::unique_ptr<PhysicalOperator> mapCopyRelFrom(
         const planner::LogicalOperator* logicalOperator);
     std::unique_ptr<PhysicalOperator> mapCopyTo(const planner::LogicalOperator* logicalOperator);
+    std::unique_ptr<PhysicalOperator> mapCountRelTable(
+        const planner::LogicalOperator* logicalOperator);
     std::unique_ptr<PhysicalOperator> mapCreateMacro(
         const planner::LogicalOperator* logicalOperator);
     std::unique_ptr<PhysicalOperator> mapCreateSequence(

src/optimizer/CMakeLists.txt

@@ -4,6 +4,7 @@ add_library(lbug_optimizer
         agg_key_dependency_optimizer.cpp
         cardinality_updater.cpp
         correlated_subquery_unnest_solver.cpp
+        count_rel_table_optimizer.cpp
         factorization_rewriter.cpp
         filter_push_down_optimizer.cpp
         logical_operator_collector.cpp