Merge pull request #157 from poyrazK/perf/group-by-optimization

perf: DirectIndexAgg for low-cardinality integer GROUP BY

Author: poyrazK

benchmarks/duckdb_comparison_bench.cpp

@@ -54,6 +54,7 @@ struct CloudSQLContext {
         txn_manager = std::make_unique<transaction::TransactionManager>(*lock_manager, *catalog, *bpm);
         executor = std::make_unique<QueryExecutor>(*catalog, *bpm, *lock_manager, *txn_manager);
         executor->set_local_only(true);
+        executor->set_storage_manager(storage.get());  // Enable use_vectorized for large scans
 
         // Create lineitem table (TPC-H schema, simplified)
         CreateTableStatement create_stmt;

include/executor/types.hpp

@@ -243,6 +243,13 @@ class ColumnVector {
         size_ = 0;
         null_bitmap_.clear();
     }
+
+    /**
+     * @brief Steals data from another column vector by swapping internal buffers.
+     * After steal(), 'other' is emptied and 'this' holds the original data from 'other'.
+     * Throws std::runtime_error if types are incompatible.
+     */
+    virtual void steal(ColumnVector&& other) = 0;
 };
 
 /**
@@ -328,6 +335,14 @@ class NumericVector : public ColumnVector {
         ColumnVector::clear();
         data_.clear();
     }
+
+    void steal(ColumnVector&& other) override {
+        auto* other_num = dynamic_cast<NumericVector<T>*>(&other);
+        if (!other_num) throw std::runtime_error("NumericVector::steal: type mismatch");
+        data_.swap(other_num->data_);
+        null_bitmap_.swap(other_num->null_bitmap_);
+        std::swap(size_, other_num->size_);
+    }
 };
 
 /**
@@ -392,6 +407,14 @@ class StringVector : public ColumnVector {
         ColumnVector::clear();
         data_.clear();
     }
+
+    void steal(ColumnVector&& other) override {
+        auto* other_str = dynamic_cast<StringVector*>(&other);
+        if (!other_str) throw std::runtime_error("StringVector::steal: type mismatch");
+        data_.swap(other_str->data_);
+        null_bitmap_.swap(other_str->null_bitmap_);
+        std::swap(size_, other_str->size_);
+    }
 };
 
 /**