should be it

external/duckdb/test/api/test_custom_allocator.cpp

@@ -0,0 +1,56 @@
+#include "catch.hpp"
+#include "test_helpers.hpp"
+#include "duckdb/main/appender.hpp"
+#include "duckdb/common/atomic.hpp"
+
+using namespace duckdb;
+using namespace std;
+
+struct MyAllocateData : public PrivateAllocatorData {
+	MyAllocateData(atomic<idx_t> *memory_counter_p) : memory_counter(memory_counter_p) {
+	}
+
+	atomic<idx_t> *memory_counter;
+};
+
+data_ptr_t my_allocate_function(PrivateAllocatorData *private_data, idx_t size) {
+	auto my_allocate_data = (MyAllocateData *)private_data;
+	*my_allocate_data->memory_counter += size;
+	return data_ptr_cast(malloc(size));
+}
+
+void my_free_function(PrivateAllocatorData *private_data, data_ptr_t pointer, idx_t size) {
+	auto my_allocate_data = (MyAllocateData *)private_data;
+	*my_allocate_data->memory_counter -= size;
+	free(pointer);
+}
+
+data_ptr_t my_reallocate_function(PrivateAllocatorData *private_data, data_ptr_t pointer, idx_t old_size, idx_t size) {
+	auto my_allocate_data = (MyAllocateData *)private_data;
+	*my_allocate_data->memory_counter -= old_size;
+	*my_allocate_data->memory_counter += size;
+	return data_ptr_cast(realloc(pointer, size));
+}
+
+TEST_CASE("Test using a custom allocator", "[api][.]") {
+	atomic<idx_t> memory_counter;
+	memory_counter = 0;
+
+	REQUIRE(memory_counter.load() == 0);
+
+	DBConfig config;
+	config.allocator = make_uniq<Allocator>(my_allocate_function, my_free_function, my_reallocate_function,
+	                                        make_uniq<MyAllocateData>(&memory_counter));
+	DuckDB db(nullptr, &config);
+	Connection con(db);
+	REQUIRE_NO_FAIL(con.Query("CREATE TABLE tbl AS SELECT * FROM range(1000000)"));
+
+	// check that the memory counter reported anything
+	REQUIRE(memory_counter.load() > 0);
+	auto table_memory_usage = memory_counter.load();
+
+	REQUIRE_NO_FAIL(con.Query("DROP TABLE tbl"));
+
+	// check that the memory counter usage has decreased after we dropped the table
+	REQUIRE(memory_counter.load() < table_memory_usage);
+}