perf(results): yielding row→string convert (no isolate double-copy) (#421)

lib/core/database/result_row_string_convert.dart

@@ -0,0 +1,33 @@
+/// Converts SQL result cells to display strings without a second isolate copy.
+///
+/// Prefer this over [compute] for large matrices: shipping `List<List<Object?>>`
+/// across isolates often costs more than `toString()` itself and roughly
+/// doubles peak memory. Yielding every [yieldEvery] rows keeps the UI isolate
+/// responsive for 10k+ row caps.
+library;
+
+const int kResultStringConvertYieldEvery = 250;
+
+/// Maps null cells to `'NULL'` and others via [Object.toString].
+String resultCellToDisplayString(Object? value) =>
+    value == null ? 'NULL' : value.toString();
+
+/// Converts [rowValues] to string rows, yielding periodically.
+Future<List<List<String>>> convertResultRowsToStringsYielding(
+  List<List<Object?>> rowValues, {
+  int yieldEvery = kResultStringConvertYieldEvery,
+}) async {
+  if (rowValues.isEmpty) return const [];
+
+  final out = <List<String>>[];
+  for (var i = 0; i < rowValues.length; i++) {
+    final row = rowValues[i];
+    out.add([
+      for (final value in row) resultCellToDisplayString(value),
+    ]);
+    if (yieldEvery > 0 && (i + 1) % yieldEvery == 0) {
+      await Future<void>.delayed(Duration.zero);
+    }
+  }
+  return out;
+}

lib/features/mysql/mysql_sql_workspace.dart

@@ -1,13 +1,13 @@
 import 'dart:async';
 import 'dart:io';
 
-import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart' as material;
 import 'package:flutter/services.dart' show LogicalKeyboardKey;
 import 'package:file_selector/file_selector.dart';
 import 'package:querya_desktop/core/actions/sql_editor_actions.dart';
 import 'package:querya_desktop/core/actions/sql_editor_command_bridge.dart';
 import 'package:querya_desktop/core/database/mysql_service.dart';
+import 'package:querya_desktop/core/database/result_row_string_convert.dart';
 import 'package:querya_desktop/core/layout/vertical_split_pane.dart';
 import 'package:querya_desktop/core/storage/app_settings.dart';
 import 'package:querya_desktop/core/storage/local_db.dart';
@@ -18,7 +18,6 @@ import 'package:querya_desktop/features/main_screen/query_editor_tab.dart';
 import 'package:querya_desktop/features/main_screen/results_tab.dart';
 import 'package:querya_desktop/features/main_screen/sql_editor_chrome.dart';
 import 'package:querya_desktop/features/main_screen/sql_query_history_dialog.dart';
-import 'package:querya_desktop/features/mysql/mysql_result_utils.dart';
 import 'package:querya_desktop/shared/widgets/widgets.dart';
 
 /// Ad-hoc SQL editor + results for MySQL / MariaDB.
@@ -192,7 +191,8 @@ class _MysqlSqlWorkspaceState extends material.State<MysqlSqlWorkspace> {
         cols.add(c.name.isNotEmpty ? c.name : 'col_${cols.length}');
       }
 
-      final rawRows = <List<Object?>>[];
+      // Convert while streaming — no Object? matrix + isolate double-copy (#421).
+      final outRows = <List<String>>[];
       var n = 0;
       final cap = _resultMaxRows;
       var truncated = false;
@@ -201,17 +201,18 @@ class _MysqlSqlWorkspaceState extends material.State<MysqlSqlWorkspace> {
           truncated = true;
           break;
         }
-        rawRows.add(
-          List.generate(row.numOfColumns, (i) => row.colAt(i)),
+        outRows.add(
+          List.generate(
+            row.numOfColumns,
+            (i) => resultCellToDisplayString(row.colAt(i)),
+          ),
         );
         n++;
+        if (n % kResultStringConvertYieldEvery == 0) {
+          await Future<void>.delayed(Duration.zero);
+        }
       }
 
-      final job = MysqlResultConvertJob(rowValues: rawRows);
-      final outRows = rawRows.length > 500
-          ? await compute(convertMysqlResultRowsToStrings, job)
-          : convertMysqlResultRowsToStrings(job);
-
       int? affected;
       if (cols.isEmpty && outRows.isEmpty) {
         affected = _affectedInt(rs.affectedRows);

lib/features/postgresql/postgres_sql_workspace.dart

@@ -1,16 +1,15 @@
 import 'dart:async';
 import 'dart:io';
 
-import 'package:flutter/foundation.dart' show compute;
 import 'package:flutter/material.dart' as material;
 import 'package:flutter/services.dart' show LogicalKeyboardKey;
 import 'package:file_selector/file_selector.dart';
-import 'package:querya_desktop/features/postgresql/postgres_result_utils.dart';
 import 'package:querya_desktop/core/actions/sql_editor_actions.dart';
 import 'package:querya_desktop/core/actions/sql_editor_command_bridge.dart';
 import 'package:postgres/postgres.dart' as pg;
 import 'package:querya_desktop/core/database/postgres_service.dart';
 import 'package:querya_desktop/core/database/postgres_sql.dart';
+import 'package:querya_desktop/core/database/result_row_string_convert.dart';
 import 'package:querya_desktop/core/layout/vertical_split_pane.dart';
 import 'package:querya_desktop/core/storage/app_settings.dart';
 import 'package:querya_desktop/core/storage/local_db.dart';
@@ -359,10 +358,8 @@ class _PostgresSqlWorkspaceState extends material.State<PostgresSqlWorkspace> {
         n++;
       }
 
-      final job = PostgresResultConvertJob(rowValues: rawRows);
-      final outRows = rawRows.length > 500
-          ? await compute(convertPostgresResultRowsToStrings, job)
-          : convertPostgresResultRowsToStrings(job);
+      // Yielding convert avoids isolate double-copy of the matrix (#421).
+      final outRows = await convertResultRowsToStringsYielding(rawRows);
 
       setState(() {
         _columns = cols;

lib/features/postgresql/postgres_table_view.dart

@@ -1,7 +1,7 @@
-import 'package:flutter/foundation.dart' show compute;
 import 'package:flutter/material.dart' as material;
 import 'package:querya_desktop/core/database/postgres_connection.dart';
 import 'package:querya_desktop/core/database/postgres_service.dart';
+import 'package:querya_desktop/core/database/result_row_string_convert.dart';
 import 'package:querya_desktop/core/storage/local_db.dart';
 import 'package:querya_desktop/features/postgresql/postgres_sql_editor_dialog.dart';
 import 'package:querya_desktop/features/postgresql/postgres_table_privileges_dialog.dart';
@@ -187,11 +187,12 @@ class _PostgresTableViewState extends material.State<PostgresTableView> {
         (i) => result.schema.columns[i].columnName ?? 'col_$i',
       );
 
-      final rawRows = result.map((row) {
-        return List<dynamic>.generate(row.length, (i) => row[i]);
-      }).toList();
+      final rawRows = <List<Object?>>[
+        for (final row in result)
+          List<Object?>.generate(row.length, (i) => row[i]),
+      ];
 
-      final stringRows = await compute(convertResultRowsToStrings, rawRows);
+      final stringRows = await convertResultRowsToStringsYielding(rawRows);
 
       if (!mounted) return;
       setState(() {
@@ -235,11 +236,12 @@ class _PostgresTableViewState extends material.State<PostgresTableView> {
         (i) => result.schema.columns[i].columnName ?? 'col_$i',
       );
 
-      final rawRows = result.map((row) {
-        return List<dynamic>.generate(row.length, (i) => row[i]);
-      }).toList();
+      final rawRows = <List<Object?>>[
+        for (final row in result)
+          List<Object?>.generate(row.length, (i) => row[i]),
+      ];
 
-      final stringRows = await compute(convertResultRowsToStrings, rawRows);
+      final stringRows = await convertResultRowsToStringsYielding(rawRows);
 
       if (!mounted) return;
       setState(() {

lib/features/sqlite/sqlite_sql_workspace.dart

@@ -1,14 +1,13 @@
 import 'dart:async';
 import 'dart:io';
-import 'package:flutter/foundation.dart' show compute;
 import 'package:flutter/material.dart' as material;
 import 'package:flutter/services.dart' show LogicalKeyboardKey;
 import 'package:file_selector/file_selector.dart';
-import 'package:querya_desktop/features/sqlite/sqlite_result_utils.dart';
 import 'package:querya_desktop/core/actions/sql_editor_actions.dart';
 import 'package:querya_desktop/core/actions/sql_editor_command_bridge.dart';
-import 'package:querya_desktop/core/database/sql_limit.dart';
+import 'package:querya_desktop/core/database/result_row_string_convert.dart';
 import 'package:querya_desktop/core/database/sqlite_service.dart';
+import 'package:querya_desktop/core/database/sql_limit.dart';
 import 'package:querya_desktop/core/layout/vertical_split_pane.dart';
 import 'package:querya_desktop/core/storage/app_settings.dart';
 import 'package:querya_desktop/core/storage/local_db.dart';
@@ -178,10 +177,8 @@ class _SqliteSqlWorkspaceState extends material.State<SqliteSqlWorkspace> {
         return cols.map((col) => row[col]).toList();
       }).toList();
 
-      final job = SqliteResultConvertJob(rowValues: rawRows);
-      final outRows = rawRows.length > 500
-          ? await compute(convertSqliteResultRowsToStrings, job)
-          : convertSqliteResultRowsToStrings(job);
+      // Yielding convert avoids isolate double-copy of the matrix (#421).
+      final outRows = await convertResultRowsToStringsYielding(rawRows);
 
       setState(() {
         _columns = cols;

test/core/database/result_row_string_convert_test.dart

@@ -0,0 +1,25 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:querya_desktop/core/database/result_row_string_convert.dart';
+
+void main() {
+  group('convertResultRowsToStringsYielding', () {
+    test('maps null to NULL and yields without isolate', () async {
+      final rows = <List<Object?>>[
+        [1, null, 'a'],
+        [2, 'x', null],
+      ];
+      final out = await convertResultRowsToStringsYielding(
+        rows,
+        yieldEvery: 1,
+      );
+      expect(out, [
+        ['1', 'NULL', 'a'],
+        ['2', 'x', 'NULL'],
+      ]);
+    });
+
+    test('empty input returns empty', () async {
+      expect(await convertResultRowsToStringsYielding(const []), isEmpty);
+    });
+  });
+}