fix(postgres): browse on read-only; page with ORDER BY PK; do not block on COUNT(*)

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- **Postgres Table Browser paging (#788)** — Browse stays on `PgSessionMode.readOnly`. `SELECT` uses `ORDER BY` primary-key columns when a PK exists. Row totals come from `pg_class.reltuples` instead of a blocking `COUNT(*)` before first paint (stale estimates below the current page are ignored so Next still works). Save / REFRESH stay on `tableWrite`.
 - **Postgres timestamptz / bytea / jsonb / arrays (#789)** — Table Browser and SQL results encode cells as PG literals (ISO timestamps, `\x` hex for bytea, JSON text for jsonb, `{1,2,3}` for arrays) instead of `Object.toString`. Schema uses `udt_name` so `ARRAY` / `USER-DEFINED` round-trip through `formatLiteral`.
 - **Postgres host/port SSL (#790)** — Host/port Use SSL/TLS stays `sslmode=require` (encrypt, no CA check) unless a Root CA is set, then `verify-full`. A URI `sslmode=` value still wins. The form documents the MITM tradeoff and writes `sslmode=verify-full` when saving a Root CA.
 - **Postgres custom-SQL allowlist (#791)** — Table Browser SQL dialog classifies the first statement after comments instead of substring `contains('insert ')`. `SELECT inserted_at` is allowed; `SELECT 1; DELETE FROM t` is rejected. `WITH … INSERT` is a write; `TABLE` / `VALUES` / `(SELECT …)` stay allowed.

lib/core/database/postgres_connection.dart

@@ -54,6 +54,14 @@ SslMode postgresResolveSslMode({
   return SslMode.require;
 }
 
+/// `pg_class.reltuples` → row estimate. Negative / unanalyzed → `null`.
+int? postgresReltuplesEstimate(Object? value) {
+  if (value == null) return null;
+  final n = value is num ? value.toDouble() : double.tryParse(value.toString());
+  if (n == null || n < 0) return null;
+  return n.round();
+}
+
 /// PostgreSQL connection using the pure-Dart `postgres` package.
 class PostgresConnection {
   PostgresConnection({
@@ -490,6 +498,29 @@ class PostgresConnection {
     );
   }
 
+  /// Planner row estimate (`pg_class.reltuples`), not a blocking `COUNT(*)`.
+  /// Unanalyzed relations (`-1`) and missing catalog rows return `null`.
+  Future<int?> estimateTableRows({
+    String schema = 'public',
+    required String table,
+  }) async {
+    if (!isConnected || _conn == null) {
+      throw StateError('Not connected to PostgreSQL');
+    }
+    final result = await _conn!.execute(
+      Sql.named(
+        'SELECT c.reltuples FROM pg_catalog.pg_class c '
+        'JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace '
+        'WHERE n.nspname = @schema AND c.relname = @table '
+        "AND c.relkind IN ('r', 'p', 'm', 'f') "
+        'LIMIT 1',
+      ),
+      parameters: {'schema': schema, 'table': table},
+    );
+    if (result.isEmpty) return null;
+    return postgresReltuplesEstimate(result.first[0]);
+  }
+
   /// Returns primary key column names for [table] in [schema].
   Future<List<String>> getPrimaryKeys({
     String schema = 'public',

lib/core/database/postgres_connection_pool.dart

@@ -7,7 +7,7 @@ import 'package:querya_desktop/core/storage/local_db.dart';
 /// Session policy for pooled connections: browse-only vs ad-hoc SQL (writes).
 enum PgSessionMode {
   /// `SET default_transaction_read_only = ON` after connect.
-  /// Tree catalog, stats, and Table Browser SELECT/COUNT.
+  /// Tree catalog, stats, and Table Browser SELECT.
   readOnly,
 
   /// SQL editor read-write session. Must not be shared with Table Browser.

lib/features/postgresql/postgres_table_utils.dart

@@ -7,6 +7,20 @@ import 'package:querya_desktop/core/database/sql_limit.dart';
 /// Default page size for table browse and the SQL template filled from the tree.
 const kPostgresBrowseDefaultRowLimit = 200;
 
+/// Browse SELECT for Table Browser. PK columns get `ORDER BY` so LIMIT/OFFSET
+/// is stable. Empty [primaryKeys] keeps unordered scan (views / no PK).
+String postgresBrowseDataSql({
+  required String qualifiedFrom,
+  required List<String> primaryKeys,
+  required int limit,
+  required int offset,
+}) {
+  final order = primaryKeys.isEmpty
+      ? ''
+      : ' ORDER BY ${primaryKeys.map(quotePostgresIdentifier).join(', ')}';
+  return 'SELECT * FROM $qualifiedFrom$order LIMIT $limit OFFSET $offset';
+}
+
 /// `SELECT *` template matching [PostgresTableView] browse (same limit/offset).
 String postgresBrowseSelectSql({
   required String schema,

lib/features/postgresql/postgres_table_view.dart

@@ -59,7 +59,7 @@ class _PostgresTableViewState extends material.State<PostgresTableView> {
   /// Rows on the current page (same as _rows.length when not loading).
   int _rowsOnPage = 0;
 
-  /// Total rows in table/view (from COUNT(*)).
+  /// Planner estimate (`reltuples`); `null` when unknown or stale.
   int? _totalRowCount;
 
   /// Zero-based offset for LIMIT/OFFSET pagination.
@@ -182,18 +182,15 @@ class _PostgresTableViewState extends material.State<PostgresTableView> {
     }
   }
 
-  static int _asInt(dynamic v) {
-    if (v == null) return 0;
-    if (v is int) return v;
-    if (v is BigInt) return v.toInt();
-    if (v is num) return v.toInt();
-    return int.tryParse(v.toString()) ?? 0;
-  }
-
   String _browseDataSql() {
     final schemaQ = quotePostgresIdentifier(widget.schema);
     final tableQ = quotePostgresIdentifier(widget.tableName);
-    return 'SELECT * FROM $schemaQ.$tableQ LIMIT ${widget.limit} OFFSET $_offset';
+    return postgresBrowseDataSql(
+      qualifiedFrom: '$schemaQ.$tableQ',
+      primaryKeys: _primaryKeys,
+      limit: widget.limit,
+      offset: _offset,
+    );
   }
 
   Future<T> _withTableWrite<T>(
@@ -275,7 +272,7 @@ class _PostgresTableViewState extends material.State<PostgresTableView> {
     return convertResultRowsToStringsAdaptive(converted);
   }
 
-  /// [refreshCount] runs `COUNT(*)` (e.g. first load or Refresh). Pagination only runs SELECT.
+  /// [refreshCount] re-reads `reltuples` (e.g. first load or Refresh). Pagination only runs SELECT.
   Future<void> _fetch({bool refreshCount = false}) async {
     final conn = _connection;
     if (conn == null || !conn.isConnected) {
@@ -296,25 +293,26 @@ class _PostgresTableViewState extends material.State<PostgresTableView> {
       _loading = true;
       _error = null;
     });
-    final schemaQ = quotePostgresIdentifier(widget.schema);
-    final tableQ = quotePostgresIdentifier(widget.tableName);
-    final countSql = 'SELECT COUNT(*) AS c FROM $schemaQ.$tableQ';
-    final dataSql = _browseDataSql();
     try {
-      int totalRows;
-      if (refreshCount || _totalRowCount == null) {
-        final countResult = await conn.execute(countSql);
-        totalRows = countResult.isEmpty ? 0 : _asInt(countResult.first[0]);
-      } else {
-        totalRows = _totalRowCount!;
+      await _ensureSchema(conn);
+      if (!mounted) return;
+
+      int? totalRows = _totalRowCount;
+      if (refreshCount || totalRows == null) {
+        try {
+          totalRows = await conn.estimateTableRows(
+            schema: widget.schema,
+            table: widget.tableName,
+          );
+        } catch (_) {
+          totalRows = null;
+        }
       }
 
+      final dataSql = _browseDataSql();
       final result = await conn.execute(dataSql);
       if (!mounted) return;
 
-      await _ensureSchema(conn);
-      if (!mounted) return;
-
       final colNames = List<String>.generate(
         result.schema.columns.length,
         (i) => result.schema.columns[i].columnName ?? 'col_$i',
@@ -323,10 +321,14 @@ class _PostgresTableViewState extends material.State<PostgresTableView> {
       final stringRows = await _postgresRowsToDisplayStrings(result, colNames);
 
       if (!mounted) return;
+      final shown = stringRows.length;
+      if (totalRows != null && shown > 0 && totalRows < _offset + shown) {
+        totalRows = null;
+      }
       setState(() {
         _columnNames = colNames;
         _rows = stringRows;
-        _rowsOnPage = stringRows.length;
+        _rowsOnPage = shown;
         if (refreshCount || _totalRowCount == null) {
           _totalRowCount = totalRows;
         }

test/core/database/postgres_connection_string_parse_test.dart

@@ -109,4 +109,14 @@ void main() {
       );
     });
   });
+
+  group('postgresReltuplesEstimate', () {
+    test('rounds planner floats and treats unanalyzed as unknown', () {
+      expect(postgresReltuplesEstimate(200.4), 200);
+      expect(postgresReltuplesEstimate(199.6), 200);
+      expect(postgresReltuplesEstimate(0), 0);
+      expect(postgresReltuplesEstimate(-1), isNull);
+      expect(postgresReltuplesEstimate(null), isNull);
+    });
+  });
 }

test/features/postgresql/postgres_table_utils_test.dart

@@ -90,6 +90,44 @@ void main() {
     });
   });
 
+  group('postgresBrowseDataSql', () {
+    test('orders by quoted PK columns', () {
+      expect(
+        postgresBrowseDataSql(
+          qualifiedFrom: '"public"."orders"',
+          primaryKeys: const ['id'],
+          limit: 200,
+          offset: 400,
+        ),
+        'SELECT * FROM "public"."orders" ORDER BY "id" LIMIT 200 OFFSET 400',
+      );
+    });
+
+    test('composite PK lists all columns', () {
+      expect(
+        postgresBrowseDataSql(
+          qualifiedFrom: '"public"."t"',
+          primaryKeys: const ['a', 'b'],
+          limit: 200,
+          offset: 0,
+        ),
+        'SELECT * FROM "public"."t" ORDER BY "a", "b" LIMIT 200 OFFSET 0',
+      );
+    });
+
+    test('omits ORDER BY when there is no PK', () {
+      expect(
+        postgresBrowseDataSql(
+          qualifiedFrom: '"public"."v"',
+          primaryKeys: const [],
+          limit: 200,
+          offset: 0,
+        ),
+        'SELECT * FROM "public"."v" LIMIT 200 OFFSET 0',
+      );
+    });
+  });
+
   group('convertResultRowsToStrings', () {
     test('converts null to "NULL"', () {
       final result = convertResultRowsToStrings([