Gate Query Store wait stats for SQL 2017+ with capture mode check

src/PlanViewer.App/Controls/QuerySessionControl.axaml.cs

@@ -1021,11 +1021,26 @@ private async void QueryStore_Click(object? sender, RoutedEventArgs e)
 
         SetStatus("");
 
+        // Check if wait stats are supported (SQL 2017+ / Azure) and capture is enabled
+        var supportsWaitStats = _serverMetadata?.SupportsQueryStoreWaitStats ?? false;
+        if (supportsWaitStats)
+        {
+            try
+            {
+                var connStr = _serverConnection!.GetConnectionString(_credentialService, _selectedDatabase!);
+                supportsWaitStats = await QueryStoreService.IsWaitStatsCaptureEnabledAsync(connStr);
+            }
+            catch
+            {
+                supportsWaitStats = false;
+            }
+        }
+
         // Build database list from the current DatabaseBox
         var databases = DatabaseBox.Items.OfType<string>().ToList();
 
         var grid = new QueryStoreGridControl(_serverConnection!, _credentialService,
-            _selectedDatabase!, databases);
+            _selectedDatabase!, databases, supportsWaitStats);
         grid.PlansSelected += OnQueryStorePlansSelected;
 
         var headerText = new TextBlock

src/PlanViewer.App/Controls/QueryStoreGridControl.axaml.cs

@@ -41,6 +41,7 @@ public partial class QueryStoreGridControl : UserControl
     private bool _initialOrderByLoaded;
     private bool _suppressRangeChanged;
     private string? _waitHighlightCategory;
+    private bool _waitStatsSupported;  // false until version + capture mode confirmed
     private bool _waitStatsEnabled = true;
     private bool _waitPercentMode;
 
@@ -50,12 +51,13 @@ public partial class QueryStoreGridControl : UserControl
     public string Database => _database;
 
     public QueryStoreGridControl(ServerConnection serverConnection, ICredentialService credentialService,
-        string initialDatabase, List<string> databases)
+        string initialDatabase, List<string> databases, bool supportsWaitStats = false)
     {
         _serverConnection = serverConnection;
         _credentialService = credentialService;
         _database = initialDatabase;
         _connectionString = serverConnection.GetConnectionString(credentialService, initialDatabase);
+        _waitStatsSupported = supportsWaitStats;
         _slicerDaysBack = AppSettingsService.Load().QueryStoreSlicerDays;
         InitializeComponent();
         ResultsGrid.ItemsSource = _filteredRows;
@@ -69,6 +71,19 @@ public QueryStoreGridControl(ServerConnection serverConnection, ICredentialServi
         WaitStatsProfile.CategoryDoubleClicked += OnWaitCategoryDoubleClicked;
         WaitStatsProfile.CollapsedChanged += OnWaitStatsCollapsedChanged;
 
+        if (!_waitStatsSupported)
+        {
+            // Hide wait stats panel and column when server doesn't support it
+            WaitStatsProfile.Collapse();
+            WaitStatsChevronButton.IsVisible = false;
+            WaitStatsSplitter.IsVisible = false;
+            SlicerRow.ColumnDefinitions[2].Width = new GridLength(0);
+            var waitProfileCol = ResultsGrid.Columns
+                .FirstOrDefault(c => c.SortMemberPath == "WaitGrandTotalSort");
+            if (waitProfileCol != null)
+                waitProfileCol.IsVisible = false;
+        }
+
         // Auto-fetch with default settings on connect
         Avalonia.Threading.Dispatcher.UIThread.Post(() =>
         {
@@ -192,7 +207,7 @@ private async System.Threading.Tasks.Task FetchPlansForRangeAsync()
             SelectToggleButton.Content = "Select None";
 
             // Fetch wait stats in parallel (non-blocking for plan display)
-            if (_waitStatsEnabled && _slicerStartUtc.HasValue && _slicerEndUtc.HasValue)
+            if (_waitStatsSupported && _waitStatsEnabled && _slicerStartUtc.HasValue && _slicerEndUtc.HasValue)
                 _ = FetchWaitStatsAsync(_slicerStartUtc.Value, _slicerEndUtc.Value, ct);
         }
         catch (OperationCanceledException)
@@ -460,7 +475,7 @@ private void OnWaitStatsCollapsedChanged(object? sender, bool collapsed)
         if (waitProfileCol != null)
             waitProfileCol.IsVisible = !collapsed;
 
-        if (!collapsed && _slicerStartUtc.HasValue && _slicerEndUtc.HasValue)
+        if (!collapsed && _waitStatsSupported && _slicerStartUtc.HasValue && _slicerEndUtc.HasValue)
         {
             // Re-fetch wait stats when expanding — reuse the shared CTS
             var ct = _fetchCts?.Token ?? CancellationToken.None;

src/PlanViewer.Core/Models/ServerMetadata.cs

@@ -28,6 +28,12 @@ public class ServerMetadata
     /// </summary>
     public bool SupportsScopedConfigs =>
         IsAzure || (int.TryParse(ProductVersion?.Split('.')[0], out var major) && major >= 13);
+
+    /// <summary>
+    /// Whether sys.query_store_wait_stats is available (SQL 2017+ or Azure).
+    /// </summary>
+    public bool SupportsQueryStoreWaitStats =>
+        IsAzure || (int.TryParse(ProductVersion?.Split('.')[0], out var major) && major >= 14);
 }
 
 public class DatabaseMetadata

src/PlanViewer.Core/Services/QueryStoreService.cs

@@ -427,6 +427,36 @@ GROUP BY DATEADD(HOUR, DATEDIFF(HOUR, 0, rsi.start_time), 0)
 
     // ── Wait stats ─────────────────────────────────────────────────────────
 
+    /// <summary>
+    /// Checks whether Query Store wait stats capture is enabled for the connected database.
+    /// Returns false on SQL Server 2016 (where the option doesn't exist) or when capture is OFF.
+    /// </summary>
+    public static async Task<bool> IsWaitStatsCaptureEnabledAsync(
+        string connectionString, CancellationToken ct = default)
+    {
+        const string sql = @"
+SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
+SELECT CASE
+    WHEN EXISTS (
+        SELECT 1 FROM sys.database_query_store_options
+        WHERE wait_stats_capture_mode_desc = 'ON'
+    ) THEN 1 ELSE 0 END;";
+
+        try
+        {
+            await using var conn = new SqlConnection(connectionString);
+            await conn.OpenAsync(ct);
+            await using var cmd = new SqlCommand(sql, conn) { CommandTimeout = 10 };
+            var result = await cmd.ExecuteScalarAsync(ct);
+            return result is int i && i == 1;
+        }
+        catch
+        {
+            // Column doesn't exist on SQL 2016, or query store not enabled
+            return false;
+        }
+    }
+
     // Excluded: 11 = Idle, 18 = User Wait
     private const string WaitCategoryExclusion = "AND ws.wait_category NOT IN (11, 18)";