Fixed: Performance issue when scanning large root folder

src/NzbDrone.Common/Disk/DiskProviderBase.cs

@@ -149,6 +149,13 @@ namespace NzbDrone.Common.Disk
             }
         }
 
+        public bool FolderEmpty(string path)
+        {
+            Ensure.That(path, () => path).IsValidPath();
+
+            return _fileSystem.Directory.EnumerateFileSystemEntries(path).Empty();
+        }
+
         public string[] GetDirectories(string path)
         {
             Ensure.That(path, () => path).IsValidPath();

src/NzbDrone.Common/Disk/IDiskProvider.cs

@@ -22,6 +22,7 @@ namespace NzbDrone.Common.Disk
         bool FileExists(string path);
         bool FileExists(string path, StringComparison stringComparison);
         bool FolderWritable(string path);
+        bool FolderEmpty(string path);
         string[] GetDirectories(string path);
         string[] GetFiles(string path, SearchOption searchOption);
         long GetFolderSize(string path);

src/NzbDrone.Core.Test/MediaFiles/DiskScanServiceTests/ScanFixture.cs

@@ -9,6 +9,7 @@ using FluentAssertions;
 using Moq;
 using NUnit.Framework;
 using NzbDrone.Common.Disk;
+using NzbDrone.Common.Extensions;
 using NzbDrone.Core.DecisionEngine;
 using NzbDrone.Core.MediaFiles;
 using NzbDrone.Core.MediaFiles.TrackImport;
@@ -139,7 +140,7 @@ namespace NzbDrone.Core.Test.MediaFiles.DiskScanServiceTests
             ExceptionVerification.ExpectedWarns(1);
 
             Mocker.GetMock<IDiskProvider>()
-                  .Verify(v => v.FolderExists(_artist.Path), Times.Never());
+                  .Verify(v => v.GetFiles(_artist.Path, SearchOption.AllDirectories), Times.Never());
 
             Mocker.GetMock<IMediaFileTableCleanupService>()
                   .Verify(v => v.Clean(It.IsAny<string>(), It.IsAny<List<string>>()), Times.Never());

src/NzbDrone.Core/MediaFiles/DiskScanService.cs

@@ -95,25 +95,28 @@ namespace NzbDrone.Core.MediaFiles
                     return;
                 }
 
-                if (!_diskProvider.FolderExists(rootFolder.Path))
-                {
-                    _logger.Warn("Root folder {0} doesn't exist.", rootFolder.Path);
-
-                    var skippedArtists = _artistService.GetArtists(artistIds);
-                    skippedArtists.ForEach(x => _eventAggregator.PublishEvent(new ArtistScanSkippedEvent(x, ArtistScanSkippedReason.RootFolderDoesNotExist)));
-                    return;
-                }
+                var folderExists = _diskProvider.FolderExists(folder);
 
-                if (_diskProvider.GetDirectories(rootFolder.Path).Empty())
+                if (!folderExists)
                 {
-                    _logger.Warn("Root folder {0} is empty.", rootFolder.Path);
-
-                    var skippedArtists = _artistService.GetArtists(artistIds);
-                    skippedArtists.ForEach(x => _eventAggregator.PublishEvent(new ArtistScanSkippedEvent(x, ArtistScanSkippedReason.RootFolderIsEmpty)));
-                    return;
+                    if (!_diskProvider.FolderExists(rootFolder.Path))
+                    {
+                        _logger.Warn("Artists' root folder ({0}) doesn't exist.", rootFolder);
+                        var skippedArtists = _artistService.GetArtists(artistIds);
+                        skippedArtists.ForEach(x => _eventAggregator.PublishEvent(new ArtistScanSkippedEvent(x, ArtistScanSkippedReason.RootFolderDoesNotExist)));
+                        return;
+                    }
+
+                    if (_diskProvider.FolderEmpty(rootFolder.Path))
+                    {
+                        _logger.Warn("Artists' root folder ({0}) is empty.", rootFolder);
+                        var skippedArtists = _artistService.GetArtists(artistIds);
+                        skippedArtists.ForEach(x => _eventAggregator.PublishEvent(new ArtistScanSkippedEvent(x, ArtistScanSkippedReason.RootFolderIsEmpty)));
+                        return;
+                    }
                 }
 
-                if (!_diskProvider.FolderExists(folder))
+                if (!folderExists)
                 {
                     _logger.Debug("Specified scan folder ({0}) doesn't exist.", folder);