Add an index on tracks (album_id)

use subqueries instead of a left join

db/migrations.go

@@ -72,6 +72,7 @@ func (db *DB) Migrate(ctx MigrationContext) error {
 		construct(ctx, "202311072309", migrateAlbumInfo),
 		construct(ctx, "202311082304", migrateTemporaryDisplayAlbumArtist),
 		construct(ctx, "202312110003", migrateAddExtraIndexes),
+		construct(ctx, "202405251900", migrateTrackAddIndexOnAlbumID),
 	}
 
 	return gormigrate.
@@ -813,3 +814,9 @@ func migrateAddExtraIndexes(tx *gorm.DB, _ MigrationContext) error {
 		CREATE INDEX idx_artist_appearances_album_id ON "artist_appearances" (album_id);
 	`).Error
 }
+
+func migrateTrackAddIndexOnAlbumID(tx *gorm.DB, _ MigrationContext) error {
+	return tx.Exec(`
+		CREATE INDEX idx_tracks_album_id ON "tracks" (album_id, length);
+	`).Error
+}

server/ctrlsubsonic/handlers_by_folder.go

@@ -174,8 +174,9 @@ func (c *Controller) ServeGetAlbumList(r *http.Request) *spec.Response {
 	// TODO: think about removing this extra join to count number
 	// of children. it might make sense to store that in the db
 	q.
-		Select("albums.*, count(tracks.id) child_count, sum(tracks.length) duration").
-		Joins("LEFT JOIN tracks ON tracks.album_id=albums.id").
+		Select(`albums.*,
+			(SELECT count(*) FROM tracks WHERE album_id = albums.id) child_count,
+			(SELECT sum(length) FROM tracks WHERE album_id = albums.id) duration`).
 		Group("albums.id").
 		Joins("JOIN album_artists ON album_artists.album_id=albums.id").
 		Offset(params.GetOrInt("offset", 0)).

server/ctrlsubsonic/handlers_internet_radio_test.go

@@ -86,7 +86,7 @@ func runTestCase(t *testing.T, h handlerSubsonic, q url.Values, admin bool) *spe
 		}
 
 		var jsonUnmarshalTypeError *json.UnmarshalTypeError
-		if errors.As(err, &jsonSyntaxError) {
+		if errors.As(err, &jsonUnmarshalTypeError) {
 			t.Fatalf("invalid type at offset %v\n %s <--", jsonUnmarshalTypeError.Offset, body[0:jsonUnmarshalTypeError.Offset])
 		}