library: stop artist art updates from reindexing artist search

The materialized art update rewrote every artist row on every library-changing sync. That fired the FTS5 content-sync triggers for each artist, which was the real cost: the same SQL is ~10ms with the triggers removed and ~4.7s for 100 changed artists with them in place. Only update rows whose cover lists actually changed, and replace the generated artist search triggers with UPDATE OF name, sortName so art-only writes never touch the FTS index. Existing databases get this through migration 36->37; fresh databases get it from the onCreate callback.

app/src/main/kotlin/com/subtracks/data/db/Databases.kt

@@ -11,6 +11,7 @@ fun createAndroidDatabase(context: Context): SubtracksDatabase {
         .databaseBuilder<SubtracksDatabase>(context, "subtracks.db")
         .setDriver(driver)
         .addMigrations(*MIGRATIONS.map(::LoggedMigration).toTypedArray())
+        .addCallback(ArtistSearchTriggerOptimization)
         .addCallback(SqliteLifecycleLogging)
         .build()
 }

app/src/main/kotlin/com/subtracks/data/db/DbLogging.kt

@@ -114,6 +114,12 @@ class LoggedMigration(
     }
 }
 
+internal object ArtistSearchTriggerOptimization : RoomDatabase.Callback() {
+    override suspend fun onCreate(connection: SQLiteConnection) {
+        optimizeArtistSearchTriggers(connection)
+    }
+}
+
 internal object SqliteLifecycleLogging : RoomDatabase.Callback() {
     override suspend fun onCreate(connection: SQLiteConnection) {
         Log.i("sql", "created fresh database")

app/src/main/kotlin/com/subtracks/data/db/LibraryDao.kt

@@ -230,7 +230,10 @@ internal const val ARTIST_ART_UPDATE_SQL =
         "coverArts = COALESCE((SELECT coverArts FROM covers WHERE covers.artistId = artists.id), ''), " +
         "downloadedCoverArts = COALESCE((SELECT coverArts FROM downloaded_covers " +
         "WHERE downloaded_covers.artistId = artists.id), '') " +
-        "WHERE sourceId = :sourceId"
+        "WHERE sourceId = :sourceId AND (" +
+        "coverArts != COALESCE((SELECT coverArts FROM covers WHERE covers.artistId = artists.id), '') " +
+        "OR downloadedCoverArts != COALESCE((SELECT coverArts FROM downloaded_covers " +
+        "WHERE downloaded_covers.artistId = artists.id), ''))"
 
 internal const val DOWNLOADED_ARTIST_ART_UPDATE_SQL =
     "WITH downloaded_albums AS (SELECT DISTINCT artistId, albumId FROM ($DOWNLOADED_COVER_ALBUM_ROWS) " +
@@ -248,7 +251,9 @@ internal const val DOWNLOADED_ARTIST_ART_UPDATE_SQL =
         ") GROUP BY artistId) " +
         "UPDATE artists SET downloadedCoverArts = COALESCE((SELECT coverArts FROM downloaded_covers " +
         "WHERE downloaded_covers.artistId = artists.id), '') " +
-        "WHERE sourceId = :sourceId AND id IN (:artistIds)"
+        "WHERE sourceId = :sourceId AND id IN (:artistIds) AND " +
+        "downloadedCoverArts != COALESCE((SELECT coverArts FROM downloaded_covers " +
+        "WHERE downloaded_covers.artistId = artists.id), '')"
 
 internal const val ARTISTS_FILTER =
     "FROM artists WHERE sourceId = :sourceId " +

app/src/main/kotlin/com/subtracks/data/db/Migrations.kt

@@ -705,6 +705,29 @@ val MIGRATION_35_36 =
         }
     }
 
+val MIGRATION_36_37 =
+    object : Migration(36, 37) {
+        override suspend fun migrate(connection: SQLiteConnection) {
+            optimizeArtistSearchTriggers(connection)
+        }
+    }
+
+internal fun optimizeArtistSearchTriggers(connection: SQLiteConnection) {
+    connection.execSQL("DROP TRIGGER IF EXISTS room_fts_content_sync_artist_search_BEFORE_UPDATE")
+    connection.execSQL("DROP TRIGGER IF EXISTS room_fts_content_sync_artist_search_AFTER_UPDATE")
+    connection.execSQL(
+        "CREATE TRIGGER IF NOT EXISTS room_fts_content_sync_artist_search_BEFORE_UPDATE " +
+            "BEFORE UPDATE OF `name`, `sortName` ON `artists` BEGIN " +
+            "DELETE FROM `artist_search` WHERE `rowid`=OLD.`rowid`; END",
+    )
+    connection.execSQL(
+        "CREATE TRIGGER IF NOT EXISTS room_fts_content_sync_artist_search_AFTER_UPDATE " +
+            "AFTER UPDATE OF `name`, `sortName` ON `artists` BEGIN " +
+            "INSERT INTO `artist_search`(`rowid`, `name`, `sortName`) " +
+            "VALUES (NEW.`rowid`, NEW.`name`, NEW.`sortName`); END",
+    )
+}
+
 private suspend fun backfillArtistArt(connection: SQLiteConnection) {
     val sourceIds = mutableListOf<Long>()
     connection.prepare("SELECT id FROM sources").use { statement ->
@@ -755,4 +778,5 @@ val MIGRATIONS: Array<Migration> =
         MIGRATION_33_34,
         MIGRATION_34_35,
         MIGRATION_35_36,
+        MIGRATION_36_37,
     )

app/src/main/kotlin/com/subtracks/data/db/SubtracksDatabase.kt

@@ -57,7 +57,7 @@ import com.subtracks.data.model.UpNextEntry
         SongDownload::class,
         PendingAction::class,
     ],
-    version = 36,
+    version = 37,
     exportSchema = true,
 )
 @ColumnTypeConverters(