Small improvements

app/src/main/java/eu/faircode/email/DB.java

@@ -110,9 +110,9 @@ public abstract class DB extends RoomDatabase {
             Helper.getBackgroundExecutor(1, "query");
 
     private static final String DB_NAME = "fairemail";
-    private static final int DB_CHECKPOINT = 100;
+    private static final int DB_CHECKPOINT = 1000; // requery/sqlite-android default
 
-    static final String[] DB_TABLES = new String[]{
+    private static final String[] DB_TABLES = new String[]{
             "identity", "account", "folder", "message", "attachment", "operation", "contact", "certificate", "answer", "rule", "log"};
 
     @Override
@@ -179,7 +179,7 @@ public abstract class DB extends RoomDatabase {
                 .databaseBuilder(context, DB.class, DB_NAME)
                 .openHelperFactory(new RequerySQLiteOpenHelperFactory())
                 .setQueryExecutor(executor)
-                .setJournalMode(JournalMode.WRITE_AHEAD_LOGGING)
+                .setJournalMode(JournalMode.WRITE_AHEAD_LOGGING) // using the latest sqlite
                 .addCallback(new Callback() {
                     @Override
                     public void onOpen(@NonNull SupportSQLiteDatabase db) {