Why is Datastore slower than Shared Preferences

Question

I was checking the execution time of datastore and shared preference and I observed that datastore takes more time than shared preference.

This is my code

suspend fun saveUser(user: User, context: Context) {
            val userString =
                Json.encodeToString(User.serializer(), user)
            val time1 = System.nanoTime()
            context.dataStore.edit { preferences ->
                preferences[PreferencesKeys.USER] = userString
            }
            val time2 = System.nanoTime()
            with(userPref.edit()) {
                putString(HOME_USER_KEY, userString)
                apply()
            }
            val time3 = System.nanoTime()
            println("Time taken")
            println("Datastore : ${time2 - time1}")
            println("Shared Preferences : ${time3 - time2}")
        }

And the output

I/System.out: Time taken
I/System.out: Datastore : 208257769
I/System.out: Shared Preferences : 14458539

I/System.out: Time taken
I/System.out: Datastore : 2892692
I/System.out: Shared Preferences : 246462

I/System.out: Time taken
I/System.out: Datastore : 3043770
I/System.out: Shared Preferences : 293846

I/System.out: Time taken
I/System.out: Datastore : 5548077
I/System.out: Shared Preferences : 321846

I/System.out: Time taken
I/System.out: Datastore : 2344076
I/System.out: Shared Preferences : 208616

Any idea of why this might be happening?

Answer 1

Because data store has additional layers of thread safety - in this case edit { } is suspending function that switches the dispatcher "under the hood" and waits until the disk write is actually complete.

SharedPreferences apply doesn't do that - it stores changes in-memory while starting async disk write that you don't have control over nor can you handle any errors.