java – Query Firebase from Android app downloads a lot of data

Question:

I am querying Firebase from an Android app. The queries are as follows.

Consultation 1

reference.orderByChild("started").equalTo(true).addValueEventListener(new ValueEventListener() {...}

This query returns 5 results, but the consumption is 1.5 MB. It's like it returns all records. What can be happening?

I have done another test, with the following query, that data consumption does not occur:

Consultation 2

reference.limitToLast(5).addValueEventListener(new ValueEventListener() {...}

It also returns 5 records, but in this case it consumes only 10 KB .

How could I perform the first query without this excessive data consumption?

The consulted database has about 1500 records.

The database structure is this:

Game: 
          -KW_-cgwIPt5E8lzguds:
                               nivel1: array
                               nivel2: array
                               nivel3: array
                               nivel4: array
                               jugador1: String
                               jugador1Pts: int
                               jugador2: String
                               jugador2Pts: int
                               jugador1End: boolean
                               jugador2End: boolean
                               started: boolean
                               completed: boolean
          -KW_-cgwIPt5E8lztyd5:
                               nivel1: array
                               ....

And the full code is:

reference.orderByChild("started").equalTo(true)..addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            gameOnList.clear();
                for (DataSnapshot gamesSnapshot : dataSnapshot.getChildren()){
                    Game game = gamesSnapshot.getValue(Game.class);
                    if(game.isStarted()) gameOnList.add(game);
                }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });

Answer:

The startAt(),endAt() and equalTo() operators have to traverse the entire array to filter it, in your case 1500 records. These operators have to be accompanied by an index in this node, thus facilitating the search.

{
 "rules": {
 "tuNodo": {
  ".indexOn": ".tuValor"
  }
 }
}

This would greatly reduce data consumption and execution time. If you want more information on how to index the data, take a look at this page . If it is still high, we would have to look at the option to denormalize the data. All the best!