Check if email exists in user list using AngularFire2 - firebase

Question

I want to check if there exists a user that have email = someemail#gmai.com in the Firebase database.
I use this function and is download 50MB of data in my PC after 10 minute I get a response that exists. There is any way that I can get that less than 5 second I don't want to wait 10 minute.
in PHP is like the
SELECT FROM ALL USERS WERE EMAIL = 'george#gmail.com'
This is the database:
"users" : {
user: {
"email" : "george#gmail.com",
"custom_id" : 534253,
"description" : "some small description"
},
1754: {
"email" : "natassa#gmail.com", <---- i want to find if this email from 5000 users exist in database and if exist i want to return true
"custom_id" : 110571,
"description" : "some small description"
},
1755: {
"email" : "george#gmail.com",
"custom_id" : dsgfsdfds,
"description" : "some small description"
},
}
This function give me response after 10 min:
check_if_email_exist(email: string) {
this.users = this.db.list('/user', { query: {
orderByChild: 'email',
equalTo: x,
limitToLast: 10,
}} ) as FirebaseListObservable<Product[]>;
console.log(this.users);
return this.users;
}

Answer 1

OMG I find the problem thanx to https://stackoverflow.com/users/209103/frank-van-puffelen is say something about index and when I look in my chrome console I find warning that says something about index and when I look in the database rules I understand what is missing
I add this inside database rules
{
"rules": {
".read": "auth != null",
".write": "auth != null",
"needs": {
".read": "true",
".write": "auth != null",
".indexOn": "name"
},
"brands": {
".read": "true",
".write": "auth != null",
".indexOn": "name"
},
"products": {
".read": "true",
".write": "auth != null",
".indexOn": "custom_id" <========== This line you want
}
}
}