How to improve performance for large datasets with Realm? - swift

Question

My database has 500,000 records. The tables don't have a primary key because Realm doesn't support compound primary keys. I fetch data in background thread, then I want to display it in the UI on the main thread. But since Realm objects cannot be shared across threads I cannot use the record I fetched in the background. Instead I need to refetch the record on main thread? If I fetch a record out of the 500,000 records it will block the main thread. I don't know how to deal with it. I use Realm because it said it's enough quick. If I need refetch the record many times, is it really faster than SQLite? I don't want to create another property that combine other columns as primary key because the Realm database is already bigger than a SQLite file.
#objc class CKPhraseModel: CKBaseHMMModel{
dynamic var pinyin :String!
dynamic var phrase :String = ""
class func fetchObjects(apinyin :String) -> Results<CKPhraseModel> {
let realm = Realm.createDefaultRealm()
let fetchString = generateQueryString(apinyin)
let phrases = realm.objects(self).filter(fetchString).sorted("frequency", ascending: false)
return phrases
}
func save(needTransition :Bool = true) {
if let realm = realm {
try! realm.write(needTransition) {[unowned self] in
self.frequency += 1
}
}
else {
let realm = Realm.createDefaultRealm()
if let model = self.dynamicType.fetchObjects(pinyin).filter("phrase == %#", phrase).first {
try! realm.write(needTransition) {[unowned self] in
model.frequency += self.frequency
}
}
else {
try! realm.write(needTransition) {[unowned self] in
realm.add(self)
}
}
}
}
}
then I store fetched records in Array
let userInput = "input somthing"
let phraseList = CKPhraseModel().fetchObjects(userInput)
for (_,phraseModel) in phraseList.enumerate() {
candidates.append(phraseModel)
}
Then I want to display candidates information in UI when the user clicks one of these. I will call CKPhraseModel's save function to save changes. This step is on main thread.

Answer 1

Realm is fast if you use its lazy loading capability, which means that you create a filter that would return your candidates directly from the Realm, because then you'd need to only retrieve only the elements you index in the results.
In your case, you copy ALL elements out. That's kinda slow, which is why you end up freezing.