Exploring the difference of fetching contact identifiers (CNContactIdentifierKey) vs multiple fields (CNContactPhoneNumbersKey ,CNContactGivenNameKey, etc.).
AddressBook abscess should be granted.
Open swift-fetch-contacts-benchmark/ContactFetchApp/ContactFetchApp.xcodeproj, select scheme ContactFetchApp and run the app. Select key set to fetch, tap Fetch Contacts button and see measured time.