Peter Chow
While using web sdk, it will throw a warning if the code is trying to query data using unspecified index on filtering. It will say something like this
FIREBASE WARNING: Using an unspecified index. Your data will be downloaded and filtered on the client. Consider adding ".indexOn": "yourSortKey" at /data/path to your security rules for better performance.
But this is missing in v3. It would be great to still show this warning somehow to remind the users.
December 28, 2017