I discussed with @tomek what would be the best approach here to get cookie ids associated with relevant device tokens necessary to encrypt notifications. We considered three different approaches:

1. Modify the SQL query present at the beginning of this function to JOIN with cookies table based on user field and then extract cookie ids for device tokens. We didn't choose this approach since the resulting query would return many irrelevant cookie ids that we would have to manually filter.
2. Use JSON_EXTRACT on the delivery to get device_tokens and then somehow get relevant cookie ids using JOIN or sub queries. We didn't choose this approach since such query could potentially be extremely complicated and probably unmaintainable in future.

Therefore we decided it is best to issue additional query where to get relevant cookie ids based on device tokens returned from previous query. This approach does not necessarily have to be poorer in terms of performance but it does force use iterate over fetchResults twice. (first to get cookie ids and device tokens, second to use cookie ids and device tokens to encrypt and send rescinds.)

if there is a disagreement as to whether the approach above is correct, I would rather refactor the way we store data contained within delivery field into something relational. That would allow us to modify the original query to use JOIN to easily get relevant cookie ids.

Why do we use warning level? For me these are at most info, probably even just debug.

My bad. I left logs I used for debugging. I will remove them since they are of no use here.

Great use of a type parameter!

This can be defined lower, eg. before the for loop on line 196

Please match existing SQL query format style in the codebase

If a couple of notifications are sent to the same device then we indeed can have multiple same deviceToken. Each row in notifications table contains delivery column which contains all device tokens this notification was successfully sent to.

Therefore using a set here should be functionally equivalent to raw array. We eventually create a map deviceToken => cookieID. Database schema enforces that each cookieID corresponds to exactly one deviceToken. I am not sure about the performance here. Adding to an array (at the end) should be faster that adding to a set, but using a set could speed up SQL query that lookups cookieIDs. Therefore we can use a Set here.

It is my oversight. I should have added await in both.

This would require us to modify prepareEncryptedAndroidNotifications and prepareEncrypted

It is my oversight. I forgot to remove debugging logs.

According to docs: https://mariadb.com/kb/en/in/ MariaDB sorts list passed to IN and then does binary search on it. Therefore using a Set will let us pass shorter list and therefore improve performance.