Correct way to append value to serialized array in key_value table I have a serialized array in the value field of key_value, to which I constantly what to append values. An easy way to do this is to get the array, append the new value, and reinsert it. However, with a large enough array it's quite inefficient and in theory it can be done on an SQL level.

What's the correct way to do this in Drupal 8? Is there a way that does not involve getting and then setting the array?
The best way to go about doing this is by using config API. If somehow this option is not suitable for your use case. You can also use the DB API to update the desired congratulation table records. In both cases, you will need to unserialize the blob then change the data and serialize it back before inserting it into the database.

https://www.drupal.org/docs/8/api/configuration-api/configuration-api-overview