Perhaps you could encrypt your logs after a predefined “live data” period passes. Each log line’s key would be derived from a key that is itself derived from the data subject’s unique identifier. If that subject invokes their “right to be forgotten” then the subject’s key is destroyed, rendering all thus-encrypted log lines irretrievable. This does mean analysis of “cold logs” would first require a potentially burdensome decryption process — but it would be possible, and the resulting logs would only contain data relating to permitted data subjects.