Is it possible to apply a mixed retention policy about messages deletion on kafka mixing log.retention.bytes and log retention.hours? What i'm trying to do is keeping in queue a certain size of log but delete on time expire anyway even if the size is under the given upper bound
Yes you can mix both time and size retention settings. Whichever applies first will trigger the deletion.
So yes, for your example, logs would be cleaned even if you don't reach the max size but just wait for the time to expire.