The cost of deletions is heavy, and I wouldn't have done it this way, but note that where it really matters is if you have to do this repeatedly in a loop. But

The cost of deletions is heavy, and I wouldn't have done it this way, but note that where it really matters is if you have to do this repeatedly in a loop. But you don't have to do it repeatedly -- you can just delete a ton of messages at once, at the same cost as deleting a single once. As long as user perceptions go, the network latency is probably going to dominate shifting down even a million integers (< 2 ms on my machine), which I suspect most people don't even have.