Basic rate limiter using ScyllaDB. How?

I want to use Scylla to write simple rate limiter (because I already use Scylla and don’t want to add another DB just for that).

Counters look like a good tool for that, however they don’t have any kind of expiration. I already solved similar problem, where I need a limit per day. I basically create table every day and use it for writes, then create new one and use that (the old is deleted via cronjob).

Now I want to rate limit requests per minute, so it’s not a good solution. I can use something like that:

create table rate_limiter (
  id ascii,
  slot int,
  cu_used counter,
  PRIMARY KEY (id, slot)

Where slot is basically a time slot (say floor(unixtime/60)). It would be enough, but of course I need some expiration. I could probably do the same, create new table every day, delete the old one. However, this looks messy and I don’t like that at all.

  • I could probably use something other than counters, but only the have increments.
  • Inserting a row per request looks like too much overhead for rate limiting

Are there any better solutions?

The underlying problem here is that counters don’t support expiry. So you either have to switch to a data type which does support expiry (basically anything apart from counters), or you need another cron job which removes rows from this table from time-to-time.