Limits and rate limits

Limit{Key, Max} caps how many jobs sharing a key can be processing at once, across the whole cluster, independent of queue or worker pool. A job over the cap sits in throttled until a slot frees up. This is kiln's equivalent of Hangfire's DisableConcurrentExecution and Hangfire Ace's semaphores, without needing a separate package.

Rate and Per cap how many jobs of a key may start per period, and Burst how many may start back to back (it defaults to Rate). When a job is admitted kiln reserves its start time, so a backlog of 10,000 jobs against a 100/s limit is released at that pace, each job written once, instead of being retried until it fits:

client.Enqueue(ctx, ChargeCard{OrderID: id}, kiln.Limit{Key: "stripe", Rate: 100, Per: time.Second})

Max and Rate can be combined on one key: Max bounds how many run at once, Rate how often they start.

The rate also holds when kiln falls behind. If admission stalls for a while, because the database was slow or a lock was held, the jobs whose start times passed in the meantime don't all start when it resumes: Burst of them start and the rest get new start times at the back of the line. No window of length Per sees more than Rate + Burst starts of a key.