Fair queueing, explained with three customers

Picture three customers. One sends 40 jobs, then two others send 8 and 3.

FIFO

With a first-in, first-out queue and four workers, the small customers wait for all 40 jobs to clear. Their p95 wait is the length of the burst.

Fair per key

With a concurrency key on the account, workers take turns across accounts. The small customers start within a second; the big import still finishes.

One line

concurrency: { limit: 4, key: “event.accountId” }