Transloadit

What is a Priority Job Slot?

A Priority Job Slot is one unit of the Live Queue processing capacity included with a Transloadit subscription plan. Every Robot type has a fixed, documented slot cost: a /video/encode job occupies 60 slots, while an /image/resize job occupies 5. A Workspace’s slot allowance applies separately in each region.

How Priority Job Slots work

Priority Job Slots express weighted scheduler capacity rather than a simple count of active jobs. Each job’s cost is a fixed value configured for its Robot type, with only a few Robots varying the cost by their Instructions. A few expensive video jobs can therefore consume more of the allowance than many lightweight image jobs. Exceeding the allowance does not fail work: excess live jobs trickle down into the Backup Queue and are automatically re-enqueued as running jobs complete and free slots. This allowance is separate from the Rate Limiter’s Assembly-creation limits, so a workload can stay under those limits and still queue for slots.

Key facts

  1. Slot costs are published constants per Robot type. /video/encode currently costs 60 slots, the highest entry in the table, while /image/resize costs 5 and /s3/store costs 2. These values let you calculate required capacity instead of estimating it.
  2. The slot allowance comes from the subscription plan and acts per Workspace and per region: a plan with 500 Priority Job Slots provides 500 in each region Transloadit operates in, not one global pool.
  3. Sending more live jobs than the allowance covers does not reject them; the excess trickles down into the Backup Queue and returns to the Live Queue as soon as completed jobs free up the Workspace’s slots.

When Priority Job Slots matter

Sum the documented slot costs of the Robots your workload runs concurrently to predict when jobs will start queueing, and reserve a higher allowance before a predictable surge. Steps that do not need real-time processing can set "queue": "batch" so their jobs avoid consuming Priority Job Slots.

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