Producer c waits outside a full two-slot queue holding a and b. An outgoing path shows that get(a) frees a slot, permitting c to enter.

Backpressure works when bounded admission changes the producer’s behavior

Backpressure connects a consumer’s limited capacity to the behavior of its producers. A full channel may make a producer wait, reject new work, or apply a deliberately chosen shedding policy. The important property is that the limit changes what upstream components do. A growing queue or a dashboard showing lag is evidence of imbalance, but neither is automatically a mechanism that controls admission. ...

August 12, 2027 · 5 min · XB Field Notes
A retry enters one transaction boundary enclosing an operation identity and its business effect.

Protect the committed effect: schematic.

Queues define delivery; consumers must protect effects

A queue’s delivery promise describes a bounded part of a workflow. Getting a message to a consumer is different from committing its business effect. At-least-once delivery allows redelivery; at-most-once delivery permits loss rather than retrying uncertain delivery. Neither label alone guarantees that an order, notification, or database update completes exactly once under every failure. ...

February 5, 2027 · 5 min · XB Field Notes