Design a service waitlist that makes the next offer clear

Separate waiting from holding a place

PostgreSQL's locking reference describes how concurrent operations can be prevented from modifying the same locked row simultaneously. For a waitlist, the important requirement is that two operators cannot accidentally offer the same exclusive place to different people. First define the states: waiting, offered, accepted, expired and withdrawn. Joining the waitlist should not imply a confirmed place.

Choose the allocation rule. It could be order of arrival, service compatibility or a manual decision by the owner. Explain the rule to staff and, where appropriate, customers. If priorities exist, record why an entry receives them instead of hiding the decision in an unexplained sort order.

• PostgreSQL: explicit locking ↗

Give every offer a boundary

An offer should name the available service, the person receiving it and the response deadline if one applies. Decide whether the place is held during that window. A message that says 'a place is available' means something different from an exclusive offer that reserves it temporarily.

Define what the customer sees if they respond late. They might return to the queue or be offered a different opening, but the app should not silently accept an expired promise. Include a clear route for declining so staff do not have to wait for every offer to time out.

Handle the queue's ordinary exceptions

People may join twice, change availability or become unreachable. Decide how to match repeated entries without excluding two people who share a name. Allow staff to record a contact problem and move an entry through the agreed process while preserving the reason for the decision.

Treat message sending and offer creation as related but separate outcomes. If a notification fails, the owner needs to see that the person may not know about the offer. Decide whether the deadline pauses, the offer is retried or staff use another approved contact route.

Test a complete release of capacity

Create a sample queue and release one place. Confirm that the correct person receives the offer, accepts it and becomes the confirmed participant. Then repeat with a decline and an expiry. The next person should move forward exactly as the chosen policy describes.

Also have two staff members try to release the same place. Inspect the resulting offers and reservations, not only the messages on their screens. A useful waitlist app makes allocation, timing and exceptions explainable, so customers and staff can understand why a place is still waiting or has moved on.