I wonder how we could handle that in a simpler way with durable workflows (e.g. Temporal, Restante, DBOS) – which are similar to Erlang processes but with persistent disk storage. This could avoid the need to maintain the 1000 row inventory.

Perhaps each shopping cart would have its own workflow, and the inventory item would have one as well. Then, whenever a customer put an item in their cart, their cart workflow would send a signal to the inventory item workflow and wait for the response. The inventory item workflow would maintain a ledger controlling to which cart each unit goes, and it could batch the writes to this table. This way, even if 100k customers try to purchase the same item in the same second, it should handle the load.

After the batch is written to the ledger, the inventory item workflow would reply signals to each cart workflow confirming that the reservation was completed. The end-to-end latency from the consumer point of view would be a fraction of a second, without needing the 1000-row hot-inventory heuristic.