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Frequently Asked Questions

How can I guarantee message order?​

Even though Querator is a FIFO queue, order cannot be guaranteed if multiple consumers pull from the same queue, as consumers may receive ordered items simultaneously, thus losing order.

Consider a scenario with two consumers accessing a FIFO queue:

  • Consumer 1 retrieves an item.
  • Consumer 2 retrieves an item.
  • Consumer 2 finishes processing their item.
  • Consumer 1 finishes processing their item.

In this situation, the system -— which includes the entire setup of client producers, Querator, and client consumers -— cannot reliably maintain the order of item processing when multiple consumers are involved. To ensure ordered processing, items which require preservation of order should be placed in the same queue, and that queue must have only one partition and one consumer.

To guarantee message order, create a queue with a single partition and a single consumer that leases items from the queue. You can scale this approach by creating multiple queues, each with a single partition and a single consumer. An alternative is use a lock service that refuses to process any leased items if the lock is currently held by another consumer.