A consumer calls the payment provider to charge a card, then writes the message id to a "processed" table, then acknowledges. It crashes after the charge. What happens, and what fixes it?

Options

• ✗ Nothing: the message is lost, so nothing is charged twice
• ✗ The broker detects the crash and skips the message
• ✓ The message is redelivered and charged again; pass the message id as the provider's idempotency key Correct
• ✗ The charge is rolled back automatically

Why

A side effect outside your database cannot share a transaction with the "processed" record. Either the external system deduplicates (an idempotency key derived from the message id), or you record the intent first and check the provider's status before charging again.

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