At what point or under what conditions should message sending to the queue be initiated — before the transaction is completed or after its confirmation?

Sending a message to the queue should be initiated after confirming (commit) the transaction. This is because if the message is sent before the transaction is completed and the database transaction is rolled back, the message will already be in the queue, leading to data and message desynchronization.

The correct approach is to first successfully complete the transaction, then send the message. If a mechanism supporting atomicity is used (for example, transactions with two-phase commit support or the outbox pattern), consistency between the database and the queue can be ensured.

Example of using the outbox pattern:

1. Within the transaction, record data and the message in a special outbox table.
2. After the transaction commits, a separate process reads from the outbox and sends messages to the queue.

Thus, it is guaranteed that the message is sent only if the transaction has been successfully completed.