Explain the logic behind the occurrence of duplicates — the mechanics of the process, where exactly the problem arose during event processing?

Duplicates during event processing occur because the same event can be received and processed multiple times. This happens if the system does not guarantee idempotency or does not track already processed events.

Mechanics of the problem:

• The event is sent multiple times (for example, due to network failures or retries).
• The handler does not check whether this event has already been processed.
• As a result, duplicate records or actions are created.

The problem usually occurs at the stage of receiving and processing events when there is no mechanism for unique identification or state control. To avoid duplicates, unique event identifiers are used and checked before processing, or idempotent operations are applied.