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Answer: At-least-once delivery, Exactly-once delivery
**Correct Options: C. At-least-once delivery and A. Exactly-once delivery** **Explanation:** At-least-once delivery is a feature that ensures every message published to a topic is delivered to at least one subscriber, which is crucial for preventing message loss in scenarios involving failures or network issues. Exactly-once delivery, while more complex to implement, ensures each message is delivered exactly once, which can be beneficial for systems where message duplication is not acceptable. However, the standard guarantee provided by Pub/Sub is at-least-once delivery. **Why other options are incorrect:** - **B. Load balancing:** This technique is used to distribute traffic across servers to enhance performance and reliability, not related to message delivery guarantees. - **D. Message deduplication:** This is a process to remove duplicate messages, not a delivery guarantee feature. - **E. Both A and C:** While both features are related to message delivery, the standard guarantee provided by Pub/Sub is at-least-once delivery, with exactly-once delivery being more complex and not the default.
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In designing a real-time analytics system for a global e-commerce platform, you are tasked with selecting a messaging service that guarantees no message is lost during transmission, even in the event of system failures. The system must handle high throughput and scale dynamically with the number of transactions, which can spike during sales events. Considering these requirements, which feature of Google Cloud Pub/Sub ensures that every message is delivered to subscribers at least once, providing the reliability needed for such a critical system? Choose the best option.
A
Exactly-once delivery
B
Load balancing
C
At-least-once delivery
D
Message deduplication
E
Both A and C