Where would you typically apply strong consistency in a domain?

Where would you typically apply strong consistency in a domain?

• A. Bank balances, stock order books.
• B. Social media feed.
• C. CDN cache.
• D. Email delivery.

Answer: (A)

Strong consistency means that after a write completes, all subsequent reads reflect that exact update. This is essential when correctness depends on the most current state being visible everywhere, such as financial state and order sequencing. In bank balances and stock order books, the integrity of the system hinges on exact values and correct ordering. If a transfer happens, everyone must see the updated balance immediately, and trades in an order book must reflect the true, current state to prevent double-spending, incorrect holdings, or unfair trade matching. Any read that returns an older value could lead to incorrect balances or mispriced trades, causing financial loss and trust issues. Other domains tolerate some delay or inconsistency. A social media feed often accepts eventual consistency, since users care about timely content but can tolerate a momentary mismatch in what they see versus other users. A CDN cache serves content quickly by delivering cached data, which inherently accepts staleness for performance. Email delivery is typically asynchronous and long-running, where reliability and eventual delivery are prioritized over instantaneous consistency. So, the domain where strong consistency is most critical and appropriate is the one dealing with precise financial figures and ordered transactions.

Strong consistency means that after a write completes, all subsequent reads reflect that exact update. This is essential when correctness depends on the most current state being visible everywhere, such as financial state and order sequencing.

In bank balances and stock order books, the integrity of the system hinges on exact values and correct ordering. If a transfer happens, everyone must see the updated balance immediately, and trades in an order book must reflect the true, current state to prevent double-spending, incorrect holdings, or unfair trade matching. Any read that returns an older value could lead to incorrect balances or mispriced trades, causing financial loss and trust issues.

Other domains tolerate some delay or inconsistency. A social media feed often accepts eventual consistency, since users care about timely content but can tolerate a momentary mismatch in what they see versus other users. A CDN cache serves content quickly by delivering cached data, which inherently accepts staleness for performance. Email delivery is typically asynchronous and long-running, where reliability and eventual delivery are prioritized over instantaneous consistency.

So, the domain where strong consistency is most critical and appropriate is the one dealing with precise financial figures and ordered transactions.