System Design Fundamentals

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System Design Trade-offs in Interviews

When it comes to system design (especially in interviews), understanding CAP isn’t just theoretical – it guides real decisions. Interviewers often present scenarios where you need to decide between consistency and availability. Here’s how to think about it:

1. Understand the requirements of the scenario

Ask yourself: is it worse for this system to show incorrect/out-of-date data, or to not respond at all? The answer will hint at consistency vs availability

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Sharath P

Sharath P

· 8 months ago

CP scenario (Consistency + Partition)

A financial ledger system that processes inter-bank transfers requires strict correctness even if the network splits. During a partition, the system must reject writes rather than risk divergent account balances. Reads must always return the most recent committed state from a majority quorum. After the partition heals, no reconciliation steps requiring human intervention should ever be needed because the system never allowed conflicting writes.

AP scenario (Availability + Partition)

A global social network feed service must keep accepting posts, likes, and profile updates even if regions lose connectivity. During a partition, all nodes must allow local writes using last-write-wins timestamps. Clients must always get a response, preferably