Scaling Reads medium
You shard your 'Orders' database by `Order_ID`. Your Analytics team needs to run a query: `SELECT * FROM Orders WHERE Date > '2023-01-01'`. Why is this query inefficient?
- A Sharded databases do not support dates.
- B It causes a 'Scatter-Gather' operation: The query must be broadcast to *every* shard because the Shard Key (`Order_ID`) is not part of the filter (`Date`).
- C The query is too simple.
- D It will cause a deadlock.
Answer: B. It causes a 'Scatter-Gather' operation: The query must be broadcast to *every* shard because the Shard Key (`Order_ID`) is not part of the filter (`Date`).
Without the shard key, the router doesn't know where the data lives. It must ask everyone. The system is only as fast as the slowest shard (Tail Latency).
One system design question a day, with spaced repetition so the ones you miss come back.
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