Design innovative, scalable, and highly available cloud database solutions →hardMultiple ChoiceObjective-mapped
PCDE Practice Question: Design innovative, scalable, and highly available cloud database solutions
You are designing a Bigtable schema for a time-series application that records sensor readings every second. Queries always filter by device ID and time range. To avoid hotspotting and ensure recent data is retrieved quickly, which row key design is MOST effective?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Row key: (hash(deviceID)#deviceID#reverseTimestamp)
Salting (hash prefix) distributes writes across nodes, avoiding hotspots from sequential timestamps. Field promotion (device ID first) allows efficient prefix scans. Reverse timestamp ensures most recent data appears first when scanning.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Row key: deviceID#timestamp
Why it's wrong here
Without salting, sequential timestamps cause hotspotting under high write load.
- ✗
Row key: (reverseTimestamp#deviceID)
Why it's wrong here
Reverse timestamp first still causes hotspotting because all writes have similar timestamps.
- ✓
Row key: (hash(deviceID)#deviceID#reverseTimestamp)
Why this is correct
Salting distributes writes, deviceID enables filtering, reverseTimestamp orders recent first.
- ✗
Row key: timestamp#deviceID
Why it's wrong here
Timestamp first causes all writes to go to a single node, creating a hotspot.
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