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PCDE Practice Question: Design innovative, scalable, and highly available cloud database solutions
You are designing a Spanner schema for a global inventory system. The table Products has primary key (ProductId STRING). The table Inventory has primary key (ProductId STRING, WarehouseId INT64) and is interleaved in Products. You expect high write throughput on Inventory. Which TWO design choices will help avoid hotspots?
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
✓
Use UUID for ProductId
To avoid hotspots in Spanner, avoid monotonically increasing keys. ProductId should be a UUID or hash. Also, using a hash prefix on ProductId as the first part of the key can help distribute writes. Interleaving is fine. Secondary indexes with STORING are for reads. Reverse timestamps are for Bigtable. The correct choices are using UUID and adding a hash prefix.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use UUID for ProductId
Why this is correct
UUIDs are random and help distribute writes.
- ✓
Use a hash prefix of ProductId as the first key part in Inventory
Why this is correct
Hash prefix distributes writes across tablets.
- ✗
Reverse the timestamp in the row key
Why it's wrong here
Reversing timestamp is a Bigtable technique, not applicable to Spanner.
- ✗
Use a monotonically increasing sequence for ProductId
Why it's wrong here
Monotonically increasing keys cause hotspots.
- ✗
Create a secondary index on WarehouseId with STORING
Why it's wrong here
Secondary indexes do not affect write distribution of the primary table.
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