Scaling Reads medium
In a DynamoDB/Cassandra sharded system, why are Global Secondary Indexes often 'Eventually Consistent'?
- A Because they are stored on the same machine.
- B Updating the GSI might require a network hop to a *different* shard than the main item. Using strong consistency would require a slow distributed transaction (2PC).
- C They are read-only.
- D They use UDP.
Answer: B. Updating the GSI might require a network hop to a *different* shard than the main item. Using strong consistency would require a slow distributed transaction (2PC).
To keep writes fast, the system writes the main item and returns 'Success', then updates the remote index asynchronously.
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