Scaling Writes hard
A client acquires a distributed lock (e.g., in ZooKeeper), pauses for a long GC, loses the lock, and then wakes up to write. How do 'Fencing Tokens' prevent data corruption?
- A They kill the client.
- B They use GPS clocks.
- C They encrypt the data.
- D The storage layer checks the token (epoch). If the token in the write request is lower than the highest token seen so far, the write is rejected.
Answer: D. The storage layer checks the token (epoch). If the token in the write request is lower than the highest token seen so far, the write is rejected.
Fencing pushes the enforcement to the storage. Even if a 'zombie' client thinks it holds the lock, the database sees it has an old epoch number and rejects the modification.
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