Build fluency in the vocabulary of protecting a distributed lock against a stale write from a paused client.
0 / 5 completed
1 / 5
A teammate explains that every time a distributed lock is granted, the lock service issues a strictly increasing number along with it, and the resource being protected rejects any write tagged with a fencing token lower than the highest one it has already seen, so a client that was paused so long its lock actually expired can never corrupt the resource even if it wakes up and issues a stale write after a new client has already taken over the lock. What distributed-locking safety mechanism is being described?
A fencing token is a strictly increasing number issued by a lock service alongside every lock grant, and the resource being protected rejects any write tagged with a fencing token lower than the highest one it has already accepted, which matters because a distributed lock can expire out from under a client that was paused for an unexpectedly long garbage-collection pause or network delay, and without a fencing token that paused client could wake up, believe it still holds the lock, and issue a stale write that corrupts the resource even after a new client has already taken over. A DNS zone transfer is an unrelated concept about replicating name server records. This reject-writes-tagged-with-an-old-token-number approach is exactly why fencing tokens are what make a distributed lock actually safe against a paused client waking up and issuing a stale write, which a lock's expiration alone cannot prevent.
2 / 5
During a design review, the team adopts fencing token for a distributed storage system where a client holding a lock can be paused for an unpredictable amount of time by a garbage-collection pause, specifically so a write from a client whose lock has actually already expired can never be mistaken for a valid write from the current lock holder. Which capability does this provide?
Fencing token here provides protection against a stale write from a client whose lock already expired, since the storage system rejects any write carrying a fencing token lower than the highest one it has already accepted. Trusting any write from a client that believes it still holds the lock, with no fencing token to detect that the lock had actually already expired and been reassigned is the alternative this avoids. This behavior is exactly why fencing token is favored in this kind of scenario.
3 / 5
In a code review, a dev notices a distributed storage system trusts any write from a client that believes it still holds the lock, with no fencing token attached, so a client paused long enough for its lock to expire and be reassigned can wake up and corrupt the resource with a stale write that the system has no way to detect. What does this represent?
This is a missed fencing token-opportunity, since a fencing token would let the resource reject the stale write from the paused client instead of trusting it just because the client believed it still held the lock. A cache eviction policy is an unrelated concept about discarded cache entries. This pattern is exactly the kind of gap a reviewer flags once the tradeoffs are understood.
4 / 5
An incident report shows a distributed storage resource was silently corrupted because a client that had been paused by an unexpectedly long garbage-collection pause woke up still believing it held the lock, issued a write, and the system had no way to detect that a new client had already taken over the lock in the meantime. What practice would prevent this?
Requiring every lock grant to carry a fencing token and having the resource reject any write tagged with a token lower than the highest one it has already accepted, so the paused client's stale write is rejected. Continuing the prior approach regardless of the risk it has already caused is exactly what led to the incident described here. This fix is the standard remedy once the root cause is confirmed.
5 / 5
During a PR review, a teammate asks why the team reaches for fencing token instead of trusting a client's write based solely on it believing it still holds the lock. What is the reasoning?
fencing tokens trade a small amount of added bookkeeping, tracking the highest accepted token per resource, for a hard guarantee against a stale write from a paused client, while trusting a client's belief that it holds the lock is simpler but leaves the system exposed to exactly the kind of corruption a long pause can cause. This is exactly why fencing token is favored when a paused client waking up with a stale, expired lock is a real risk to data integrity, while trusting a client's write based solely on it believing it still holds the lock remains acceptable when pauses long enough to expire a lock are considered acceptably rare and the resource is not critical enough to warrant the extra bookkeeping.
What does the "Fencing Token Vocabulary" vocabulary exercise cover?
This exercise tests real IT vocabulary related to fencing token vocabulary through 5 multiple-choice questions, each built from realistic workplace sentences rather than abstract definitions.
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How many questions does this exercise have?
This exercise has 5 questions. Each one shows a real-world sentence or scenario with multiple-choice options and an explanation once you answer.
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Are these vocabulary exercises connected to other topics?
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How is this different from reading a glossary or blog article?
Exercises like this one are active recall drills — you have to choose the correct term or phrasing yourself, which builds retention faster than passively reading a definition.
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