fencing token
A mechanism used in distributed locks. Each time the lock service grants a lock, it returns a monotonically increasing token that the client carries when accessing downstream resources. Downstream resources accept only requests whose token is no less than the maximum token already seen, thereby blocking stale writes from previous holders.
Timeline (last 90 days)
The fencing token originates from a classic distributed lock paper; the core idea is that the lock service returns a monotonically increasing token each time it grants the lock, the client carries this token when accessing downstream resources, and downstream resources only accept requests whose token is no less than the maximum value seen, thereby cutting off stale writes.
In the LangGraph scenario, the fencing token is usually implemented as a lease_epoch or version column in the lease table, atomically incremented on each ownership transfer, and the checkpoint write statement takes the form UPDATE checkpoints SET ... WHERE thread_id = ? AND lease_epoch = ?; if the affected row count is zero, ownership has been lost and the worker should immediately abort the current task.
A more robust design requires multiple safeguards: lease + fencing token + checkpoint version + idempotent writes, along with monitoring lease renewal latency and issuing advance alerts for Workers nearing expiration; when a Worker's state cannot be determined, it is better to conservatively wait longer than to take over rashly.
All Facts (3)
The fencing token originates from a classic distributed lock paper; the core idea is that the lock service returns a monotonically increasing token each time it grants the lock, the client carries this token when accessing downstream resources, and downstream resources only accept requests whose token is no less than the maximum value seen, thereby cutting off stale writes.
50%UnverifiedIn the LangGraph scenario, the fencing token is usually implemented as a lease_epoch or version column in the lease table, atomically incremented on each ownership transfer, and the checkpoint write statement takes the form UPDATE checkpoints SET ... WHERE thread_id = ? AND lease_epoch = ?; if the affected row count is zero, ownership has been lost and the worker should immediately abort the current task.
50%UnverifiedA more robust design requires multiple safeguards: lease + fencing token + checkpoint version + idempotent writes, along with monitoring lease renewal latency and issuing advance alerts for Workers nearing expiration; when a Worker's state cannot be determined, it is better to conservatively wait longer than to take over rashly.
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