Nick Puz created CASSANDRA-5667:
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Summary: Change timestamps used in CAS ballot proposals to be more
resilient to clock skew
Key: CASSANDRA-5667
URL: https://issues.apache.org/jira/browse/CASSANDRA-5667
Project: Cassandra
Issue Type: Bug
Components: Core
Environment: n/a
Reporter: Nick Puz
The current time is used to generate the timeuuid used for CAS ballots
proposals with the logic that if a newer proposal exists then the current one
needs to complete that and re-propose. The problem is that if a machine has
clock skew and drifts into the future it will propose with a large timestamp
(which will get accepted) but then subsequent proposals with lower (but
correct) timestamps will not be able to proceed. This will prevent CAS write
operations and also reads at serializable consistency level.
The work around is to initially propose with current time (current behavior)
but if the proposal fails due to a larger existing one re-propose (after
completing the existing if necessary) with the max of (currentTime,
mostRecent+1, proposed+1).
Since small drift is normal between different nodes in the same datacenter this
can happen even if NTP is working properly and a write hits one node and a
subsequent serialized read hits another. In the case of NTP config issues (or
OS bugs with time esp around DST) the unavailability window could be much
larger.
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