Jie Yu created MESOS-1038:
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Summary: Log coordinator should demote itself after a write is
discarded.
Key: MESOS-1038
URL: https://issues.apache.org/jira/browse/MESOS-1038
Project: Mesos
Issue Type: Bug
Affects Versions: 0.17.0
Reporter: Jie Yu
Fix For: 0.18.0
After a write operation (append/truncate) is discarded (e.g. due to timeout),
the log coordinator should demoted itself, because it does not know if the
previous write operation has been agreed or not. It needs to get re-elected to
be able to write again.
Consider the following case: there are 3 replicas R1, R2 and R3, and C1 is the
coordinator co-located with R1. Say C1 tries to write at position 1. All
replicas receive the write request and accept the write request. C1
successfully collects a quorum of OK responses, and right before it sends out
the learned message, the write operation is discarded.
The value at position 1 has been agreed, however, if we don't demote C1 after
the write operation is discarded, C1 will try to write to the same position
(position 1) again, with possibly a different value. And that value can be
later agreed by all replicas, leading to an inconsistency.
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