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The "ZooKeeper/FailureScenarios" page has been changed by jeremyhanna. The comment on this change is: Clarified failure scenario based on info from Henry R.. http://wiki.apache.org/hadoop/ZooKeeper/FailureScenarios?action=diff&rev1=1&rev2=2 -------------------------------------------------- When there is a network partition that separates members of the !ZooKeeper ensemble and there exists a quorum side and a non-quorum side of the partition: * if the leader is in the quorum side of the partition, all read and write requests to the quorum side continue normally. On the non-quorum side of the partition, there is no leader, so requests to read or write to those leaderless !ZooKeeper servers result in an [[ZooKeeper/ErrorHandling| error]]. - * if the leader is in the non-quorum side of the partition, that side of the partition will recognize that it no longer has a quorum of the ensemble. The leader will be demoted to being a regular !ZooKeeper server and those nodes will no longer accept reads or writes. On the quorum-side of the partition, the nodes will recognize that there is not a leader among them and will elect a new leader. When the partition is resolved, the non-quorum side will join the quorum side and update their data. + * if the leader is in the non-quorum side of the partition, that side of the partition will recognize that it no longer has a quorum of the ensemble. For writes, you need a quorum in order to commit a change so all writes will fail. For reads, there may be a narrow window where reads are returned with stale data - note that no consistency guarantees are violated here because it's legal to serve a stale value as long as you yourself haven't overwritten it. On the quorum-side of the partition, the nodes will recognize that there is not a leader among them and will elect a new leader. When the partition is resolved, the non-quorum side will join the quorum side and update their data.
