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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "ZooKeeper/FailureScenarios" by jeremyhanna
Date Thu, 09 Dec 2010 21:24:22 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.

The "ZooKeeper/FailureScenarios" page has been changed by jeremyhanna.
The comment on this change is: Adding the page content for how zookeeper handles specific
failure scenarios..
http://wiki.apache.org/hadoop/ZooKeeper/FailureScenarios

--------------------------------------------------

New page:
= How ZooKeeper Handles Failure Scenarios =

=== Network partitions ===

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.

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