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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "ZooKeeper/PaxosRun" by FlavioJunqueira
Date Fri, 11 Dec 2009 08:11:23 GMT
Dear Wiki user,

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

The "ZooKeeper/PaxosRun" page has been changed by FlavioJunqueira.
http://wiki.apache.org/hadoop/ZooKeeper/PaxosRun?action=diff&rev1=6&rev2=7

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  In this page, we show an example of a Paxos run that violates the primary order of messages.
The basic idea is that if we have three proposers over time and three acceptors, we can have
a situation in which a proposer proposes A and B, but only B is committed. For ZooKeeper,
operations are state changes, and such cases can lead to an inconsistent state. In this particular
example, the state change B depends upon A, but A was not committed.
  
- Note that we concentrate on instances 27, 28, and 29, for the sake of illustration. We have
omitted common optimizations like sending one 1a message for all instances or summarizing
1b messages. We also only show the values accepted along with their ballots as part of the
state of an acceptor.   
+ Note that we concentrate on instances 27, 28, and 29, for the sake of illustration. For
simplicity of presentation, we assume in each figure that the single proposer is the leader
for the corresponding part of the execution. We omit common optimizations like sending one
1a message for all instances or summarizing 1b messages. We also only show the values accepted
along with their ballots as part of the state of an acceptor.   
  
  '''Notation''': For the following figures, we use '''''bold italics''''' to represent the
state of an acceptor, and regular font to represent messages.
  

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