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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "SPOF" by SteveLoughran
Date Tue, 21 Jul 2009 11:16:42 GMT
Dear Wiki user,

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

The following page has been changed by SteveLoughran:
http://wiki.apache.org/hadoop/SPOF

The comment on the change is:
explain SPOF. 

New page:
= SPOF: Single Point of Failure =

An SPOF is a single part of a system, which, if it fails, takes down the entire system. 

In Hadoop, the NameNode is a SPOF. DNS may also be SPOF, unless you have failover. The network
may be a SPOF, depending on is redundancy, as can be the room's power supply. 

People can be SPOFs too. If only one person knows the database admin password, you can be
sure they are on vacation when the password is needed. If only one developer understands how
the mission-critical MapReduce algorithm works, they are the SPOF. 


There is always a SPOF. Even when you think you have anticipated and eliminated every SPOF,
there is one out there, waiting. How you find it? You wait.


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