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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "ZooKeeper/ProjectDescription" by PatrickHunt
Date Wed, 16 Jul 2008 18:35:45 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 PatrickHunt:
http://wiki.apache.org/hadoop/ZooKeeper/ProjectDescription

------------------------------------------------------------------------------
  
  The main differences between ZooKeeper and standard file systems are that every znode can
have data associated with it (every file can also be a directory and visa versa) and znodes
are limited to the amount of data that they can have. ZooKeeper was designed to store coordination
data: status information, configuration, location information, etc. This kind of meta-information
is usually measured in kilobytes, if not bytes. ZooKeeper has a builtin sanity check of 1M,
to prevent it from being used as a large data store, but in general it is used to store much
smaller pieces of data.
  
- service.png
+ attachment:service.png
  
  
  The service itself is replicated over a set of machines that comprise the service. These
machines maintain an in-memory image of the data tree along with a transaction logs and snapshots
in a persistent store. Because the data is kept in-memory ZooKeeper is able to get very high
throughput and low latency numbers. The downside to an in memory database is that the size
of the database that ZooKeeper can manage is limited by memory. This limitation is further
reason to keep the amount of data stored in znodes small.

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