[Cassandra Wiki] Update of "Operations" by JonathanEllis

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The "Operations" page has been changed by JonathanEllis.
http://wiki.apache.org/cassandra/Operations

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New page:
= Ring management =

Each Cassandra server [node] is assigned a unique Token that determines what keys it is the primary replica for.  If you sort all nodes' Tokens, the Range of keys each is responsible for is (!PreviousToken, !MyToken], that is, from the previous token (exclusive) to the node's token (inclusive).  The machine with the lowest Token gets both all keys less than that token, and all keys greater than the largest Token; this is called a "wrapping Range."

(Note that there is nothing special about being the "primary" replica, in the sense of being a point of failure.)

When the !RandomPartitioner is used, Tokens are integers from 0 to 2**127.  Keys are converted to this range by MD5 hashing for comparison with Tokens.  (Thus, keys are always convertible to Tokens, but the reverse is not always true.)

== Multiple Datacenters ==

= Adding new nodes =

Adding new nodes is called "bootstrapping."

To bootstrap a node, turn AutoBootstrap on in the configuration file, and start it.

If you explicitly specify an InitialToken in the configuration, the new node will bootstrap to that position on the ring.  Otherwise, it will pick a Token that will give it half the keys from the node with the most disk space used, that does not already have another node boostrapping into its Range.

= Moving nodes =

= Load balancing =