[Cassandra Wiki] Update of "FAQ" by JonathanEllis

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The following page has been changed by JonathanEllis:
http://wiki.apache.org/cassandra/FAQ

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  = Frequently asked questions =
  
- If you know the/an answer, please add it. If you have additional questions, please add them. If you know an existing answer is incorrect, inaccurate or insufficient, please correct or expand it.
+ Why can't I make Cassandra listen on 0.0.0.0 (all my addresses)?
  
- == Application development ==
+ Cassandra is a gossip-based distributed system.  ListenAddress is also "contact me here address," i.e., the address it tells other nodes to reach it at.  Telling other nodes "contact me on any of my addresses" is a bad idea; if different nodes in the cluster pick different addresses for you, Bad Things happen.
  
- Developing applications which use Cassandra to store their data
+ If you don't want to manually specify an IP to ListenAddress for each node in your cluster (understandable!), leave it blank and Cassandra will use InetAddress.getLocalHost() to pick an address.  Then it's up to your sysadmin to make things resolve correctly (/etc/hosts/, dns, etc).
  
- === What is the maximum data size I can store in a column / column family / supercolumn per key? ===
+ See https://issues.apache.org/jira/browse/CASSANDRA-256 and CASSANDRA-43 for more gory details.
  
- === If I do a key range scan, what order do things come back in? What collation does it use to compare the keys? ===
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- === How can I completely delete a row ===
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- === What do I need to do to create a new table in an existing installation? ===
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- === How do I control Cassandra's voracious appetite for RAM? I don't have three machines with 2G+ each in my test environment. ===
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- == Systems administration ==
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- Operational issues involved in managing Cassandra installations
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- === How do I see how much space is being used across all nodes? ===
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- === I need to take a node down permanently, how do I tell Cassandra to redistribute data elsewhere, or don't I need to? ===
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- === I've just commissioned a new node, how do I tell Cassandra to migrate data there? ===
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- === I've got nodes with vastly differing amounts of disc capacity, how can I tell Cassandra to balance data accordingly? ===
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- === I need to migrate a node to new hardware / OS / reinstall etc, how do I do it preserving the data? ===
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- == How Cassandra works ==
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- === How are data distributed between nodes? ===
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- === What happens to new data inserts / updates if a node is offline temporarily? ===
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- === What happens if a node is "sick" but not completely dead e.g. has a hardware failure or something so it still pings, but can't do useful work? ===
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- === How do I manage Cassandra's memory usage? My machines have lots of ram but I don't want to use it all for Cassandra. ===
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- == Developing Cassandra itself ==
-