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From Apache Wiki <>
Subject [Cassandra Wiki] Update of "FAQ" by JonathanEllis
Date Thu, 22 Apr 2010 20:11:35 GMT
Dear Wiki user,

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The "FAQ" page has been changed by JonathanEllis.
The comment on this change is: add How can I iterate over all the rows in a ColumnFamily?.


   * [[#change_replication|Can I change the ReplicationFactor on a live cluster?]]
   * [[#large_file_and_blob_storage|Can I store large files or BLOBs in Cassandra?]]
   * [[#jmx_localhost_refused|Nodetool says "Connection refused to host:", for any
remote host. What gives?]]
+  * [[#iter_world|How can I iterate over all the rows in a ColumnFamily?]]
   * [[#no_keyspaces|Why were none of the keyspaces described in cassandra.xml loaded?]]
@@ -219, +220 @@

  If you are not using DNS, then make sure that your `/etc/hosts` files are accurate on both
ends. If that fails try passing the `-Djava.rmi.server.hostname=$IP` option to the JVM at
startup (where `$IP` is the address of the interface you can reach from the remote machine).
+ <<Anchor(iter_world)>>
+ == How can I iterate over all the rows in a ColumnFamily? ==
+ Simple but slow: Use get_range_slices, start with the empty string, and after each call
use the last key read as the start key in the next iteration.
+ Better: use HadoopSupport.
  == Why were none of the keyspaces described in cassandra.xml loaded? ==
  Prior to 0.7, cassandra loaded a set of static keyspaces defined in cassandra.xml (previously
storage-conf.xml).  [[|CASSANDRA-44]] added
the ability to modify schema dynamically on a live cluster.  Part of this change required
that we ignore the schema defined in cassandra.xml.  The upshot is that you need to define
the schema yourself.  There are currently two ways to do this.  First, in 0.7 there is a `loadSchemaFromXML`
method defined in `StorageServiceMBean` that will load the schema defined in storage-conf.xml.
 This is a one-time operation.  A node that has had its schema defined via `loadSchemaFromXML`
will load its schema from the system table on subsequent restarts.  Second, you can modify
the schema on a node using the `system_*` thrift operations (see [[API|API]]).

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