Creating Column Families

A Cassandra Column Family is similar to a table in a relational database management system. However, unlike relational tables, Column Families only define metadata of the columns as described below when creating a Column Family. The actual columns in a row are defined typically by the client application. The actual columns of each row can vary from each other depending on the data stored in a row.

Follow the steps below to add column families to an existing keyspace. Also see, Creating Keyspaces.

1. Click List under Cassandra Keyspaces and select a keyspace to add column families to.
   

2. Click Add a New Column Family to open the New Column Family window where you can enter column family details to the keyspace.
   
   The fields of the new column family window are described below:

   Fields	Description
   Name*	Column Family (CF) Name is mandatory. Must not contain the character "-".
   Comment	Description of the column family. Used to attach additional human-readable information about the column family to its definition
   Column Type	Standard - Super -
   Comparator	Datatype.
   Key Cache Size	Specifies the number of keys per ssTable whose locations in memory are kept in "mostly LRU" order (Only the key locations; not any column values). Specify a fraction (value less than 1) or an absolute number of keys to cache. Defaults to 200000 keys.
   Row Cache Size	Specifies the number of rows whose entire content is cached in memory. Not recommended to be used on Column Families with large rows or high write:read ratio. Specify a fraction (value less than 1) or an absolute number of rows to cache. The default is 0 meaning row caching is OFF by default.
   Row Cache Save Period In Seconds	Number of seconds between saving row caches. The row caches can be saved periodically. If one exists on start-up, it will be loaded.
   Garbage Collection Grace In Seconds	Specifies the time to wait before garbage collecting tombstones (deletion markers). Defaults to 864000 (10 days). Refer to http://wiki.apache.org/cassandra/DistributedDeletes.
   Minimum Compaction Threshold	The minimum number of SSTables needed to start a minor compaction. Increasing this value causes minor compactions to start less frequently and be more intensive. Setting this to 0 disables minor compactions. The default value is 4.
   Maximum Compaction Threshold	Specifies the maximum number of SSTables allowed before a minor compaction is forced. Decreasing this value causes minor compactions to start more frequently and be less intensive. Setting this to 0 disables minor compactions. The default value is 32.
   Default Validation Class	Default validator for row keys and column data

3. Click Save after adding column family details. The Keyspace Information window opens with links to column family operations such as share with user roles, edit or delete.
   

4. Click on the Column Family's name and then the Add New Column link to create a column.
   

   Field	Description
   Name	Name of the new column
   Index Name
   Validation Class