Database Reference
In-Depth Information
Super C
r Collumn
A super column is a column whose value is not a string, but instead a named list of other
columns, which in this context are called subcolumns. The subcolumns are ordered, and the
number of columns you can define is unbounded. Super columns also differ from regular
columns in that they do not have an associated timestamp.
Super columns are not recursive; that is, they go only one level deep. A super column can
hold a map only of other columns, and not a map of more super columns.
They are defined in SuperColumn.java, which implements both the
IColumn
and
IColum-
nContainer
interfaces. The interface allows you to perform a variety of operations, includ-
ing the following: get all of the subcolumns in a super column, get a single subcolumn by
name, add a subcolumn, remove a subcolumn, check the number of subcolumns in the super
column, and check when a subcolumn was last modified.
super columns were one of the updates added by Facebook to the original data model of
Google's Bigtable.
See also
Column Family
.
Thriiftt
Thrift is the name of the RPC client used to communicate with the Cassandra server. It stat-
ically generates an interface for serialization in a variety of languages, including C++, Java,
Python, PHP, Ruby, Erlang, Perl, Haskell, C#, Cocoa, Smalltalk, and OCaml. It is this mech-
anism that allows you to interact with Cassandra from any of these client languages.
It was created in April 2007 at Facebook and donated to Apache as an incubator project in
May 2008. At the time of this writing, the Thrift interface is most likely being replaced by
the newer and more active Apache project Avro. Another advantage of Avro is that it does
not require static code generation.
You can read more about Thrift on its project page at
http://incubator.apache.org/thrift
.
Tiimesttamp
In Cassandra, timestamps for column values are supplied by the client, so it is important to
synchronize client clocks. The timestamp is by convention the number of microseconds since
the Unix epoch (midnight, January 1, 1970).
Token
Each node in the node ring has a single token that is used to claim a range of keys, based on
the value of the token in the previous node in the ring. You can specify your own token or let
