Adding NoSQL Persistence to Storm - Real-time Analytics with Storm and Cassandra - page 121

The live updates are being recorded under the StatusUpdates table that has
the username , message , and update_id (which is actually a UUID) prop-
erty.
While designing a Cassandra column family, you should make extensive use of
the functionality provided by UUIDs, which can be employed for sequencing
data.
The combination of the user_id and update_id properties from timeser-
iesTable can uniquely identify a row in chronology.
Cassandra makes use of the first column defined in the primary key as the parti-
tion key; this is also known as the row key.
• Expiring columns : These are special types of Cassandra columns that have a
time to live ( TTL ) associated with them; the values stored in these columns are
automatically deleted or erased after the TTL has elapsed. These columns are
used for use cases where we don't want to retain data older than a stated interval;
for instance, if we don't need data older than 24 hours. In our column family, I
would associate a TTL of 24 hours with every column that is being inserted, and
this data will be automatically deleted by Cassandra after 24 hours of its insertion.
• Counter columns : These are again specialized function columns that store a
number incrementally. They have a special implementation and a specialized us-
age for situations where we use counters; for instance, if I need to count the num-
ber of occurrences of an event.