SDN Controller Programming Guide

Figure 35 Mental Model Comparison between Relational Models and Cassandra

Although this table provides a mapping of the terms, a more accurate analogy is a nested sorted

map. Cassandra stores data in the format as follows:

Map<RowKey, SortedMap<ColumnKey, ColumnValue>>

So, there is a sorted map of RowKeys to an internal Sorted map of Columns sorted by the

ColumnKey. The following figure illustrates a Casssandra row.

Figure 36 Cassandra Row

This is a simple row with columns. There are other variants like Composite Columns and Super

Columns which allow more levels of nesting. These can be visited if there is a need for these in the

design.

One important characteristic of Cassandra is that is schema-optional. This means the columns

need not be defined upfront. They can be added dynamically as and when required and further

all rows need not have the same number and type of columns.

Some important points to be noted during migration of data from RDBMS to NOSQL are as

follows:

 Model data with nested sorted maps in mind as mentioned above. This provides an efficient

and faster response time for queries.

 Model Column families around queries.

 De-normalize data as needed. Too much of de-normalization can have side effects. A right

balance needs to be struck.

Modeling Data Around Queries