Databases Reference
In-Depth Information
3.
Planning for Concurrent Writes:
In Cassandra, every row
within a column family is identified by the unique row key
(generally a string of unlimited length). Unlike the traditional
RDBMS primary key (which enforces uniqueness), Cassandra
doesn't impose uniqueness (duplicate row key insertion
might disturb the existing column structure). So care must be
taken to create the rows with unique row keys. Some of the
ways for creating unique row keys are as follows:
•
Surrogate/ UUID type of row keys
•
Natural row keys
Schema Migration Approach (Using ETL)
There are various ways of migrating data from relational data structures to Cassandra
structures, but if there are complex transformations and business rules involved it is
always advisable to leverage a data processing layer comprising ETL utilities (Figure
6-23
).
Figure 6-23.
Schema migration using ETL tools
By using in-built data loaders the processed data can be extracted to flat files (in
JSON format) and then uploaded to the Cassandra data structure's using these loaders.
Custom loaders could be fabricated in case of additional dispensation rules, which could
either deal the data from the processed store or the JSON files.
