Chapter 7
Modifying Data Stores and Managing Evolution
WHAT’S IN THIS CHAPTER?
- Managing data schema in document databases, column-oriented stores, and key/value databases
- Maintaining data stores as the attributes of a data set evolves
- Importing and exporting data
Over time, data evolves and changes; sometimes drastically and other times at a slower pace and in less radical ways. In addition, data often outlives a single application. Probably designed and structured with a specific use case in mind, data often gets consumed in ways never thought of originally.
The world of relational databases, however, doesn’t normally pay much heed to the evolution of data. It does provide ways to alter schema definitions and data types but presumes that, for the most part, the metadata remains static. It also assumes uniformity of structure is common across most types of data sets and believes in getting the schema right up front. Relational databases focus on effective storage of structured and dense data sets where normalization of data records is important.
Although the debate in this chapter isn’t whether RDBMS can adapt to change, it’s worth noting that modifying schemas and data types and merging data from two versions of a schema in an RDBMS is generally complex and involves many workarounds. For example, something as benign as adding a new column to an existing table (that has some data) could pose serious issues, especially if the new column needs to have unique values. Workarounds ...
