We often have clients ask about one or more of the NoSQL technologies as potential replacements for their RDBMS (typically MySQL) to simplify scaling. What I think makes much more sense with regard to these NoSQL and SQL storage systems is an AND instead of an OR discussion. Consider implementing a multi-paradigm data storage layer that provides the appropriate persistent storage system for the different types of data in your application. This approach is similar to our RFM approach to data storage. Consider questions such as how often do you need the data, how quickly do you need it, how relational is the data, etc. There are at least four benefits of this multi-paradigm approach: simpler scaling, improved application performance, easier application development, and reduced cost.
The AKF Scale Cube provides a straightforward way to scale any relational database through the three axes but we know that splitting data relationships once they’ve been established isn’t easy. It requires work and lots of coordination between teams. By limiting what gets stored relationally to only the minimum that is required means fewer splits along any axis. Many of the NoSQL technologies provide auto sharding and asynchronous replication. Re-indexing keys across another node is much simpler than migrating tables into another database.
While relational databases can have great performance, unless the table is pinned in memory or the query results are cached in memory, an in memory data store will always outperform SQL. In many applications we could make use of in memory solutions like Memcache or MongoDB to improve performance of retrieving high value data.
As Debasish Ghosh states in his article Multiparadigm Data Storage for Enterprise Applications, storing data the way it is used in an application, simplifies programming and makes it easier to decentralize data processing. If the application treats the data as a document why break it apart to store it relationally when we have viable document storage engines. Storing the data in a more native format allows for quicker development.
For data that’s not needed often, cache it in other places (such as a CDN) or lazy load it from a low cost storage tier such as Amazon’s S3. This might work well for applications hosted in the cloud. The benefit of this a lower cost per byte stored, especially when considering all costs including administrators for the more complex data storage systems such as relational databases.
A final step in implementing a multi-paradigm data storage layer is an asynchronous message queue for data that needs to move up and down the stack. Implementing ActiveMQ or RabbitMQ to asynchronously move data from one layer to another as needed relieves the application of this burden. As an example consider an application that routes picking baskets for inventory in a warehouse. This is typically thought of as a graph with bins of inventory as nodes and the aisles as edges. For faster retrieval you could store this in a graph database such as Neo4J for ease of development and performance reasons. You could then asynchronously persist these maps in a MySQL database for reporting and older versions into an S3 bucket for historic archiving. This combination provides faster performance, easier development, simpler scaling, and reduced cost.
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