Unbundled versus integrated systems
If unbundling does indeed become the way of the future, it will not replace databases in their current form—they will still be needed as much as ever. Databases are still required for maintaining state in stream processors, and in order to serve queries for the output of batch and stream processors (see “The Output of Batch Workflows” on page 411 and “Processing Streams” on page 464). Specialized query engines will continue to be important for particular workloads: for example, query engines in MPP data warehouses are optimized for exploratory analytic queries and handle this kind of workload very well (see “Comparing Hadoop to Distributed Databases” on page 414).
The complexity of running several different pieces of infrastructure can be a problem: each piece of software has a learning curve, configuration issues, and operational quirks, and so it is worth deploying as few moving parts as possible. A single integrated software product may also be able to achieve better and more predictable performance on the kinds of workloads for which it is designed, compared to a system consisting of several tools that you have composed with application code . As I said in the Preface, building for scale that you don’t need is wasted effort and may lock you into an inflexible design. In effect, it is a form of premature optimization.
The goal of unbundling is not to compete with individual databases on performance for particular workloads; the goal is to allow you to combine several different databases in order to achieve good performance for a much wider range of workloads than is possible with a single piece of software. It’s about breadth, not depth—in the same vein as the diversity of storage and processing models that we discussed in “Comparing Hadoop to Distributed Databases” on page 414.
Thus, if there is a single technology that does everything you need, you’re most likely best off simply using that product rather than trying to reimplement it yourself from lower-level components. The advantages of unbundling and composition only come into the picture when there is no single piece of software that satisfies all your requirements.