Designing Distributed Systems, 2nd Edition

Chapter 13. Coordinated Batch Processing

Chapter 12 described a number of patterns for splitting and chaining queues together to achieve more complex batch processing. Duplicating and producing multiple different outputs is often an important part of batch processing, but sometimes it is equally important to pull multiple outputs back together in order to generate some sort of aggregate output. A generic illustration of such a pattern is shown in Figure 13-1.

Figure 13-1. A generic parallel work distribution and result aggregation batch system

Probably the most canonical example of this aggregation is the reduce part of the MapReduce pattern. It’s easy to see that the map step is an example of sharding a work queue, and the reduce step is an example of coordinated processing that eventually reduces a large number of outputs down to a single aggregate response. However, there are a number of different aggregate patterns for batch processing, and this chapter discusses a number of them in addition to real-world applications.

Join (or Barrier Synchronization)

In previous chapters, we saw patterns for breaking up work and distributing it in parallel on multiple nodes. In particular, we saw how a sharded work queue could distribute work in parallel to a number of different work queue shards. However, sometimes when processing a workflow, it is necessary to have the complete set of ...