Mastering Apache Pulsar

Chapter 2. Event Streams and Event Brokers

Event streams and event brokers are at the heart of every real-time system. An event stream is an endless series of events. Let’s revisit the banking example in Chapter 1. A borrower’s financial transactions can be considered an event stream. Each time a borrower uses their credit card, applies for a new line of credit, or deposits a check, those actions or events are appended to their event stream. Since the event stream is infinite, the bank can use it to return to any point in the borrower’s past. If the bank wanted to know what a borrower’s bank account looked like on a specific day in history, it could reconstruct that from an event stream. The event stream is a powerful concept, and when equipped with this data, it can empower organizations and developers to make life-changing experiences.

Event brokers are the technology platforms that store event streams and interact with clients that read data from or write data to event streams. Apache Pulsar is an event broker at heart. However, calling Pulsar only an event broker would minimize its scope and impact. To fully understand what makes Pulsar unique, it is beneficial to dive into some of the strengths and weaknesses of event brokers and their approaches to implementing event streams. This chapter will walk through some historical context and motivate a discussion around the need for Apache Pulsar.

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