In this section, we will delve into the details of how various open source software projects use Apache ZooKeeper to implement some of their functionality. As it's beyond the scope of this book to give a full functional description of the individual projects, readers are advised to go through the respective project pages to learn more about their design and architectural details.
The Apache BookKeeper (http://zookeeper.apache.org/bookkeeper/) is a subproject of ZooKeeper. BookKeeper is a highly available and reliable distributed logging service. Hedwig is a topic-based distributed publish/subscribe system built on BookKeeper. In this section, we will take a sneak peek of Apache BookKeeper.
BookKeeper can be used to reliably log streams of records. It achieves high availability through replication. Applications that need to log operations or transactions in a reliable fashion so that crash recovery can be done in case of failure can use BookKeeper...