Appendix A. Exploring the HBase system
Over the course of the book, you’ve learned a bit of theory about how HBase is designed and how it distributes the load across different servers. Let’s poke around the system a little and get familiar with how these things work in practice. First, we’ll look at what ZooKeeper says about your HBase instance. When running HBase in standalone mode, ZooKeeper runs in the same JVM as the HBase Master. In chapter 9, you learned about fully distributed deployments, where ZooKeeper runs as a separate service. For now, let’s examine the commands and see what ZooKeeper has to tell you about your deployment.
Your main interface to interact directly with ZooKeeper is through the HBase shell. Launch the shell, and issue the zk_dump command.
Let’s look at a zk_dump from a fully distributed HBase instance. We’ve included the output from a running cluster and masked the server names. The portions in bold are analogous to the things we mentioned: