Book Image

PostgreSQL High Availability Cookbook - Second Edition

By : Shaun Thomas
Book Image

PostgreSQL High Availability Cookbook - Second Edition

By: Shaun Thomas

Overview of this book

Databases are nothing without the data they store. In the event of a failure - catastrophic or otherwise - immediate recovery is essential. By carefully combining multiple servers, it’s even possible to hide the fact a failure occurred at all. From hardware selection to software stacks and horizontal scalability, this book will help you build a versatile PostgreSQL cluster that will survive crashes, resist data corruption, and grow smoothly with customer demand. It all begins with hardware selection for the skeleton of an efficient PostgreSQL database cluster. Then it’s on to preventing downtime as well as troubleshooting some real life problems that administrators commonly face. Next, we add database monitoring to the stack, using collectd, Nagios, and Graphite. And no stack is complete without replication using multiple internal and external tools, including the newly released pglogical extension. Pacemaker or Raft consensus tools are the final piece to grant the cluster the ability to heal itself. We even round off by tackling the complex problem of data scalability. This book exploits many new features introduced in PostgreSQL 9.6 to make the database more efficient and adaptive, and most importantly, keep it running.
Table of Contents (18 chapters)
Title Page
About the Author
About the Reviewer
Customer Feedback

Cloning a database with walctl

One of the utilities that walctl includes is a script dedicated to creating a copy of the source database. Why don't we just use pg_basebackup? When dealing with large databases common to high availability systems, we want to copy as little data as possible. The pg_basebackup utility is a great basic tool, but it always copies every file. The walctl_clone program that we use in this recipe relies on rsync.

Of course, this raises another question: Why not just use rsync directly? Due to its extensive capabilities, rsync is inherently dangerous. Did you accidentally transpose the source and target destination parameters? If you did so, you've just erased or corrupted your database master. The walctl_clone tool wraps rsync in such a way that it can only retrieve data from a master node. We can stay safe by limiting its use to clone servers.

In this recipe, we'll introduce and invoke the walctl_clone command, which does a few other useful things on our behalf. Not...