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

Correcting a DRBD split brain

One looming danger when running any replication system is that of node status conflicts. This happens when more than one node has been primary, and we want to reestablish the previous mirror state. This can happen in many ways, but a common scenario can occur if the existing primary node experiences a sudden failure and the remaining secondary node is promoted to primary status.

Where we repair the old primary node, we can't simply reattach it to the DRBD network and expect successful synchronization. In cases where the last status for each node is that of a primary, DRBD will not resolve this conflict automatically. It is our job to manually choose the best primary node from our available choices, and reattach the other node.

In this recipe, we'll explore the steps necessary to reattach a malfunctioning node to an existing DRBD architecture. We can't have a highly available PostgreSQL cluster with only one functional node.

Getting ready

Since we're working with...