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

Verifying a DRBD filesystem

A fairly-common maintenance concern regarding synchronized devices is verification. The question we should always ask ourselves in a high-availability scenario is: How confident are we that the data on both nodes match?

The drbdadm utility provides a parameter specifically for addressing this need. However, there are some caveats to consider when using it, which we will explain in this recipe.

Getting ready

Follow the recipes defined in all previous sections before starting here. At the very least, we need a fully operational DRBD node pair to follow this recipe.

How to do it...

Follow these steps as the root user on pg1:

  1. Add this block of text inside the resource section defined in /etc/drbd.d/pg.res:
        net { 
          verify-alg md5; 
  1. Run this command to make DRBD reread its configuration files:
drbdadm adjust pg
  1. Begin verification with this command:
drbdadm verify pg
  1. Monitor /proc/drbd until verification is complete:
watch cat /proc/drbd...