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

Deciphering database locks

It's not uncommon for various elements of the database to block each other. Queries can lock shared resources, system maintenance can temporarily prevent a transaction from committing; the list is endless. As a result, a critical aspect of troubleshooting a PostgreSQL system is tracking down blocked systems, and what might be preventing normal operation.

There are two very powerful ways to decipher locks within PostgreSQL in the pg_locks view and the new PostgreSQL 9.6 pg_blocking_pids function. Let's see why these approaches are so useful.

Getting ready

The pg_locks view needs no special access for use, and the pg_blocking_pids function can be called by any user. However, these resources are of limited utility without full access to pg_stat_activity as well. To proceed with this recipe, either connect to the database as a superuser (such as the postgres user), or refer to the Checking the pg_stat_activity view recipe to circumvent this limitation.

How to do it...