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

Bulletproofing with synchronous replication

Sometimes, in order to provide acceptable data durability, a high availability configuration must utilize synchronous commits. Beginning with PostgreSQL 9.1, database servers can now refuse to commit a transaction until the data is located on at least one alternate server. Unlike asynchronous replication where this is optional, synchronous replicas enforce this requirement to a fault.

Discussions in the PostgreSQL mailing list suggest that there is a long-standing misconception that synchronous replication is similar to RAID-1 operation. In RAID-1, the same exact data exists on two disks (or two disk sets), and if one of the pair fails, it continues to operate in degraded mode until the problem is addressed. This is absolutely not the case with PostgreSQL synchronous replication.

Unlike a RAID-1, PostgreSQL replicas can exist on different servers, on different networks, or even in different countries. PostgreSQL synchronous replication is a guarantee...