Book Image

PostgreSQL 9 High Availability Cookbook

By : Shaun Thomas
Book Image

PostgreSQL 9 High Availability Cookbook

By: Shaun Thomas

Overview of this book

A comprehensive series of dependable recipes to design, build, and implement a PostgreSQL server architecture free of common pitfalls that can operate for years to come. Each chapter is packed with instructions and examples to simplify even highly complex database operations. If you are a PostgreSQL DBA working on Linux systems who want a database that never gives up, this book is for you. If you've ever experienced a database outage, restored from a backup, spent hours trying to repair a malfunctioning cluster, or simply want to guarantee system stability, this book is definitely for you.
Table of Contents (12 chapters)
11
Index

Using LVM snapshots

One of the reasons we created a second layer of LVM on top of DRBD was to provide filesystem snapshot capabilities. When we create a snapshot, all files on a particular volume will appear static on that snapshot until one of the following two things happens:

  • We destroy the snapshot
  • The amount of changes on the source volume is larger than the space we reserved for the snapshot

This is the primary reason we left 5 percent space unused within our PostgreSQL volume group. If we create a snapshot, up to 5 percent of the database can change before we have to remove it. For larger storage devices, this should give us a lot of time to perform emergency restores, create byte-stable backups, or any other operation that requires consistent data.

In this recipe, we'll learn how to properly allocate, use, and remove an LVM snapshot.

Getting ready

For this recipe, we want a formatted and active XFS filesystem. Please follow the recipe in Formatting an XFS filesystem before continuing...