Introduction

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Overview

High Availability, as a term bandied about among database administrators, has been around for many years and can be used in all kinds of situations to describe nearly anything that involves keeping your business up and running, every minute of every day. But High Availability (HA) as a generally recognizable set of technologies and practices has undergone a radical transformation over the past few years. Gone may be the dot com buzz and the e-business hype, but a lasting legacy remains from the salad days of the fin de siecle: your systems should be available 24 hours a day, 7 days a week.

The parameters surrounding this simple principle are wide and complex, but the reality is simple: availability is defined, ultimately, by end users of your systems who have no notion of what HA requires, but simply want to buy books at midnight, or check their 401(k) over the weekend, or run financial intelligence reports at the end of every month. What that means is that any true availability solution must encompass the entire technology stack, from the database to the application server to the network. This requires the cooperation of nearly every aspect of a company's technology staff.

Gone, of course, are the oversized budgets to make availability happen at any cost, and technology providers and solution peddlers have gone out of their way to offer the modern DBA and the modern System Administrator affordable options in the epic battle against the enemies of uptime: hardware failure, database corruption, user error, even natural disasters. Most of these modern solutions usually come in the form of proprietary hardware configurations or costly software add-ons to systems you already have in place. And, honestly, most of them are pitched to a System Administrator audience. But High Availability for the database remains a problem best tackled by the database administrator, who is ultimately responsible for the well-being of the data.

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