Book Image

Mastering Oracle Scheduler in Oracle 11g Databases

By : Ronald Rood
Book Image

Mastering Oracle Scheduler in Oracle 11g Databases

By: Ronald Rood

Overview of this book

Scheduler (DBMS_SCHEDULER) is included in Oracle Database and is a tool for the automation, management, and control of jobs. It enables users to schedule jobs running inside the database such as PL/SQL procedures or PL/SQL blocks, as well as jobs running outside the database like shell scripts. Scheduler ensures that jobs are run on time, automates business processes, and optimizes the use of available resources. You just need to specify a fixed date and time and Scheduler will do the rest. What if you don't know the precise time to execute your job? Nothing to worry about, you can specify an event upon which you want your job to be done and Scheduler will execute your job at the appropriate time. Although scheduling sounds quite easy, it requires programming skills and knowledge to set up such a powerful, intelligent scheduler for your project. This book is your practical guide to DBMS_SCHEDULER for setting up platform-independent schedules that automate the execution of time-based or event-based job processes. It will show you how to automate business processes, and help you manage and monitor those jobs efficiently and effectively. It explains how Scheduler can be used to achieve the tasks you need to make happen in the real world. With a little understanding of how the Scheduler can be used and what kind of control it gives, you will be able to recognize the real power that many known enterprise-class schedulers ñ with serious price tags ñ cannot compete with. You will see how running a specific program can be made dependent on the successful running of certain other programs, and how to separate various tasks using the built-in security mechanisms. You will learn to manage resources to balance the load on your system, and gain increased database performance.
Table of Contents (15 chapters)
Mastering Oracle Scheduler in Oracle 11g Databases
About the Author
About the Reviewers

Chapter 2. Simple Chain

At first sight, chains might look a little intimidating. Often, there is a lot of code which can be difficult to go through when you are trying to identify particular problems or issues. But fear not, things are not as bad as they seem. Chains are useful and can reduce a number of potential issues.

In many systems, problems are hidden in the form of scheduled tasks that rely on one task to be completed before the next task is started. A nice example of this is a cold backup, which is performed in three individual sections:

  1. 1. Shut down the database.

  2. 2. Copy the database files to a remote location.

  3. 3. Start up the database.

In the example above, when the cold backup was implemented, step 2 originally took four minutes. Therefore, the administrator decided that step 3 could be started five minutes after step 1 was completed. However, after a few weeks the database grew bigger and the copy phase of the backup took 20 minutes. This is what we might call a time bomb. Everything...