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Using Multiple Oracle Homes

Introduction

The Oracle Universal Installer supports the installation of several active Oracle homes on the same machine. An Oracle home is the system context in which Oracle products run. This context consists of the directory location where the products are installed, the corresponding system path setup, and where applicable, the program groups associated with the products installed in that home, and the services running from that home.

Multiple Oracle Homes

The Oracle Universal Installer supports the installation of several active Oracle homes on the same machine as long as the products support this at runtime. You can have multiple versions of the same product or different products running from different Oracle homes concurrently. Products installed in one home will not conflict or interact with products installed in another home. You can update software in any home at any time, assuming all Oracle applications/services/processes installed on the target home are shut down. Processes from other homes may still be running.

Target Home

The Oracle home currently accessed by the Oracle Universal Installer for installation or deinstallation is the target home. In order to upgrade or remove products from the target homes, those products must be shut down/stopped.

Product Types

Different levels of support are available with multiple Oracle homes for the following product types:

• Products that can be installed once in any new Oracle home. Ensure that the previous product installation is first removed so that only one copy/version of that application can run at the same time. If such product is already installed, and you try to install it again on a different home, the Oracle Universal Installer issues an error message.
• Products that can be installed multiple times, in different homes, on the same machine, with no conflicts or interaction at install-time, run-time, or deinstall-time. These are products which can be used concurrently.

  Note: The installation guide of your products will specify what type they are and whether they can be installed once in a home or multiple times.

Home Selector (Available on Win32 Platforms)

The following sections describe the Home Selector application, which is available when you install the Oracle Universal Installer on a Windows computer.

Overview

The Home Selector is part of the installation software and is installed with the Oracle Universal Installer. It is installed in <oui_location>\HomeSelector.

If your application is not installed in one of the Oracle homes, you need to ensure it uses the right product version, by pointing it to the right home. That specific (target) home must take precedence over the other homes in your path when you launch your application.

The Home Selector enables you to easily change your primary Oracle home (the one that appears first in the PATH environment variable). If you need to switch the active home or need to perform batch work which requires a "default home" to be active, the Oracle Home Selector can be used to change the Windows NT system settings.

When using the Home Selector to make a specific $ORACLE_HOME the active one, the software installation in question is moved to the top of the PATH variable, making it the first directory to be scanned for executables and library files.

How It Works

When you perform an install on a system, the first $ORACLE_HOME will be named the "DEFAULT_HOME" and will register itself in the Windows NT registry under the key:

  HKEY_LOCAL_MACHINE
    Software
      Oracle

This is the default Windows NT registry hive which contains all the "generic" Oracle settings. Also the PATH variable is adjusted and the BIN directory of the $ORACLE_HOME is added to the environment variable.

Starting with Oracle 8.0.4, the first version to be multiple $ORACLE_HOME aware, some additional parameters will also be written to the key:

  HKEY_LOCAL_MACHINE
    Software
      Oracle
        Home0

With the Oracle Universal Installer, you can change the "DEFAULT_HOME" name to something else. Also, it registers all Oracle settings in the "Home0" subkey of the ORACLE key.

When an additional $ORACLE_HOME is added to the system, the PATH variable is adjusted again to add the new BIN directory of the newly installed Oracle software. The registry variables are written to a key named "HOMEx," where X is the next available number in the Oracle key.

When several $ORACLE_HOMEs are installed, the executables referenced are all found in the first $ORACLE_HOME\BIN directory of the PATH variable. When you want to switch the order of the PATH variable, you can use the Home Selector to switch the order of the $ORACLE_HOMEs installed on the system.

Together with the installation and registration of the software in the registry, a second series of registry variables are written in the following key:

  HKEY_LOCAL_MACHINE
    Software
      Oracle
        ALL_HOMES

This is the starting point for the list of all $ORACLE_HOME installations, done on this system.

The following variables are written in this key:

• HOME_COUNTER: Number of Oracle home directories already present on the system. This counter is a number, exactly 1 higher as the last ID subkey present.
• LAST_HOME: ID number of the currently active $ORACLE_HOME
• IDx: List of registry key's containing the name, number and installation directory of this ORACLE_HOME. The first installation is written in ID0, the next one in ID1, etc.

If the Home Selector is started in interactive mode, the registry hive "ALL_HOMES" is read, including all subkeys, and a dialog box will be displayed with all available installations. As soon as the you select one, the PATH variable will be adjusted at the system level.

In order to make batch processing possible, this tool also has a command line interface, making it possible to use the tool to switch the PATH settings while executing a series of commands:

ohsel -switch "Oracle Home Name"

The name of this $ORACLE_HOME is one of the names found in the ID subkeys.

Oracle Home Directory Structure for Windows Platform

A typical Oracle home on Windows platforms contains the files and directories shown in Table 2-1.

Table 2-1 Oracle Home Directory for Windows Platforms

Oracle Home Directory	Contents
\BIN	Product executables and DLLs
\DBS	Common message files
\PROD1	PROD1 product files
\PROD2	PROD2 product files

Optimal Flexible Architecture Directory Structure (on Solaris)

The Optimal Flexible Architecture (OFA) standard is a set of configuration guidelines for fast, reliable Oracle databases that require little maintenance.

OFA is designed to:

• organize large amounts of complicated software and data on disk to avoid device bottlenecks and poor performance
• facilitate routine administrative tasks such as software and data backup functions, which are often vulnerable to data corruption
• alleviate switching among multiple Oracle databases
• adequately manage and administer database growth
• help eliminate fragmentation of free space in the data dictionary, isolate other fragmentation, and minimize resource contention

The OFA directory structure is described below.

ORACLE_BASE Directory

ORACLE_BASE specifies the BASE of the Oracle directory structure for OFA-compliant databases. A typical ORACLE_BASE directory structure is described in Table 2-2. When installing an OFA-compliant database using the Oracle Installer, ORACLE_BASE is by default set to /pm/app/oracle.

Table 2-2 Sample ORACLE_BASE Directory Structure and Content

Directory	Content
admin	Administrative files
doc	online documentation
local	Subtree for local Oracle software
product	Oracle software

ORACLE_HOME Directory

The following is an example of an Oracle Server Install.

If you install an OFA-compliant Oracle Server, the ORACLE_HOME directory is /mount_point/app/oracle/product/release_number. ORACLE_HOME directory structure and content are described in Table 2-3. Under UNIX, the ORACLE_HOME directory might contain the following subdirectories, as well as a subdirectory for each Oracle product selected.

Table 2-3 Sample ORACLE_HOME Directory Structure and Content

Directory	Content
assistants	configuration Assistants
bin	binaries for all products
ctx	interMedia Text cartridge
dbs	initsid.ora, lksid
install	install related files
lib	Oracle product libraries
jlib	Java classes
md	Spatial cartridge
mlx	Xerox Stemmer (for interMedia Text cartridge)
network	Net8
nlsrtl	NLS runtime loadable data
ocommon	common files for all products
odg	data gatherer
opsm	Parallel Server Manager Components
oracore	core libraries
ord	data cartridges
otrace	Oracle TRACE
plsql	PL/SQL
precomp	precompilers
rdbms	server files and libraries required for the database
slax	SLAX parser
sqlplus	SQL*Plus

Creating an Oracle Home

To create an Oracle home, follow the steps below.

1. Run the Oracle Universal Installer.
2. In the File Locations page, enter the Oracle home settings for the installation session under Destination. See Table 2-4 for a description of the fields in this section of the screen.

   Note: The Name field only appears in Windows platforms.

3. Continue with your installation. Refer to Chapter 1, "Using the Oracle Universal Installer" for detailed information.

   Table 2-4 Oracle Installation Settings in Destination  

   Settings	Functions
   Name	For Windows platforms, Oracle homes are identified by name, and the Oracle home name identifies the program group associated with a particular Oracle home, and the Oracle services installed on the associated home. The Oracle home name must be 1 to 16 characters long and can only include alphanumeric characters and underscores.
   Path	Enter an Oracle home and its full path or select an Oracle home from a drop down list of existing Oracle Homes. The Oracle home location is the directory where products are installed. List of Oracle homes on Windows platforms: All Oracle homes that are already created using the Oracle Universal Installer All homes created using the previous Oracle Installer (ORCA-based) The home that the ORACLE_HOME environment variable points to List of Oracle homes on UNIX: All Oracle homes that are already created using the Oracle Universal Installer All homes as defined in the /var/opt/oratab file The home that the ORACLE_HOME environment variable points to If none of these homes exists, a default home is calculated based on the disk volume with the largest amount of free space. Datafiles may or may not be installed within an Oracle home. You may use the Browse button to choose a directory to install your product. For Windows platforms: it must be a valid path that is not in the Windows directory. Different homes cannot share the same location.