2 Multiple Oracle Homes and Optimal Flexible Architecture

What Is an Oracle Home?

An Oracle home corresponds to the environment in which Oracle products run. This environment includes the following:

• Location of installed product files

• PATH variable pointing to binary files of installed products

• Registry entries

• Service names

• Program groups

Oracle homes also have a name associated with them, which you specify along with their location during installation.

Benefit of Using Multiple Oracle Homes

The main benefit of using multiple Oracle homes is that you can run multiple releases of the same products concurrently. For example, you can test an Oracle Database patch before you run your production Oracle Database against it.

One-Listener Support of Multiple Oracle Homes

You can use one listener for spawning connections to databases for multiple Oracle homes. Simply add each system identifier to the SID_LIST section in the ORACLE_BASE\ORACLE_HOME\network\admin\listener.ora file.

Because the SID is unique to a system across different Oracle homes, the listener can spawn the database thread for a specific SID in the correct Oracle home, and the ORACLE_HOME parameter (used in UNIX environments only) is not needed in the listener.ora file.

Changing the Value of PATH Using Oracle Universal Installer

Oracle Universal Installer enables you to edit your environment PATH to make a specific Oracle home directory your primary home when you have multiple active Oracle home directories on a single computer.

1. Choose Start > Programs > Oracle > HOME_NAME > Oracle Installation Products > Universal Installer.

   The Oracle Universal Installer: Welcome window appears.

2. Click Installed Products.

3. Select the Environment tab.

4. Select a primary Oracle home and use the up arrow to move it to the top of the list.

5. Click Apply.

6. Click Close.

Changing the Value of PATH at the System Level

PATH is an environment variable, and the procedure for changing its value depends on your operating system.

Changing the Value of PATH at the Command Prompt

At the command prompt, enter:

C:\> set PATH=PATHNAME;%PATH%

where PATHNAME is the full path to binary files for the products you want to use. This change is valid for the current session only. If you want to change the value of your PATH permanently, then use Oracle Universal Installer or change the value of PATH at the system level. Both methods are described earlier in this section.

Setting ORACLE_HOME

Oracle recommends that you never set the ORACLE_HOME environment variable, because it is not required for Oracle products to function properly. If you set the ORACLE_HOME environment variable, then Oracle Universal Installer will unset it for you. Oracle products find the value of ORACLE_HOME at the location specified by the ORACLE_BASE\ORACLE_HOME\bin\oracle.key file. If you must set ORACLE_HOME in the environment for another reason, then you must take care to run software only from that Oracle home when the variable is set.

When you run an Oracle application from the command prompt, the first executable by that name found in the directory path runs. For example, C:\> sqlplus. Alternately, if you specify a full directory path, then the specified application runs. For example, C:\oracle\ora82> sqlplus.

If you modify the value of PATH using any of the three methods described in the previous section, then you can choose which release of an application is run from the command prompt. In sum, modifying the value of PATH indicates from which Oracle home to run executables at the command prompt, when no full directory path is specified.

Once an Oracle application starts, it looks for all environment variables first in the current environment and second in the registry key for the Oracle home from which the application is running.

The application knows where it is running from by calling Windows to obtain the executable's path name and then parsing the path name to get the directory from which it is running. In the ORACLE_BASE\ORACLE_HOME\bin directory where the executable resides, there is a file called oracle.key. This file specifies where in the registry to look for variables when applications from that particular Oracle home are run.

For example, if you run C:\oracle\ora82\bin\sqlplus.exe, then sqlplus.exe looks in C:\oracle\ora82\bin\oracle.key to find out where to look for its registry variables. If the oracle.key file does not exist (for version 7 and some version 8 Oracle homes), then Oracle uses HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE to locate the registry variables.

In a typical case, there are no Oracle variables (that is, ORACLE_HOME) set in the environment. Any applications run from an Oracle8 release 8.0.5 or later Oracle home look in the oracle.key file in that Oracle home and find their variables (including ORACLE_HOME) in the correct registry key. Likewise for Oracle Database 10g, the Oracle home that gets priority depends on the PATH, but regardless of the PATH setting, all software works correctly.

Setting TNS_ADMIN

Oracle software looks for TNS_ADMIN in one location in the registry (depending upon the type of Oracle home installed). If you installed software into the default Oracle home, then any software running from that Oracle home will look in HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE. If you installed a new-style (8.0.4 or later) multiple Oracle home, then the Oracle software looks in HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOMEID.

The environment always overrides the registry, so if TNS_ADMIN is set in the environment, then that takes precedence over the TNS_ADMIN setting in the registry.

Benefits of an OFA-Compliant Database

An OFA-compliant database has the following benefits:

• Easier database administration and management of database growth

  File system organization simplifies locating specific database files and adding database files as the database grows.

• Fewer performance bottlenecks

  Disk contention decreases, because Oracle administration files, binary files, and datafiles that used to be on one disk can now reside in separate directories on separate disks.

• Safeguards against disk failures

  By spreading files across more than one disk, disk failures impact as little data as possible.

• Support for concurrent execution of application software

  Multiple releases of application software can run simultaneously, enabling testing and use of a new release of an application before abandoning the previous release. Transferring to a new release after an upgrade is simple for the database administrator and transparent for the user.

Characteristics of an OFA-Compliant Database

An OFA-compliant database has the following characteristics:

• Independent subdirectories

  Categories of files are separated into independent subdirectories so that files in one category are minimally affected by operations on files in other categories.

• Consistent naming conventions for database files

  Database files are easily distinguishable from all other files. Files of one database are easily distinguishable from files of another database. Datafiles, redo log files, and control files are easily identifiable. Datafiles are clearly associated with a particular tablespace.

• Integrity of Oracle home directories

  You can add, move, or delete Oracle home directories without having to revise applications that refer to them.

• Separation of administrative information for each database

  The ability to distinguish administrative information about one database from that of another ensures a reasonable structure for the organization and storage of administrative data.

• Separation of tablespace contents

  Tablespace free space fragmentation and I/O request contention are minimized, while administrative flexibility is maximized.

• Tuning I/O loads across all disks

  I/O loads are tuned across all disks, including disks storing Oracle data in raw devices, if needed.

Top-Level Oracle Directory

When you install an Oracle8i release 8.1.3 or earlier release, all subdirectories are located under a top-level ORACLE_HOME directory that by default is C:\orant.

When you install an Oracle8i release 8.1.4 or later OFA-compliant database, all subdirectories are no longer under a top-level ORACLE_HOME directory. There is now a new top-level directory called ORACLE_BASE of form X:\oracle, where X is any hard drive. If you install an OFA-compliant database using Oracle Universal Installer defaults, then ORACLE_BASE is C:\oracle.

ORACLE_BASE contains \ORACLE_HOME directories, \oradata directories (for database files), and \admin directories (for database administration files).

Database Filenames

In Oracle8i release 8.1.3 and earlier releases, database files have the SID in the database filename. For example, the first control file is named ctl1SID.ora.

Beginning with Oracle8i release 8.1.4, database files no longer have the SID in the database filename. For example, the first control file is named control01.ctl. There is no need for the presence of the SID in the filename, because all the database files for a particular database are placed in \oradata under a directory called DB_NAME that is named for that database.

Database Filename Extensions

In Oracle8i release 8.1.3 and earlier releases, all database files have the same ".ORA" extension.

In an OFA-compliant release, the convention of having ".ora" as the filename extension for database files is no longer used. Database filenames now have more meaningful extensions. These are:

• .ctl for control files,

• .log for log files

• .dbf for datafiles.

ORACLE_BASE Directory

ORACLE_BASE is the root of the Oracle directory tree. If you install an OFA-compliant database using Oracle Universal Installer defaults, then ORACLE_BASE is X:\oracle where X is any hard drive. For example, C:\oracle.

If you are installing Oracle Database for Windows on a computer with no other Oracle software installed, then you can change ORACLE_BASE before running Oracle Universal Installer. Most users will not need or want to do this.

Do not change the value of ORACLE_BASE after you run Oracle Universal Installer for the first time. If there is an existing ORACLE_BASE and you change it, then there will be a conflict of Oracle base directories. If you create another ORACLE_BASE when the original ORACLE_BASE already exists, then certain tools and the database will not be able to find previously created files. They will look for them in the new ORACLE_BASE instead of the original ORACLE_BASE.

ORACLE_HOME Directory

The \ORACLE_HOME directory is located beneath X:\ORACLE_BASE and contains subdirectories for Oracle software executables and network files.

If you install Oracle Database for Windows on a computer with no other Oracle software installed and you use default settings, then the first Oracle home directory that you create is called \ora10.

ADMIN Directory

Database administration files are stored in subdirectories of ORACLE_BASE \admin\DB_NAME. Names and brief descriptions of some of these subdirectories are:

\bdump     --background process trace files
\cdump     --core dump files
\create    --database creation files
\exp       --database export files
\pfile     --initialization parameter files
\udump     --user SQL trace files

ORADATA Directory

Database files are stored in ORACLE_BASE\ORADATA\DB_NAME. Names and brief descriptions of these files are:

control01.ctl   --control file 1
control02.ctl   --control file 2
control02.ctl   --control file 3
system01.dbf    --SYSTEM tablespace datafile
temp01.dbf      --TEMP tablespace datafile
users01.dbf     --USERS tablespace datafile
*.dbf           --datafiles corresponding to each tablespace in your database
redo01.log      --redo log file group one, member one
redo02.log      --redo log file group two, member one
redo03.log      --redo log file group three, member one

DB_NAME Directory

DB_NAME is the unique name for a particular database and has the same value as parameter DB_NAME in the initialization parameter file. When you create a database, DB_NAME can be no more than eight characters long and can contain only the following characters:

• Alphabetic characters

• Numbers

• Underscores (_)

• Pound sign (#)

• Dollar sign ($)

Specifying an ORACLE_HOME Directory

To install an OFA-compliant database, you must specify an Oracle home directory in the Path field of Oracle Universal Installer. It is of the form:

X:\[PATHNAME]\oracle\HOME_NAME 

where:

• X:\ is any hard drive. For example, C:\

• [PATHNAME] is an optional directory path name

• \oracle is a mandatory directory path name, unless you changed the value of registry key ORACLE_BASE before performing the installation

• HOME_NAME is the name of the Oracle home

The following are examples of OFA-compliant Oracle home directories:

• C:\test\oracle\ora10

• D:\oracle\ora10

Installing a Default OFA Database: Example

1. Install any Oracle Database that supports OFA (Oracle Database 8.1.6 or later) on a computer with no other Oracle software installed and make sure that you accept default settings for the Oracle home (for example, c:\oracle\ora81).

2. Install any Oracle Database (for example, Oracle Database 10g) in a second Oracle home accepting the default settings.

Table 2-1 shows the default OFA database settings.

Installing a Nondefault OFA Database: Example 1

1. Install any Oracle Database that supports OFA (Oracle Database 8.1.6 or later) on a computer with no other Oracle software installed and change default Oracle Universal Installer settings for the first Oracle home (for example, from C:\oracle\ora81 to X:\xyz).

2. Install any Oracle Database (for example, Oracle Database 10g) in a second Oracle home and change default Oracle Universal Installer settings for the second Oracle home (for example, from C:\oracle\ora10 to Y:\abc).

Table 2-2 shows the nondefault OFA database settings for example 1.

The resulting directory tree would look similar to this:

X:\xyz
     \admin
          \DB_NAME1 
          \DB_NAME2 
     \bin
     \network
     \oradata
          \DB_NAME1 
               control01.ctl
               control02.ctl
               control03.ctl
               indx01.dbf
               rbs01.dbf
               system01.dbf
               temp01.dbf
               users01.dbf
               redo01.log
               redo02.log
               redo03.log
          \DB_NAME2 
 Y:\abc
     \admin
          \DB_NAME1
          \DB_NAME2
     \bin
     \network
     \oradata
          \DB_NAME1
               control01.ctl
               control02.ctl
               control03.ctl
               indx01.dbf
               rbs01.dbf
               system01.dbf
               temp01.dbf
               users01.dbf
               redo01.log
               redo02.log
               redo03.log
          \DB_NAME2

Installing a Nondefault OFA Database: Example 2

1. Install any Oracle Database that supports OFA (Oracle Database 8.1.6 or later) on a computer with no other Oracle software installed and change default Oracle Universal Installer settings for the first Oracle home (for example, from C:\oracle\ora81 to X:\xyz\oracle\abc).

2. Install any Oracle Database and change default Oracle Universal Installer settings for the second Oracle home (for example, from C:\oracle\ora10 to X:\pqr).

Table 2-3 shows the nondefault OFA database settings for example 2.

The resulting directory tree would look similar to this:

X:\pqr                         --Oracle home 2
  \bin
  \network
X:\xyz
    \oracle                    --ORACLE_BASE for both Oracle homes
      \abc                     --Oracle home 1
        \bin
        \network
      \admin
        \DB_NAME1 
          \adhoc
          \bdump
          \cdump
          \create
          \exp
          \pfile
          \udump
        \DB_NAME2 
          \...
      \oradata
        \DB_NAME1 
          control01.ctl
          control02.ctl
          control03.ctl
          indx01.dbf
          rbs01.dbf
          system01.dbf
          temp01.dbf
          users01.dbf
          redo01.log
          redo02.log
          redo03.log
        \DB_NAME2 

Disk Mirroring

Oracle Database log files and database files can be separated and treated with different levels of hardware reliability. Oracle Database log files are highly reliable to start with, because they are stored redundantly. Creating similar reliability for database files may require you to duplicate all of your data, using disk mirrors.

Disk mirroring usually involves two or more identical drives and either a hardware controller or Windows Disk Administrator. If one disk fails, then the other disk(s) can be used to recover data that would otherwise be lost. Using one of the disks to recover lost data may involve "breaking" the mirror. If the mirror breaks, then you must build a new mirror.

Disk mirroring is part of some levels of Redundant Array of Independent Disks (RAID) configurations, provided by the disk controller. The RAID level determines the amount of redundancy. Some RAID levels can use the "hot swapping" feature, which means that you can replace a bad disk with a good one without turning off the computer or losing functionality.

Disk Striping

How you set up disks for use in a database depends on the number of disks and the type of hard disk controllers available. If the hard disk controllers support both striping and mirroring, then Oracle recommends you configure the controllers to support striping.

Some controllers are configured at system startup time by issuing a keyboard sequence that brings up configuration programs written by the controller manufacturer. One goal is to stripe as many drives together as possible by configuring the controllers. Each stripe shows up as one logical device.

Striping provides significant performance advantages. All the space from the striped drives appears as a single logical drive. Furthermore, the space is used by interlacing "stripes" of space from all of the disks in the stripe. This means that a large file uses some space from the first disk, then some from the second disk and so on to the last disk and then starting back at the first disk again. Each file can be spread over all of the striped disks. Data in such a file may be accessed randomly by more than one CPU without contention.

Controllers that support striping usually provide caching as well. This means that data can be written to the controller and cached and saved for a time in storage not on the disk. Data that is read can be cached on the controller in a similar fashion. Read caching is not necessary for Oracle Database, because all database reads are cached already in the System Global Area (SGA). The value of parameter DB_CACHE_SIZE in the initialization parameter file (init.ora) determines the buffer size that can be used in the SGA. This value also configures Oracle Database on startup.

Using Raw Partitions for Tablespaces

A raw partition is a portion of a physical disk that is accessed at the lowest possible level. I/O of a raw partition improves performance by approximately 5% to 10% compared to I/O of a partition containing a file system. Therefore, Oracle encourages you to use raw partitions for your tablespace files.

Directory Naming

Top-level names of the OFA directory tree differ between Windows and UNIX. However, main subdirectory and filenames are the same on both operating systems.

ORACLE_BASE Directory

On Windows, ORACLE_BASE is associated with an Oracle home directory. ORACLE_BASE is defined in the registry (for example, in HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\KEY_HOME_NAME).

On UNIX, ORACLE_BASE is associated with a UNIX user's environment.

Support for Symbolic Links on Windows

The goal of OFA is to place all Oracle software under one ORACLE_BASE directory and to spread files across different physical drives as your databases increase in size.

On UNIX, although everything seems to be in one directory on the same hard drive, files can be on different hard drives if they are symbolically linked or have that directory as a mount point.

Windows currently does not support symbolic links, so datafiles will not all show up under a single directory like on UNIX. Instead, you may have oradata directories on multiple drives, with datafiles in each one. In this way, you still get OFA benefits, even though datafiles are not all visible in a single directory.

Oracle recommends that you use one logical drive to store your database administration files and that you place other files, as needed, on other logical drives in an oradata\DB_NAME directory.

In the following example, there are four logical drives for a database named prod:

• C:\ contains an Oracle home and database administration files.

• F:\ contains redo log files. (F:\ drive could also represent two physical drives that have been striped to increase performance.)

• G:\ contains one of the control files and all tablespace files. (G:\ drive could also use a RAID Level-5 configuration to increase reliability.)

• H:\ contains the second control file.

The directory structure would look similar to this:

C:\oracle             --First logical drive
    \ora10            --Oracle home
      \bin            --Subtree for Oracle binaries
      \network        --Subtree for Oracle Net
      \...
    \admin            --Subtree for database administration files
      \prod           --Subtree for prod database administration files
        \adhoc        --Ad hoc SQL scripts
        \adump        --Audit files
        \bdump        --Background process trace files
        \cdump        --Core dump files
        \create       --Database creation files
        \exp          --Database export files
        \pfile        --Initialization parameter file
        \udump        --User SQL trace files

F:\oracle             --Second logical drive (two physical drives, striped)
    \oradata          --Subtree for Oracle Database files
      \prod           --Subtree for prod database files
        redo01.log    --Redo log file group one, member one
        redo02.log    --Redo log file group two, member one
        redo03.log    --Redo log file group three, member one

G:\oracle             --Third logical drive (RAID level 5 configuration)
    \oradata          --Subtree for Oracle Database files
      \prod           --Subtree for prod database files
        control01.ctl --Control file 1
        indx01.dbf    --Index tablespace datafile
        rbs01.dbf     --Rollback tablespace datafile
        system01.dbf  --System tablespace datafile
        temp01.dbf    --Temporary tablespace datafile
        users01.dbf   --Users tablespace datafile

H:\oracle             --Fourth logical drive
    \oradata          --Subtree for Oracle Database files
      \prod           --Subtree for prod database files
        control02.ctl --Control file 2