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Oracle Concepts - DBCA Database Configuration Assistant

Oracle Tips by Burleson Consulting

DBCA Database Configuration Assistant Concepts

Now that we have chosen our ORACLE_SID, we press next to get to the next window:

This window allows us to configure Oracle Enterprise Manager (OEM). It also allows you to enable OEM options for automated backups and email notifications. At this point, we will not configure these options. Simply click on the next button to move to the next window.

The next window is very important. It allows us to set passwords on DBA level accounts (such as SYS and SYSTEM):

You can set all accounts to a common password or you can configure specific passwords for each account. In our case, let?s configure all accounts to use the same password. Let?s say our password is shadow. Hence, enter shadow in the password and confirm password boxes, and click on next.  Now Oracle asks us to choose our file system type:

In our case, we want to take the default setting. If you are creating a RAC cluster, or if you are using ASM or Raw file systems, you will want to explore the other options that DBCA makes available to you in this screen.

To move onto the next screen then, click on next.  The next screen is where we tell Oracle where it is to put database related files:

As you become a more experienced DBA, you will learn that file placement can make a big difference on database performance. In our case, we are going to allow Oracle to locate our datafiles, so we simply click on next to continue.

Configuring the Flash Recovery Area

The next screen allows us to configure the Oracle flash recovery area. This is a new feature in Oracle Database 10g, and we will be discussing it later in this book. The flash recovery area is very important because it is where Oracle stores a number of important backup and recovery files. Here is an example of the recovery options screen:

Note that we have changed two default values. First, we doubled the size of the flash recovery area (this value defaults to 2 Gigabytes (2GB), which is frequently is too small). Second, we have clicked the enable archiving checkbox.

This setting will tell Oracle to configure the database in ARCHIVELOG mode and Oracle will use the redo logging mechanism that we explained in chapter one.

The ARCHIVELOG mode also makes Oracle database backup and recovery much easier. We strongly recommend that any production Oracle database be in ARCHIVELOG mode.

We will discuss ARCHIVELOG mode in more detail later in this book. Having made the two changes we suggested, click on next.

Create Oracle Sample Schemas

Next, wee see the Sample Schemas screen:

By checking Sample Schemas, Oracle will create several small sample schemas that we can use for learning. 

As you learn Oracle and use Oracle-supplied examples, these sample schemas will come in handy. Click next to continue the database creation screen.

Configuring Memory Usage

The next screen is the memory specification, a very important part of the install:

This screen allows you to modify the initialization parameters for memory pools (db_cache_size, shared_pool_size), set your database block sizes and choose the character set for your database. In this example, we decided that the buffer cache was too small and increased it to 100 megabytes.

Deciding How Much Oracle Memory to Allocate

It is often difficult to decide how much memory to allocate to Oracle. Generally we recommend that you allocate between 40 percent of your available real memory (not swap-page memory) to Oracle. We start by allocating about 25% to the shared pool and 75% to the buffer cache.

After you have defined your initial memory allocations, you need to monitor performance and modify memory allocations as required (we talk about monitoring performance later in this book).

If you are installing Oracle on a PC, remember that a 32-bit PC can only allocate about 1,700 megabytes (1.7 gig), and you will want to keep your SGA size small, under 1,500 megabytes.  Here are some guidelines for allocating memory:

* Over-allocation ? Making your SGA too big can cause nasty things to happen on your operating system like paging and swapping of memory out to disk.  More is not always better. Only allocate as much memory as the system really needs.

* Share your RAM ? You must not take-away RAM that might be used by other programs or databases on your server.  On an Oracle-dedicated server, a general rule of thumb is to never allocate more than about 60 to 65 percent of your memory to the database. This reserves memory for other Oracle and non-Oracle processes.

Also note that the memory allocation screen allows you to change the SGA pool sizes, such and the Java pool and the all-important PGA.  Once you have changed any settings you wish to change, press next to continue.

DBCA Database Storage Settings

The next screen allows you to change any database storage parameters as seen here:

This screen allows you to add or remove tablespaces, adjust the size of the datafiles that are associated with those tablespaces, modify the online redo logs, etc. In our case, we will take the default, so press next. We are almost ready to create a database!

Sizing your Oracle database Files

As you create databases, these questions will arise:

1. How big do we make database datafiles?

Several programs out there that can help you figure out how bug your database datafiles need to be. Perhaps the most tried and true way to decide this is to create a test system and populate it with a representative set of data, say one or two percent of the size of production. Once you have done this, simply extrapolate from there how big your production database will need to be. Hence, if your test database is 10MB with one percent of the data, your production database will be 1000 MB.

2. How big do we make database Online Redo Logs

After you create your database, you will monitor how often the online redo logs switch, on average. You should size your online redo logs such that you switch online redo logs no more frequently than every 15 minutes.

Finishing the DBCA Database Creation

We have one more screen to go before Oracle can create a database. In this last screen Oracle gives us two different options with regards to the actions that DBCA should take. The first option allows us to create a template for the new database.

The second option actually instructs Oracle to create the database. Here is an example of this screen:

In our case, we are going to tell Oracle to create a database, and we will not save these settings as a database template (which we could later load and use to create another database).

Click on finish, and the DBCA will present you with a summary of all of the database creation actions that it will take.

Press OK when you see that window and Oracle will start the creation of your Oracle database. The screen you will see, as Oracle proceeds to create your database, will look something like this:

Oracle will let you know when it has completed the database creation. Depending on the speed of your system, it could take several minutes. Once the database creation is complete, you will see the following screen:

This screen gives you the opportunity to view and modify any accounts that were created by the DBCA. In our case, we should not need to modify any of the accounts so we can just press the exit button. Congratulations, you have created a database. Now lets connect to our database for the first time!

This is an excerpt from the bestselling "Easy Oracle Jumpstart" by Robert Freeman and Steve Karam (Oracle ACE and Oracle Certified Master).  It?s only $19.95 when you buy it directly from the publisher here.

If you like Oracle tuning, you may enjoy the new book "Oracle Tuning: The Definitive Reference", over 900 pages of BC's favorite tuning tips & scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  and include the URL for the page.


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