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
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
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
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
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
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!
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