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| Re: Terminology problem [message #111196 is a reply to message #111185] |
Mon, 14 March 2005 12:15   |
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Mahesh Rajendran
Messages: 10708
Registered: March 2002
Location: oracleDocoVille
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Senior Member
Account Moderator |
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depends on your need.
You may want to have 1 database ( with 1 instance. if you need more instances you need to have a RAC. real application cluster).
within this 1 database you can have 3 different schemas.
schema is the logical area for an user.
so creating an user is nothing bu creating a schema to hold the objects for the user. ( ALMOST).
the simple case is
all the three apps need different set of data.
the above scheme works ( 3 different users..one for each app..in 1 database).
the complex case is
is what we call as FGAC ( Fine grained access control)which you may not want.
a simple (may not be exactly correct) example for this
is like when you login to your online banking account, you see ONLY YOUR DETAILS.
but still the banking database holds information for all the accounts.
>>My terminology problem is the following : am I right if I say "I want to create a database containing 3 instances" or do I want to create3 databases ?
You dont need to create 3 databases.
all the three apps/users can go into 1 database.
>>that is the difference between a schema and an instance ?
schema is logical area for user.
I create user SCOTT and user SCOTT has his objects all logically grouped in his own schema called SCOTT.
thats it.
one or many such schemas make a database.
there can be one or many databases in one server.
each database is identified by ORACLE_SID for process levels.
< quoting docs >
Every running Oracle database is associated with an Oracle instance. When a database is started on a database server (regardless of the type of computer), Oracle allocates a memory area called the System Global Area (SGA) and starts one or more Oracle processes. This combination of the SGA and the Oracle processes is called an Oracle instance. The memory and processes of an instance manage the associated database's data efficiently and serve the one or multiple users of the database.
< /quoting docs >
you cannot have two identical ORACLE_SID in the same machine.
a RAC ( real application cluster) will do that.
RAC has many instances for the same database acroos many servers (nodes).
SO if one instance or server goes down, still the database is available through other instance.
please refer documentation titled ORACLE CONCEPTS from
oracle.com or tahiti.oracle.com.
YOu get all information you need
[Updated on: Mon, 14 March 2005 12:17] Report message to a moderator |
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