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 Oracle RAC (Real Application Cluster)

 

     When one computer is not powerfull enough for an Oracle database, the solution is to use more computers for a database. In this case we will have one database, but more computers will use the same database. As you probably know, the database is not more than some files used for keeping data and managing that data. To access that data we need same processes, memory used by the these processes for accomplishing this tasks. These form an instance. So, an instance or more instances are accessing the database. So, all the time the database is on the disks (temporarily, parts of that information are loaded in memory for the management of the database, application data). 

      When more instances are used to access the same data (database) we need to put that insnces in a cluster. The clusterware, assure that the management of data is done correctly (for instance, the same data is not modified in the same time by 2 users, even if the users access the database by 2 or more instances). The clusterware can be bought from another vendor than the database vendor. Oracle offers a solution for the clusterware as well. In this case we speak about the Oracle clusterware. When the Oracle database is installed on a clusterware (Oracle or not) we speak about an Oracle RAC or Oracle Real Application Cluster. The Oracle RAC and Oracle clusterware is not necessarily the same thing. The Oracle RAC installation includes the Oracle clusterware installation.

 


      Here is an image which show how the Oracle Real Application Cluster (Oracle RAC is working):

 

Oracle RAC architecture

 


Here are some links related to the Oracle RAC which may interest you:

 

Oracle RAC Architecture

Oracle RAC clusterware startup sequence (11gR2)

CRSCTL command (in Oracle 11gR2)

SRVCTL command (in Oracle 11gR2)

Oracle RAC Services Administration (11gR2)

Add a node to an Oracle RAC 10g

OCR file & Voting disk in an Oracle RAC Clusterware

Oracle 11gR2 RAC installation on AIX

 

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