Introduction
An RAC database is a clustered database.
There are multiple Oracle instances which are connected via "interconnect" - which is a type of LAN.
The datafiles are stored in several disk drives which are connected by "cluster aware storage".
By adding multiple instances, we can add and remove and single Oracle instance without bringing the database down. So, database always remains available. That is the essence of RAC - high availability.
An RAC database is managed by "Oracle Clusterware". RAC operates in "shared everything" architecture mode.
Any storage (eg. SAN, SCSI etc.) can be used with RAC. However, good I/O speed is required for scalability of storage.
RAC supports up to 100 clusters which may be different at hardware level but must run same operating system!
Oracle recommends using ASM (Automatic Storage Management) for ease of dealing with clustered storage.
As a reminder, the RAC is used for high availability and scalability. When work load grows, you can simply add another server to the grid (RAC is a type of grid computing after all).
RAC can be managed via Oracle Enterprise Manager.
An Oracle RAC database requires three components - cluster nodes (the servers or computers running Oracle instances), shared storage (disk drives) and Oracle Clusterware (software application).
Installing RAC
The first step of working with RAC is to install "Oracle Clusterware" which is installed via Universal Installer.
Then you have to configure the clusterware.
Then install ASM (Automatic Storage Management)
Now install Oracle 11g database
Then perform post installation tasks. This ensures that clusterware and database are installed properly and they are aware of each other.
It is possible to convert your normal single instance Oracle database to an RAC database. You can achieve this via Enterprise Manager or "rconfig" utility.
Administering Clusterware
Oracle Clusterware includes two important components: the voting disk and the OCR.
The voting disk is a file that manages information about node membership, and the OCR is a file that manages cluster and Oracle RAC database configuration information.
RAC can be administered via Oracle Enterprise manager. On EM's web console mode, click on Availability tab to see details of Clusterware. You can click on Topology tab to see a visual represntation of your nodes. The Interconnect tab shows you info on interfaces. You can also add new instance to clusterware via EM (under Server tab).
Oracle Clusterware posts alert messages in alert log - which is under $CRS_home.
RAC data dictionary views are created by catclust.sql.
Cache Fusion
Oracle RAC uses "Cache Fusion" to synchronize the data stored in the buffer cache of each database instance.
Since all computers/instances in an RAC access the same database, the overall system must guarantee the coordination of data changes on different computers such that whenever a computer queries data it receives the current version - even if another computer recently modified that data. Oracle RAC refers to this functionality as Cache Fusion. It involves the ability of AC to "fuse" in-memory data cached physically separately on each computer into a single global cache.
Recommended Reference for further reading:
Oracle Database 2 day + RAC
http://download.oracle.com/docs/cd/B28359_01/rac.111/b28252.pdf
Converting single instance database to RAC
http://www.oracle.com/technology/pub/articles/chan_sing2rac_install.html
Other
http://www.orafaq.com/wiki/RAC_FAQ
An RAC database is a clustered database.
There are multiple Oracle instances which are connected via "interconnect" - which is a type of LAN.
The datafiles are stored in several disk drives which are connected by "cluster aware storage".
By adding multiple instances, we can add and remove and single Oracle instance without bringing the database down. So, database always remains available. That is the essence of RAC - high availability.
An RAC database is managed by "Oracle Clusterware". RAC operates in "shared everything" architecture mode.
Any storage (eg. SAN, SCSI etc.) can be used with RAC. However, good I/O speed is required for scalability of storage.
RAC supports up to 100 clusters which may be different at hardware level but must run same operating system!
Oracle recommends using ASM (Automatic Storage Management) for ease of dealing with clustered storage.
As a reminder, the RAC is used for high availability and scalability. When work load grows, you can simply add another server to the grid (RAC is a type of grid computing after all).
RAC can be managed via Oracle Enterprise Manager.
An Oracle RAC database requires three components - cluster nodes (the servers or computers running Oracle instances), shared storage (disk drives) and Oracle Clusterware (software application).
Installing RAC
The first step of working with RAC is to install "Oracle Clusterware" which is installed via Universal Installer.
Then you have to configure the clusterware.
Then install ASM (Automatic Storage Management)
Now install Oracle 11g database
Then perform post installation tasks. This ensures that clusterware and database are installed properly and they are aware of each other.
It is possible to convert your normal single instance Oracle database to an RAC database. You can achieve this via Enterprise Manager or "rconfig" utility.
Administering Clusterware
Oracle Clusterware includes two important components: the voting disk and the OCR.
The voting disk is a file that manages information about node membership, and the OCR is a file that manages cluster and Oracle RAC database configuration information.
RAC can be administered via Oracle Enterprise manager. On EM's web console mode, click on Availability tab to see details of Clusterware. You can click on Topology tab to see a visual represntation of your nodes. The Interconnect tab shows you info on interfaces. You can also add new instance to clusterware via EM (under Server tab).
Oracle Clusterware posts alert messages in alert log - which is under $CRS_home.
RAC data dictionary views are created by catclust.sql.
Cache Fusion
Oracle RAC uses "Cache Fusion" to synchronize the data stored in the buffer cache of each database instance.
Since all computers/instances in an RAC access the same database, the overall system must guarantee the coordination of data changes on different computers such that whenever a computer queries data it receives the current version - even if another computer recently modified that data. Oracle RAC refers to this functionality as Cache Fusion. It involves the ability of AC to "fuse" in-memory data cached physically separately on each computer into a single global cache.
Recommended Reference for further reading:
Oracle Database 2 day + RAC
http://download.oracle.com/docs/cd/B28359_01/rac.111/b28252.pdf
Converting single instance database to RAC
http://www.oracle.com/technology/pub/articles/chan_sing2rac_install.html
Other
http://www.orafaq.com/wiki/RAC_FAQ
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