ORACLE RAC DBA ONLINE TRAINING
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ORACLE RAC DBA ONLINE TRAINING
A cluster comprises multiple interconnected computers or servers that appear as if they are one server to end users and applications. Oracle Real Application Clusters (Oracle RAC) enables you to cluster Oracle databases. Oracle RAC uses Oracle Clusterware for the infrastructure to bind multiple servers so they operate as a single system.
Oracle Clusterware is a portable cluster management solution that is integrated with the Oracle database. Oracle Clusterware is also a required component for using Oracle RAC. In addition, Oracle Clusterware enables both single-instance Oracle databases and Oracle RAC databases to use the Oracle high-availability infrastructure. Oracle Clusterware enables you to create a clustered pool of storage to be used by any combination of single-instance and Oracle RAC databases.
Oracle Clusterware is the only clusterware that you need for most platforms on which Oracle RAC operates. You can also use clusterware from other vendors if the clusterware is certified for Oracle RAC.
In database computing, Oracle Real Application Clusters (RAC) an option for the Oracle Database software produced by Oracle Corporation and introduced in 2001 with Oracle9i � provides software for clustering and high availability in Oracle database environments. Oracle Corporation includes RAC with the Standard Edition of Oracle Database, but makes it an extra-charge option for the Enterprise Edition.
Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering.
In a non-RAC Oracle database, a single instance accesses a single database. The database consists of a collection of data files, control files, and redo logs located on disk. The instance comprises the collection of Oracle-related memory and operating system processes that run on a computer system.
In an Oracle RAC environment, two or more computers (each with an Oracle RDBMS instance) concurrently access a single database. This allows an application or user to connect to either computer and have access to a single coordinated set of data.
When one computer is not powerful 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 processes for accomplishing these 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 instances 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.
The main aim of Oracle RAC is to implement a clustered database to provide performance, scalability and resilience.
Oracle RAC depends on the infrastructure component Oracle Clusterware to coordinate multiple servers and their sharing of data storage.The FAN (Fast Application Notification) technology detects down-states.
Prior to Oracle 9, network-clustered Oracle databases used a storage device as the data-transfer medium (meaning that one node would write a data block to disk and another node would read that data from the same disk), which had the inherent disadvantage of lackluster performance. Oracle 9i addressed this issue: RAC uses a dedicated network connection for communications internal to the cluster.
Since all computers/instances in a 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. Cache Fusion involves the ability of Oracle RAC to “fuse” the in-memory data cached physically separately on each computer into a single, global cache.
Oracle Real Application Clusters One Node (RAC One Node) applies RAC to single-node installations running Oracle Database 11g Release 2 Enterprise Edition.
Relative to the single-instance Oracle database, Oracle RAC adds additional complexity. While database automation makes sense for single-instance databases, it becomes even more necessary for clustered databases because of their increased complexity.
Oracle Real Application Clusters (RAC), introduced with Oracle9i in 2001, supersedes the Oracle Parallel Server (OPS) database option. Whereas Oracle9i required an external clusterware (known as vendor clusterware like Veritas or Sun Cluster) for most of the Unix flavors (except for Linux and Windows where Oracle provided free clusterware called Cluster Ready Services or CRS), as of Oracle 10g, Oracle’s clusterware product was available for all operating systems. With the release of Oracle Database 10g Release 2 (10.2), Cluster Ready Services was renamed to Oracle Clusterware. When using Oracle 10g or higher, Oracle Clusterware is the only clusterware that you need for most platforms on which Oracle RAC operates (except for Tru cluster, in which case you need vendor clusterware). You can still use clusterware from other vendors, if the clusterware is certified for Oracle RAC.
In RAC, the write-transaction must take ownership of the relevant area of the database: typically, this involves a request across the cluster interconnection (local IP network) to transfer the data-block ownership from another node to the one wishing to do the write. This takes a relatively long time (from a few to tens of milliseconds) compared to single database-node using in-memory operations. For many types of applications, the time spent coordinating block access across systems is low relative to the many operations on the system, and RAC will scale comparably to a single system. Moreover, high read-transactional databases (such as data-warehousing applications) work very well under RAC, as no need for ownership-transfer exists. (Oracle 11g has made many enhancements in this area and performs a lot better than earlier versions for read-only workloads.)
The overhead on the resource mastering (or ownership-transfer) is minimal for fewer than three nodes, as the request for any resource in the cluster can be obtained in a maximum of three hops (owner-master-requestor). This makes Oracle RAC horizontally scalable with many nodes. Application vendors (such as SAP) use Oracle RAC to demonstrate the scalability of their application. Most of the biggest OLTP benchmarks are on Oracle RAC. Oracle RAC 11g supports up to 100 nodes.
For some applications, RAC may require careful application partitioning to enhance performance. An application that scales linearly on an SMP machine may scale linearly under RAC. However, if the application cannot scale linearly on SMP, it will not scale when ported to RAC. In short, the application scalability is based on how well the application scales in a single instance.
Oracle Clusterware provides a complete, integrated clusterware management solution on all Oracle Database platforms. This clusterware functionality provides all of the features required to manage your cluster database including node membership, group services, global resource management, and high availability functions. You can install Oracle Clusterware independently or as a prerequisite to the Oracle RAC installation process. Oracle database features such as services use the underlying Oracle Clusterware mechanisms to provide their capabilities. Oracle also continues to support select third-party clusterware products on specified platforms
Oracle Clusterware is designed for, and tightly integrated with, Oracle RAC. When you create an Oracle RAC database using any of the management tools, the database is registered with and managed by Oracle Clusterware, along with the other Oracle processes such as Virtual Internet Protocol (VIP) address, Global Services Daemon (GSD), the Oracle Notification Service (ONS), and the Oracle Net listeners. These resources are automatically started when Oracle Clusterware starts the node and automatically restarted if they fail. The Oracle Clusterware daemons run on each node.
You can use Oracle Clusterware to manage high-availability operations in a cluster. Anything that Oracle Clusterware manages is known as a CRS resource, which could be a database, an instance, a service, a listener, a VIP address, an application process, and so on. Oracle Clusterware manages CRS resources based on the resource’s configuration information that is stored in the Oracle Cluster Registry (OCR). You can use SRVCTL commands to administer other node resources.
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