What is oracle rac

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More related articles in Computer Networks. This ability to access all disks, allows instance recovery after an instance failure has occurred. All surviving nodes automatically absorb the failed instance? A RAC cluster provides for automatic shared execution of Oracle applications. This means that for any Oracle instance application, all queries and other processing are automatically shared among all of the servers in the RAC cluster.

The sharing of application processing by all servers in the RAC cluster leads to automatic load balancing across all cluster members. The ability of a RAC cluster to provide shared application execution and automatic load balancing, leads to the true scalability of applications without code or data changes. The Version 7. A DB block ping would occur when an instance participating in an OPS database had a block in its cache that another participating instance required.

In OPS, if another instance required the block in the cache of a second instance, the block would have to be written out to disk, the locks transferred, and then the block re-read into the requesting instance. With OPS, scalability was always an issue. OPS implementations used to suffer from tedious application design and coding, database management issues.

There were many performance issues reported. Oracle 8i OPS implementation brought in many significant changes. Server-side work such as Oracle Scheduler, Parallel Query, and Oracle Streams queues set the service name as part of the workload definition.

For Oracle Scheduler, jobs are assigned to job classes and job classes execute within services. For Parallel Query and Parallel DML, the query coordinator connects to a service and the parallel query slaves inherit the service for the duration of the parallel execution. For Oracle Streams, streams queues are accessed using services.

Work executing under a service inherits the thresholds and attributes for the service and is measured as part of the service. Oracle Database Resource Manager binds services to consumer groups and priorities. This allows the database to manage the services in the order of their importance.

For example, the DBA can define separate services for high priority online users and lower priority internal reporting applications. Likewise, the DBA can define Gold, Silver and Bronze services to prioritize the order in which requests are serviced for the same application. When planning the services for a system, the plan should include the priority of each service relative to the other services.

In this way, Oracle Database Resource Manager can satisfy the priority-one services first, followed by the priority-two services, and so on. Oracle Database automatically creates one database service when the database is created but the behavior of this service is different from that of database services that you subsequently create.

To enable more flexibility in the management of a workload using the database, Oracle Database enables you to create multiple services and specify on which instances or in which server pools the services start. If you are interested in greater workload management flexibility, then continue reading this chapter to understand the added features that you can use with services.

Dynamic database services enable you to manage workload distributions to provide optimal performance for users and applications. Dynamic database services offer the following features:. Services : Oracle Database provides a powerful automatic workload management facility, called services, to enable the enterprise grid vision. Services are entities that you can define in Oracle RAC databases that enable you to group database workloads, route work to the optimal instances that are assigned to offer the service, and achieve high availability for planned and unplanned actions.

NET clients. Transaction Guard : A tool that provides a protocol and an API for at-most-once execution of transactions in case of unplanned outages and duplicate submissions. Application Continuity : Provides a general purpose infrastructure that replays the in-flight request when a recoverable error is received, masking many system, communication, and storage outages, and hardware failures.

Unlike existing recovery technologies, this feature attempts to recover the transactional and non-transactional session states beneath the application, so that the outage appears to the application as a delayed execution.

Connection Load Balancing : A feature of Oracle Net Services that balances incoming connections across all of the instances that provide the requested database service. Load Balancing Advisory : Provides information to applications about the current service levels that the database and its instances are providing. The load balancing advisory makes recommendations to applications about where to direct application requests to obtain the best service based on the management policy that you have defined for that service.

Load balancing advisory events are published through Oracle Notification Service. Server generated alerts can be created for these metrics when they exceed or fail to meet certain thresholds.

Runtime Connection Load Balancing : This is the ability of Oracle Clients to provide intelligent allocations of connections in the connection pool based on the current service level provided by the database instances when applications request a connection to complete some work.

You can deploy Oracle RAC and noncluster Oracle database environments to use dynamic database service features in many different ways. Depending on the number of nodes and your environment's complexity and objectives, your choices for optimal automatic workload management and high-availability configuration depend on several considerations that are described in this chapter. Administrator-managed deployment is based on the Oracle RAC deployment types that existed before Oracle Database 11 g release 2 Policy-managed deployment is based on server pools , where database services run within a server pool as singleton or uniform across all of the servers in the server pool.

Databases are deployed in one or more server pools and the size of the server pools determine the number of database instances in the deployment. Server pools logically apportion a cluster into groups of servers offering database or application services.

Server pool properties control the scalability and availability of those databases and applications. You can configure each server pool with a minimum and maximum size, which determines scalability. Oracle Clusterware manages availability between server pools, and you can further regulate availability by configuring the importance value of individual server pools. Servers are not assigned to server pools by name but by number.

Therefore, you must configure any server to run any database. If you cannot configure servers due to, for example, heterogeneous servers or storage connectivity, then you can restrict servers by using server category definitions to determine server pool membership eligibility.

Minimum and Maximum Number of Servers. Consider a four-node cluster configured into two server pools named online and backoffice. A database named dbsales runs in the online server pool offering the browse , search , and salescart services. A database named dberp runs in the backoffice server pool and offers the inventory and shipping services, as shown in Figure During normal business hours the enterprise requires a minimum of two instances of the dbsales database and one instance of the dberp database to meet normal demand.

Configured this way, Oracle Clusterware ensures that there are always two servers in the online server pool and one server in the backoffice server pool.

Because this is a four-node cluster, there is one server left not assigned to either server pool. In this case, the server is a shareable resource that can be relocated online to join the server pool where it is required.

For example, during business hours the server could be given to the online server pool to add an instance of the dbsales database but after hours could be relocated to the backoffice server pool, adding a dberp database instance. All such movements are online and instances are shut down, transactionally. These two policy-managed databases are running only the instances that are required and they can be dynamically increased or decreased to meet demand or business requirements.

In contrast to administrator-managed databases, you can configure server pools with different importance levels to determine which databases are started first and which databases remain online in case there is a multinode outage. Consider a four-node cluster that hosts a database named dbapps in two server pools, sales and backoffice. Two services, orderentry and billing , run in the sales server pool, while two other services, erp and reports , run in the backoffice server pool, as shown in Figure You can use several different approaches, either discretely or combined, to consolidate Oracle databases.

Policy-managed deployments facilitate consolidation. In the case of schema consolidation, where multiple applications are being hosted in a single database separated into discrete schemas or pluggable databases PDBs , you can use server pools to meet required capacity.

Because of the dynamic scaling property of server pools, you can increase or decrease the number of database instances to meet current demand or business requirements.

Since server pools also determine which services run together or separately, you can configure and maintain required affinity or isolation. When it is not possible to use schema consolidation because of, for example, version requirements, you can host multiple databases on a single set of servers. By contrast, with administrator-managed databases, you are required to reserve capacity on each server to absorb workload failing over should a database instance or server fail.

When the failure of a server brings a server pool to below its configured minimum number of servers, another server will move from a less important server pool to take its place and bring the number of servers back up to the configured minimum. This eliminates the risk of cascade failures due to overloading the remaining servers and enables you to significantly reduce or even eliminate the need to reserve capacity for handling failures.

Migrating or converting to policy-managed databases also enables cluster consolidation and creates larger clusters that have greater availability and scalability because of the increased number of servers available to host and scale databases. Because policy-managed databases do not require binding their instance names to a particular server and binding services to particular instances, the complexity of configuring and managing large clusters is greatly reduced.

An example deployment is shown in Figure where the previous two cluster examples shown in Figure and Figure are consolidated into a single cluster, making use of both database consolidation using instance caging and cluster consolidation using server pools configured so that workloads are properly sized and prioritized.

When you deploy a policy-managed database you must first determine the services and their required sizing, taking into account that services cannot span server pools.

If you are going to collocate the server pools for this database with other server pools, then consider configuring the server pools to adjust the server pool sizes on a calendar or event basis to optimize meeting demand and business requirements. You, as the cluster administrator, create policy-managed database server pools using the srvctl add serverpool command. You can modify the properties of the server pool using the srvctl modify serverpool command in the Oracle Grid Infrastructure home.

While it is possible to create a server pool using DBCA, Oracle recommends this only for small, single server pool deployments, because DBCA will fail if servers are already allocated to other server pools. Additionally, if the cluster is made up of servers with different capacities, such as old and new servers, Oracle recommends that you set up server category definitions defining the minimum server requirements for a server to join each server pool.

After you create the server pools, you can run DBCA from the appropriate database home. Depending on the database type and task, you will be presented with different default options. If you are upgrading your database from an administrator-managed database or a database earlier than Oracle Database 11 g release 2 After you upgrade, however, you can convert the database to policy managed using the srvctl modify database command. The underscore is required so that the database can automatically create instances when a server pool grows in size.

Managing a policy-managed database requires less configuration and reconfiguration steps than an administrator-managed one with respect to creation, sizing, patching, and load balancing.

Also, because any server in the server pools within the cluster can run any of the databases, you do not have to create and maintain database instance-to-node-name mappings. You can perform maintenance tasks such as patching by relocating servers into the Free pool or by adjusting the server pool minimum and maximum sizes, thereby retaining required availability.

Policy-managed databases also facilitate the management of services, because they are assigned to a single server pool and run as singletons or uniform across all servers in the pool.

You no longer have to create or maintain explicit preferred and available database instance lists for each service. If a server moves into a server pool because of manual relocation or a high availability event, all uniform services and their dependent database instances are automatically started. If a server hosting one or more singleton services goes down, those services will automatically be started on one or more of the remaining servers in the server pool.

Managing services relative to each other is improved by making use of the importance attribute of each server pool. Each service running in a server pool inherits the server pool's importance relative to the other server pool-hosted services in the cluster.

If the minimum size of the most important server pool is greater than zero, then the services and associated database instances in that server pool are started first on cluster startup and will be the last services and database instances running, as long as there is one server running in the cluster.

You can offer services not critical to the business in the least important server pool, ensuring that, should sufficient resources not be available due to demand or failures, those services will eventually be shut down and the more business-critical services remain available. Because many management tasks may involve making changes that can affect multiple databases, services, or server pools in a consolidated environment, you can use the evaluate mode for certain SRVCTL commands to get a report of the resource impact of a command.

Consider the following example, that evaluates the effect on the system of modifying a server pool:. As shown in the preceding example, modifying a server pool can result in many resource state changes. In Oracle Database 12 c , Oracle Clusterware supports the management of a cluster configuration policy set as a native Oracle Clusterware feature. A cluster configuration policy contains one definition for each server pool that is defined in the system.

A cluster configuration policy also specifies resource placement and cluster node availability. A cluster configuration policy set defines the names of all of the server pools that are configured in a cluster, and contains one or more configuration policies. There is always only one configuration policy in effect at any one time. However, administrators typically create several configuration policies to reflect the different business needs and demands based on calendar dates or time of day parameters.

For instance, morning hours during business days are typically when most users log in and download their email; email-related workloads are usually light at nighttime and on weekends. In such cases, you can use cluster configuration policies to define the server allocation based on the expected demand.

More specifically for this example, a configuration policy that allocates more servers to OLTP workloads is in effect during workday mornings, and another configuration policy allocates more servers to batch workloads on weekends and workday evenings. Using cluster configuration policies can also help manage clusters that comprise servers of different capabilities, such as different computer and memory sizes heterogeneous.