More investment and expertise to build and maintain an integrated high availability solution is available. To ensure data consistency, each instance of a RAC database needs to keep heartbeat with the other instances. Traditionally, Oracle RAC is used in a multinode architecture, with many separate database instances running on separate servers. The center frame shows the configuration during fast-start failover. Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). The system resources can be dynamically allocated and deallocated depending on various priorities. If the sub-clusters have unequal node weights, the sub-cluster having the higher weight survives so that, in a 2-node cluster, the node with the lowest node number might be evicted if it has a lower weight. With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. The active site is generally called the production site, and the passive site is called the standby site. Oracle Data Guard is designed to allow businesses get something useful out of their expensive investment in a disaster-recovery site. But 1 and 2 cannot talk to 3, and vice versa. An Oracle RAC extended cluster is an architecture that provides extremely fast recovery from a site failure and allows for all nodes, at all sites, to actively process transactions as part of single database cluster. When a node is physically up and running and database instances are also running fine, but private interconnect fails between two or more nodes and an . I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). Where two or more instances . When a node is physically up and running and database instances are also running fine, but private interconnect fails between two or more nodes and an instance member fails to connect or ping to one . Database scalability beyond one instance or node. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. In simple terms "Split brain" means that there are 2 or more distinct sets of nodes, or "cohorts", with no communication between the two cohorts. Includes all of the features required for cluster management, including node membership, group services, global resource management, and high availability functions such as managing third-party applications, event management, and Oracle notification services that enable Oracle clients to reconnect to the new primary database after a failure. Oracle Automatic Storage Management and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and utilization. Let say 2 node RAC configuration node 1 is defined as master node (by some parameter like load and others) incase of network failures node 1 will terminate node 2 . Oracle Enterprise Manager support for patch application simplifies software maintenance. You can configure the failed application connections to fail over to the replica. Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. This is called Split Brain. Oracle Data Guard provides more comprehensive data protection and its more efficient network usage allows plenty of room to grow without the expense of upgrading its network. However, when the data centers are located more than 66 kilometers apart, you must use a series of repeaters and converters from third-party vendors. An infrastructure services provider to the telecommunication industry uses a single standby database located over 400 miles away from the primary database configured for synchronous redo transport, enabling zero-data-loss failover for maximum data protection and high availability. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. Additional protection from data center failure with special considerations that are documented in Section 7.1.4.1, Highest level of availability for server or computer room failure. Maximum RTO for instance or node failure is in seconds. The following sections provide an overview of Oracle Database high availability architectures and implement the MAA best practices: Oracle Database with Oracle Clusterware (Cold Cluster Failover), Oracle Database with Oracle Real Application Clusters (Oracle RAC), Oracle Database with Oracle Clusterware and Oracle Data Guard, Oracle Database with Oracle RAC One Node and Oracle Data Guard, Oracle Database with Oracle RAC and Oracle Data Guard. The database consists of a collection of data files, control files, and redo logs located on disk. The fast-start failover has completed and the target standby database is running in the primary database role. Common messages in instance alert log are similar to: In above example, instance 2 LMD0 (pid 29940) is the receiver in IPC Send timeout. For physical standby databases, this solution: Supports very high primary database throughput. With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. They will enhance your knowledge and help you to emerge as the best candidate. Typically, this is not possible with remote mirroring solutions. Simulate loss of connectivity between two nodes. Nodes 1,2 can talk to each other. Network connection changes and other site-specific failover activities may lengthen overall recovery time. Oracle RAC on an extended cluster provides greater availability than a local Oracle RAC cluster, but an extended cluster may not completely fulfill the disaster recovery requirements of your organization. Thus, we observed that when unequal number of database services are running on the two nodes, the node with higher number of database services survives even though it has a higher node number. You can define multiple application VIPs, with generally one application VIP defined for each application running. (The application server on the secondary site can be active and processing client requests such as queries if the standby database is a physical standby database with the Active Data Guard option enabled, or if it is a logical standby database.). Consider using Oracle Database with Oracle GoldenGate if one or more of the following conditions are true: Updates are required on both sites or databases, and the changes must be propagated bidirectionally. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. An exception is undropping a table, which is literally instantaneous regardless of detection time. In a "split brain" situation, voting disk is used to determine which node (s) will survive and which node (s) will be evicted. Oracle recommends that you use the following Oracle features to make a standalone database on a single computer available for certain failures and planned maintenance activities: Fast-Start Fault Recovery bounds and optimizes instance and database recovery times. Starting in Oracle Database 12.1.0.2c, the new algorithm to determine the node(s) to be retained / evicted is as follows: Now I will demonstrate this new feature in an Oracle 12.1.0.2c standard 3 node cluster, using an RAC database called admindb for one of the possible factors contributing to the node weight, i.e. If all the sub-clusters are of the same size, the functionality has been modified as: If the sub-clusters have equal node weights, the sub-cluster with the lowest numbered node in it survives so that, in a 2-node cluster, the node with the lowest node number will survive. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. Oracle Database with Oracle RAC on Extended Clusters. As the result, 1 or more instance(s) will be evicted. Oracle Restart enhances the availability of Oracle databases, listeners, and Oracle ASM instances in a single-instance environment by monitoring and automatically restarting Oracle processes. See Section 7.2 for a comparison of the different architectures and highlights of the benefits and considerations. You might choose to use Oracle GoldenGate to configure and maintain a logical copy of your production database. Split Brain: Whats new in Oracle Database 12.1.0.2c? What Is Oracle RAC. For example, you can put the files on different disks, volumes, file systems, and so on. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. Maximum RTO for instance or node failure is in minutes. Oracle Application Server provides high availability and disaster recovery solutions for maximum protection against any kind of failure with flexible installation, deployment, and security options. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. Oracle GoldenGate is optimized for replicating data. Recovery Manager optimizes local repair of data failures using local backups. Split Brain Syndrome Basic Concept in Oracle RAC. If it takes seconds to detect a malicious DML or DLL transaction, it typically only requires seconds to flash back the appropriate transactions. The split brain syndrome and its affects and how it has been managed in oracle is mentioned below. Oracle GoldenGate can capture changes at a source database, and the captured changes can be propagated asynchronously to replica databases. End-users connect to clusters through a public network. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. Note, however, that the synchronous redo transport does not impose any physical distance limitation. Run-time performance level management with Oracle Database Quality of Service Management (This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2)), Zero downtime with Grid Control provisioning, Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patchesFoot1, Database Grid with site failure protection, Simplest high availability, data protection, and disaster-recovery solution, Automatic and fast failover for computer failure, storage failure, data corruption, for configured ORA- errors or conditions and database failures, Rolling upgrade for system, clusterware, database, and operating systemFoot2, Ability to off-load backups to the standby database, Ability to off-load read and reporting workload to the standby database. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. the number of database services executing on a node. which node first joined the cluster). The figure shows users making local updates to the snapshot standby database. The group(cohort) with lower node member survive, in case of same number of node(s) available in each group. Although traditional solutions (such as backup and recovery from tape, storage-based remote mirroring, and database log shipping) can deliver some level of high availability, Oracle Data Guard provides the most comprehensive high availability and disaster recovery solution for Oracle databases. A highly available application must analyze every component that affects the application, including the network topology, application server, application flow and design, systems, and the database configuration and architecture. For more information, see "Data Guard Support for Heterogeneous Primary and Physical Standbys in Same Data Guard Configuration" in My Oracle Support Note at, https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&id=413484.1. Support for heterogeneous platforms, versions, and character sets. Footnote2Rolling upgrades with Oracle Data Guard incur minimal downtime. These best practices are required to maximize the benefits of each architecture. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. RAC Split Brain Syndrome. Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. Figure 7-5 shows an Oracle RAC extended cluster for a configuration that has multiple active instances on six nodes at two different locations: three nodes at Site A and three at Site B. For example, an Oracle Data Guard hub could include multiple databases and applications that are supported in a grid server and storage architecture. It is possible, under certain circumstances, to build and deploy an Oracle RAC system where the nodes in the cluster are separated by greater distances. Check that only two nodes (host01 and host02) are active and host01 has lower node number, Create two singleton services for the RAC database admindb. Applications scale in an Oracle RAC environment to meet increasing data processing demands without changing the application code.

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