There are three typical causes of corruption: Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. Oracle Data Guard transmits redo data from the primary database to the secondary site to keep the databases synchronized. Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. 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. Communication among the nodes is optimized by means of Redundant Interconnect Usage (without requiring the use of bonding or other technologies) to provide stability, reliability, and scalability. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. Better suited for WANsRemote mirroring solutions based on storage systems often have a distance limitation due to the underlying communication technology (Fibre Channel or ESCON (Enterprise Systems Connection)) used by the storage systems. A global provider of information services to legal and financial institutions uses multiple standby databases in the same Oracle Data Guard configuration to minimize downtime during major database upgrades and platform migrations. For logical standby databases, this solution: Provides the simplest form of one-way logical replication, Allows for structural changes to the standby database, such as changes to local tables, adding schemas, indexes, and materialized views, Off-loads production by providing read-only access to a synchronized standby database and allows read/write access to local tables that are not being modified by the primary database, All of the business benefits of Oracle Clusterware (cold cluster failover) and Oracle Data Guard. Although both types of solutions provide high availability, active-active solutions generally offer higher scalability and faster failover, although they tend to be more expensive. Also, for large data centers with a need to support many applications with Oracle Data Guard requirements, you can build an Oracle Data Guard hub to reduce the total cost of ownership. Split Brain Syndrome, In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. After you have chosen an architecture, then implement it using the operational and configuration best practices described in the MAA white papers and in Oracle Database High Availability Best Practices. 1. This has the potential for data corruption. Table 7-3 identifies the additional capabilities provided by the architectures that build on Oracle Database and attempts to label each architecture with its greatest strengths. 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. We will verify that when an unequal number of database services are running on the two nodes, the node hosting the higher number of database services survives even if it has a higher node number. By reducing the combinations of software that you must coordinate and support, you can increase the manageability and availability of your system software. Compared to mirroring, Oracle Data Guard provides better performance and is more efficient, Oracle Data Guard always verifies the state of the standby database and validates the data before applying redo data, and Oracle Data Guard enables you to use the standby database for updates while it protects the primary database. Oracle Data Guard is designed to allow businesses get something useful out of their expensive investment in a disaster-recovery site. Start both the services for database admindb so that equal number of database services execute on both the nodes. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. Then this process is referred as Split Brain Syndrome. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. During normal operation, the production site services requests; in the event of a site failover or switchover, the standby site takes over the production role and all requests are routed to that site. The split brain syndrome and its affects and how it has been managed in oracle is mentioned below. The Oracle Application Server High Availability Guide describes the following high availability services in Oracle Application Server in detail: Process death detection and automatic restart. 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. The goal of the MAA is to remove the complexity in designing the optimal high availability architecture by providing configuration recommendations and tuning tips to optimize your architecture and Oracle features. Suppose there are 3 nodes in the following situation. When the instance members in a RAC fail to ping/connect to each other via this private network and continue to process data block independently. Oracle RAC Split Brain Syndrome Scenerio. Node Weighting for Split Brain Resolution Without better understanding of what is critical or of higher priority to the customer's workload, Oracle Clusterware has always resolved split brain conditions in favor of the cluster cohort containing the node with the lowest node number (i.e. As the result, 1 or more instance(s) will be evicted. Willing to make additional provisions for remote data protection to protect against database, data, and cluster failures and corruptions. A logical copy configured and maintained using Oracle GoldenGate is called a replica, not a logical standby database, because it provides many capabilities that are beyond the scope of the normal definition of a standby database. Oblivious of the existence of other cluster fragments, each sub-cluster continues to operate independently of the others. Oracle Data Guard provides a compelling set of technical and business reasons that justify its adoption as the disaster recovery and data protection technology of choice, over traditional remote mirroring solutions. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. Providing application-specific failure detection means Oracle Clusterware can fail over not only during the obvious cases such as when the instance is down, but also in the cases when, for example, an application query is not meeting a particular service level. In previous releases, technologies like bonding or trunking were used to make use of redundant networks for the interconnect. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). See Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)" for more information about the best practices documentation. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. Footnote1Rolling upgrades with Oracle Clusterware and Oracle RAC incur zero downtime. Recovery Manager (RMAN) optimizes local repair of data failures. Oracle Data Guard Advantages Over Traditional Solutions. Node 1 is connected to Node 2 and to the Oracle database, but Node 1 is currently idle, in standby mode. This would lead to collision and corruption of shared data as each sub-cluster assumes ownership of shared data. Several standby databases in an Oracle RAC environment residing in a cluster of servers, called a grid server. If you configure a single voting disk, then you should use external mirroring to provide redundancy. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. A highly available and resilient application requires that every component of the application must tolerate failures and changes. The application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). The rightmost frame shows the configuration after fast-start failover has occurred. The center frame shows the configuration during fast-start failover. Where two or more instances . If your VM is sized too small, you can migrate the Oracle RAC One instance to another larger Oracle VM node in the cluster (using the online database relocation utility) or move the Oracle RAC One instance to another Oracle VM node, and then resize the Oracle VM. Rolling upgrade for system, clusterware, database, and operating system. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. The figure shows users making local updates to the snapshot standby database. 2. 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. the number of database services executing on a node. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle One Node database. For example, Table 7-1 provides some insight into the probability of different outages during unplanned and planned activities. Different character sets are required between the primary database and its replicas. For more information about constructing multiple-source replication environments, see the Oracle GoldenGate documentation. Support is for single-instance databases only. Then there are two cohorts: {1, 2} and {3}. b. With Oracle Clusterware, you also define an application VIP so that users can access the application independently of the node in the cluster where the application is running. Oracle recommends that you create and store the local backups in the fast recovery area. For example: Active Data Guard, Redo Apply for physical standby databases, and SQL Apply for logical standby databases, multiple protection modes, push-button automated switchover and failover capabilities, automatic gap detection and resolution, GUI-driven management and monitoring framework, cascaded redo log destinations. Oracle Automatic Storage Management and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and utilization. An Oracle RAC database is connected to three instances on different nodes. The servers on which you want to run Oracle Clusterware must be running the same operating system. Split Brain Syndrome in RAC. Fast-start failover is recommended to provide automatic failover without user intervention and bounded recovery time. Why is it like that? A telecommunications provider uses asynchronous redo transport to synchronize a primary database on the West Cost of the United States, with a standby database on the East Coast, over 3,000 miles away. Split Brain Resolution in Oracle Clusterware 12c Rel 2 1. It also allows the storage to be laid out in a different fashion from the primary computer. It requires only a standard TCP/IP-based network link between the two computers. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover. Then this process is referred as Split Brain Syndrome. Clusterware will evaluate cluster resources on implied workload 3. . . Oracle Application Server provides redundancy by offering support for multiple instances supporting the same workload. These figures show how you can use the Oracle Clusterware framework to make both Oracle Database and your custom applications highly available. In the figure, Node 2 is now the active instance connected to the Oracle database and servicing applications and users. This is because corruptions introduced on the production database probably can be mirrored by remote mirroring solutions to the standby site, but corruptions are eliminated by Oracle Data Guard. Split Brain Condition occurs when a single cluster has a failure that results in reconfiguration of cluster into multiple partitions, with each partition forming its own sub-cluster without the knowledge of the existence of other. 2. The premise of the Data Guard hub is that it provides higher utilization with lower cost. Hi Guru's. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). the clusterware identifies the largest sub-cluster, and aborts all the nodes which do NOT belong to that sub-cluster. Fast Recovery Area manages local recovery-related files. which node first joined the cluster). Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect. This architecture is identical to the single-standby database architecture that was described in Section 7.1.5.1, except that there are multiple standby databases in the same Oracle Data Guard configuration. Oracle Data Guard is a high availability and disaster-recovery solution that provides very fast automatic failover (referred to as fast-start failover) in database failures, node failures, corruption, and media failures. Table 7-2 High Availability Architecture Recommendations. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. Footnote1Applications (or a portion of an application) connected to the system that is being maintained may be temporarily affected. Site configurations are on heterogeneous platforms. the. In a non-RAC Oracle database, a single instance accesses a single database. Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. Many high availability architectures today use clusters alone to provide some rudimentary node redundancy and automatic node failover. If the observer is unable to regain a connection to the primary database within the specified time, and the target standby database is ready for fast-start failover, then fast-start failover ensues. Figure 7-7 Oracle Database with Oracle Data Guard on Primary and Multiple Standby Sites, Oracle Data Guard Concepts and Administration for more information about the various types of standby databases and to find out what data types are supported by logical standby databases, Oracle Database High Availability Best Practices for configuration best practices, The "Managing Data Guard Configurations Having Multiple Standby Databases - Best Practices" white paper, and other Oracle Data Guard white papers at. You should determine if both sites are likely to be affected by the same disaster. Dynamic Resource Provisioning allows for dynamic system changes. SELECT statements might be as straightforward as selecting a few . Oracle GoldenGate is optimized for replicating data. The figure shows Oracle Database with Oracle Data Guard architecture. The figure shows the same Oracle Data Guard configuration in three different frames, as described in the following list: The leftmost frame shows the configuration before fast-start failover occurs. Corruption Prevention, Detection, and Repair detect and prevent some corruptions and lost writes. Oracle RAC One Node provides relocation of Oracle RAC primary and standby databases configured with Oracle Data Guard (This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2)). Oracle Grid Infrastructure and Oracle RAC make use of Redundant Interconnect Usage that distributes network traffic and ensures optimal communication in the cluster. 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. Network connection changes and other site-specific failover activities may lengthen overall recovery time. If it takes seconds to detect a malicious DML or DLL transaction, it typically only requires seconds to flash back the appropriate transactions. Nodes 1,2 can talk to each other. For example, you can put the files on different disks, volumes, file systems, and so on. See the high availability solutions and recommendations for Oracle Application Server, Oracle Enterprise Manager, and Oracle Applications on the MAA Web site at: Oracle Database High Availability Best Practices, Oracle Real Application Clusters Administration and Deployment Guide, Oracle Data Guard Concepts and Administration, Oracle Streams Replication Administrator's Guide, Oracle Fusion Middleware High Availability Guide, Oracle Application Server High Availability Guide, Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)", Corruption Prevention, Detection, and Repair, Online Application Maintenance and Upgrades, Description of "Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance", Section 7.1.3, "Oracle Database with Oracle RAC One Node", Description of "Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover)", Description of "Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover)", Description of "Figure 7-4 Oracle Database with Oracle RAC Architecture", Description of "Figure 7-5 Oracle RAC Extended Cluster", http://www.oracle.com/technetwork/database/clustering/overview/, Description of "Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover", Description of "Figure 7-7 Oracle Database with Oracle Data Guard on Primary and Multiple Standby Sites", Description of "Figure 7-8 Oracle Clusterware (Cold Cluster Failover) and Oracle Data Guard", Description of "Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA". But i want to test it on a test environment in my view for that i need to fail or make the node's to lose connectivity with one another but then continue to operate independently of each other. Prior to Oracle Database 12.1.0.2c, the algorithm to determine the node (s) to be retained / evicted is as follows: If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster . Split Brain: Whats new in Oracle Database 12.1.0.2c? The cold cluster failover solution with Oracle Clusterware provides these additional advantages over a basic database architecture: Automatic recovery of node and instance failures in minutes, Automatic notification and reconnection of Oracle integrated clientsFoot3, Ability to customize the failure detection mechanism. This architecture is referred to as an extended cluster. The SELECT statement is used to retrieve information from a database. The instances monitor each other by checking "heartbeats." Footnote3For qualified one-off patches only. Upon detecting the break in communication, the observer attempts to reestablish a connection with the primary database for the amount of time defined by the FastStartFailoverThreshold property before initiating a fast-start failover. 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. Now talking about split-brain concept with respect to oracle . Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect, Although the servers are physically up and running and the database instances on these servers is also running. It also gives users complete control over the routing of change records from the primary database to a replica database. As per Split brain syndrome in Oracle RAC in case of inter-connect failures the master node will evict other/dead nodes . An exception is undropping a table, which is literally instantaneous regardless of detection time. Provides the simplicity of a physical replica. Maximum RTO for instance or node failure is in minutes. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. The following list describes examples of Oracle Data Guard configurations using single standby databases: A national energy company uses a standby database located in a separate facility 10 miles away from its primary data center. The production database is connected over the network to the physical standby database site and the logical standby database site (the standby databases may be at the same or different sites). Oracle Secure Backup provides a centralized tape backup management solution. Better functionalityOracle Data Guard provides full suite of data protection features that provide a much more comprehensive and effective solution optimized for data protection and disaster recovery than remote mirroring solutions. They will enhance your knowledge and help you to emerge as the best candidate. Nodes 1,2 can talk to each other. To protect against site failures, the MAA recommends that Oracle RAC and Oracle Data Guard reside on separate systems (clusters) and data centers. Section 3.4.1 describes how Oracle Clusterware is software that, when installed on servers running the same operating system, enables the servers to be bound together to operate as if they are one server, and manages the availability of user applications and Oracle databases. These updates are discarded when the snapshot database is reconverted to a physical standby database. More investment and expertise to build and maintain an integrated high availability solution is available. The key factors include: Recovery time objective (RTO) and recovery point objective (RPO) for unplanned outages and planned maintenance, Total cost of ownership (TCO) and return on investment (ROI). Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). Limited support for mixed platforms. Provides maximum protection from physical corruptions. 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. The common voting result will be: a. 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. Oracle Security Features prevent unauthorized access and changes. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. What Is Oracle RAC. There is no fancy or expensive hardware required. Oracle Database with Oracle RAC on Extended Clusters. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. 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.
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