For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. (adsbygoogle=window.adsbygoogle||[]).push({}); Split Brain is often used to describe the scenario when two or more nodes in a cluster, lose connectivity with one another but then continue to operate independently of each other, including acquiring logical or physical resources, under the incorrect assumption that the other process(es) are no longer operational or using the said resources. This figure shows Oracle Database with Oracle RAC architecture for a partitioned three-node database. Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Evaluate logical standby databases if additional indexes are required for reporting purposes and if your application only uses data types supported by logical standby database and SQL Apply. Split Brain: Whats new in Oracle Database 12.1.0.2c? pagespeed.lazyLoadImages.overrideAttributeFunctions(); Footnote1Rolling upgrades with Oracle Clusterware and Oracle RAC incur zero downtime. Because Oracle Data Guard only propagates the redo data in the logs, and the log file consistency is checked before it is applied, all such external corruptions are eliminated by Oracle Data Guard. High availability solution with added data and disaster recovery protection. Each instance is associated with a service: HR, Sales, and Call Center. You should determine if both sites are likely to be affected by the same disaster. Oracle Flashback Technology optimizes logical failure repair. A single standby database architecture consists of the following key traits and recommendations: Standby database resides in Site B. To ensure data consistency, each instance of a RAC database needs to keep heartbeat with the other instances. Oracle Application Server instances can be installed in either site as long as they do not interfere with the instances in the disaster recovery setup. the. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. Footnote3For qualified one-off patches only. Why is it like that? Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. 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: Verify that admindb is the only database in the cluster having its instances executing on host01 and host02. These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. Applications can easily mask failures to the end user. All Oracle RAC nodes can be active by implementing multiple Oracle RAC One Node configurations for different databases. Figure 7-8 Oracle Clusterware (Cold Cluster Failover) and Oracle Data Guard, The application servers on the secondary site are connected to the WAN traffic manager by a dotted line to indicate that they are not actively processing client requests at this time. For high availability, Oracle recommends that you have a minimum of three voting disks. 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. Logical or user failures that manipulate logical data (DMLs and DDLs). Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. 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. The configuration can be an active-active configuration using Oracle Application Server Cluster or an active-passive configuration using Oracle Application Server Cold Cluster Failover. When the two data centers are located relatively close to each other, extended clusters can provide great protection for some disasters, but not all. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. A highly available and resilient application requires that every component of the application must tolerate failures and changes. For example, if the extended cluster configuration is set up properly, it can protect against disasters such as a local power outage, an airplane crash, or a flooded server room. This is called Split Brain. 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. 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. 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. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. Prior to Oracle Database 12.1.0.2c, the algorithm to determine the node(s) to be retained / evicted is as follows: However, starting from 12.1.0.2c, in case of split brain, some improvement has been made to node eviction algorithm. Online Reorganization and Redefinition allows for dynamic data changes. A global manufacturing company used Oracle Data Guard to replace storage-based remote mirroring and maintain a standby database at its recovery site 50 miles away from the primary site. 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. 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. Split Brain Syndrome: In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. Oracle Grid Infrastructure and Oracle RAC make use of Redundant Interconnect Usage that distributes network traffic and ensures optimal communication in the cluster. The servers on which you want to run Oracle Clusterware must be running the same operating system. This section summarizes the advantages of the different high availability architectures and provides guidelines for you to choose the correct high availability architecture for your business. For example : This architecture is referred to as an extended cluster. Online Patching allows for dynamic database patching of typical diagnostic patches. 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 . For virtualization, Oracle RAC One Node with Oracle VM increases the benefit of Oracle VM with the high availability and scalability of Oracle RAC. You can have up to 32 voting disks in your cluster. Maximum RTO for instance or node failure is in seconds to minutes. . Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. 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. The voting result is similar to clusterware voting result. Where two or more instances . Fast Recovery Area manages local recovery-related files. The combination of Oracle RAC and Oracle Data Guard provide the most comprehensive architecture for reducing downtime for scheduled outages and preventing, detecting, and recovering from unscheduled outages. For example, an Oracle Data Guard hub could include multiple databases and applications that are supported in a grid server and storage architecture. Table 7-3 Additional Capabilities of High Level Oracle High Availability Architectures, The foundation for all high availability architectures. When two or more nodes fail to ping or connect to each other via this private interconnect, theclustergets partitionedinto two or more smaller sub-clusters each of which cannot talk to others over the interconnect. To maintain the standby site for failover, not only must the standby site contain homogeneous installations and applications, data and configurations must also be synchronized constantly from the production site to the standby site. Rolling upgrades for system and hardware changes, Rolling patch upgrades for some interim patches, security patches, CPUs, and cluster software, Fast, automatic, and intelligent connection and service relocation and failover, Comprehensive manageability integrating database and cluster features with Grid Plug and Play and policy-based cluster and capacity management, Load balancing advisory and run-time connection load balancing help redirect and balance work across the appropriate resources. To avoid splitbrain, node 2 aborted itself. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. If it takes seconds to detect a malicious DML or DLL transaction, it typically only requires seconds to flash back the appropriate transactions. Uses a private network and voting disk-based communication to detect and resolve split-brain Foot 2 scenarios. Oracle Application Server provides redundancy by offering support for multiple instances supporting the same workload. Oracle Enterprise Manager support for patch application simplifies software maintenance. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. However, when you use Oracle Clusterware, there is no need or advantage to using third-party clusterware. With Database Server Grid and Database Storage Grid (described in Section 5.2 and Section 5.3), you can build standby database and testing hubs that use a pool of system resources. Better resilience and data protectionOracle Data Guard ensures much better data protection and data resilience than remote mirroring solutions. Provides seamless integration with, and migration to, Oracle Real Application Clusters (Oracle RAC) and Oracle Data Guard. If the node running your Oracle RAC One Node becomes overloaded, you can relocate the instance to another node in the cluster using the online database relocation utility (srvctl relocate database), with no downtime for application users. Flexible propagation and management of data, transactions, and events. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. Provides maximum protection from physical corruptions. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. The figure shows Oracle Database with Oracle Data Guard architecture. With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. Oracle Quality of Service (QoS) Management for policy-based run-time management of resource allocation to database workloads to ensure service levels are met in order of business need under dynamic conditions. The instances monitor each other by checking "heartbeats." The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. This book focuses primarily on the database high availability solutions. 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. host02 is retained as it has higher number of database services executing. Clusterware will evaluate cluster resources on implied workload 3. . If all the sub-clusters are of the same size, the sub-cluster having the lowest numbered node survives so that, in a 2-node cluster, the node with the lowest node number will survive. 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. 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. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. Footnote2Rolling upgrades with Oracle Data Guard incur minimal downtime. If the fast recovery area is on the source volume that is remotely mirrored, then you must also remotely mirror the flashback logs. 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. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. 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. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. You can configure the failed application connections to fail over to the replica. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. Section 7.1.8 describes how you can achieve the highest level of availability with Oracle RAC and Oracle Data Guard. The logical standby database may contain additional indexes and materialized views. By using specialized devices, this distance can be extended to 66 kilometers. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. These best practices are required to maximize the benefits of each architecture. Vijay.Cherukuri-Oracle Dec 18 2011 edited Nov 5 2012. Then this process is referred as Split Brain Syndrome. 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. Simulate loss of connectivity between two nodes. You can define multiple application VIPs, with generally one application VIP defined for each application running. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. If the sub-clusters are of the different sizes, the functionality is same as earlier i.e. Many high availability architectures today use clusters alone to provide some rudimentary node redundancy and automatic node failover. Maximum RTO for instance or node failure is in seconds. When you move the Oracle RAC One Node instance to the newly resized Oracle VM node, you can dynamically increase any limits programmed with Resource Manager Instance Caging. host01 is evicted although it has a lower node number. Then there are two cohorts: {1, 2} and {3}. RAC Split Brain Syndrome. Site configurations are on heterogeneous platforms. The recommended high availability and disaster-recovery architectures that use Oracle Data Guard are described in the following sections: Overview of Single Standby Database Architectures, Overview of Multiple Standby Database Architectures. In addition, allowing maintenance operations to occur on a subset of components in the cluster while the application continues to run on the rest of the cluster can reduce planned downtime. Oracle Database with Oracle RAC on Extended Clusters. The following list describes examples of Oracle Data Guard configurations using multiple standby databases: A world-recognized financial institution uses two remote physical standby databases for continuous data protection after failover. 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. An Oracle RAC database is connected to three instances on different nodes. (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.). 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 .
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