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. Split brain syndrome in RAC - Oracle Forums Oracle Data Guard Advantages Over Traditional Solutions. For data resident in Oracle databases, Oracle Data Guard, with its built-in zero-data-loss capability, is more efficient, less expensive, and better optimized for data protection and disaster recovery than traditional remote mirroring solutions. The voting result is similar to clusterware voting result. Online Reorganization and Redefinition allows for dynamic data changes. The sum of benefits of Oracle Clusterware with Oracle Data Guard, Best high availability, data protection, and disaster-recovery solution with scalability built in, The sum of benefits of Oracle RAC with Oracle Data Guard, Oracle Database with Oracle GoldenGateFoot3, Bidirectional replication and information management, Replica database (or databases) available for read/write use, Fast failover for computer failure and storage failure, Minimum downtime for computer or site maintenance and database and application upgrades. Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). Automatic block repair may be possible, thus eliminating any downtime in an Oracle Data Guard configuration. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. Clusterware will evaluate cluster resources on implied workload 3. . Network connection changes and other site-specific failover activities may lengthen overall recovery time. For example, you can put the files on different disks, volumes, file systems, and so on. Whatever the case, these Oracle RAC interview questions and answers are for you. For storage migration, you are required to use both storage arrays by Oracle ASM temporarily. Footnote1Recovery time indicated applies to database and existing connection failover. CSSD process in each RAC node maintains a heart beat in a block of size 1 OS block in a specific offset by read/write system calls (pread/pwrite), in the voting disk. Oracle recommends that you use automatic undo management with sufficient space to attain your desired undo retention guarantee, enable Oracle Flashback Database, and allocate sufficient space and I/O bandwidth in the fast recovery area. This chapter describes the various high availability architectures in an Oracle environment and helps you to choose the correct architecture for your organization. Oracle Data Guard transmits redo data from the primary database to the secondary site to keep the databases synchronized. This would lead to collision and corruption of shared data as each sub-cluster assumes ownership of shared data. 3. 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. At a high level, Oracle Application Server local high availability architectures include several active-active and active-passive architectures for the OracleAS middle-tier and the OracleAS Infrastructure. An architecture that combines Oracle Database with Oracle RAC is inherently a highly available system. The center frame shows the configuration during fast-start failover. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. Rolling upgrade for system, clusterware, operating system, database, and application. If the primary system should fail, the first standby database becomes the new primary database. See Section 7.1.3, "Oracle Database with Oracle RAC One Node" for more information. Footnote7Recovery time depends on block media recovery and the time it takes to restore a consistent block from the flashback logs or database backups, and to recover the block by applying all the redo from archive logs and online redo logs. The probability of failing over all databases at the same time is unlikely. Since I will only explore the scenarios for which functionality has been modified, i.e. 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 Secure Backup provides a centralized tape backup management solution. 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. However, when you use Oracle Clusterware, there is no need or advantage to using third-party clusterware. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. 12) Mention what is split brain syndrome in RAC? Outages or data loss that could affect customer service and safety are avoided by using Oracle Data Guard synchronous transport and automatic failover (fast-start failover). pagespeed.lazyLoadImages.overrideAttributeFunctions(); You should determine if both sites are likely to be affected by the same disaster. Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). Several standby databases in an Oracle RAC environment residing in a cluster of servers, called a grid server. Oracle Database with Oracle RAC on Extended Clusters. Fine control of information and data sharing are required. 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. Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. 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 Automatic Storage Management and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and utilization. Oracle RAC Split Brain Syndrome Scenerio. Provides maximum protection from physical corruptions. The instances monitor each other by checking "heartbeats." Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. Applications scale in an Oracle RAC environment to meet increasing data processing demands without changing the application code. In the figure, the configuration is operating in normal mode in which Node 1 is the active instance connected to Oracle Database that is servicing applications and users. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. 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. Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. 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. This is often called the multi-master problem. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. 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. For physical standby databases, this solution: Supports very high primary database throughput. Footnote2Rolling upgrades with Oracle Data Guard incur minimal downtime. 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. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. For high availability, Oracle recommends that you have a minimum of three voting disks. Oracle Flashback Technology optimizes logical failure repair. Maximum RTO for instance or node failure is in seconds. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. 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. What is Voting Disk & Split Brain Syndrome in RAC 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. Then this process is referred as Split Brain Syndrome. A highly available and resilient application requires that every component of the application must tolerate failures and changes. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. Oracle GoldenGate can capture data changes at the primary database or downstream at a replica database, thus enabling users to build hub-and-spoke network configurations that can support hundreds of replica databases. 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. 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. 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. There are some corruptions that cannot be addressed by automatic block repair, and for those we can rely on Data Guard failover that takes seconds to minutes. When a database is started, Oracle Database allocates a memory area called the System Global Area (SGA) and starts one or more Oracle Database processes. This figure shows Oracle Database with Oracle RAC architecture for a partitioned three-node database. Where two or more instances . The figure shows Oracle Database with Oracle Data Guard architecture. Support for heterogeneous platforms, versions, and character sets. In addition to maintaining its own disk block, CSSD processes also monitors the disk blocks maintained by the CSSD processes running in other cluster nodes. But 1 and 2 cannot talk to 3, and vice versa. What is split brain in Oracle RAC? 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. At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. From the entry point to an Oracle Application Server system (content cache) to the back-end layer (data sources), all the tiers that are crossed by a request can be configured in a redundant manner with Oracle Application Server. Footnote6Recovery time for human errors depend primarily on detection time. PDF Oracle Clusterware 12c Release 2 Technical Overview Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. These solutions are categorized into local high availability solutions that provide high availability in a single data center deployment, and disaster-recovery solutions, which are usually geographically distributed deployments that protect your applications from disasters such as floods or regional network outages. 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". Oracle Data Guard is operating in a steady state, with the primary database transmitting redo data to the target standby database and the observer monitoring the state of the entire configuration. As a result, equal number of database services execute on both the nodes. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. In order to make largest number of resources available to the users, the node weight is computed for each node based on number of the resource executing on it and the sub-cluster with higher weight will survive. host01 is retained as it has a lower node number. 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. Network addresses are failed over to the backup node. 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. All of the business benefits of Oracle RAC. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. At the snapshot standby database redo data is received, but it is not applied until the snapshot standby database is reconverted to a physical standby database. Oracle RAC Interview Questions - Coherence and Split-Brain By reducing the combinations of software that you must coordinate and support, you can increase the manageability and availability of your system software. The individual nodes are running fine and can accept user connections and work . You should adopt the MAA best practices to achieve the optimal recovery time and configuration. See Oracle Data Guard Broker for a detailed description of the observer. In Oracle RAC, all the instances/servers communicate with each other using a private network. When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. It also allows the storage to be laid out in a different fashion from the primary computer. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability, Automatic and fast failover for computer failure, Minimum rolling upgrade capabilities for system, clusterware, and operating systemFootref1, High availability, scalability, and foundation of server database grids, Automatic recovery of failed nodes and instances, Fast application notification (FAN) with integrated Oracle client failover, FAN with integrated Oracle client failover for pooled resources and third-party vendor middle tiers. Split brain scenario - RAC and PXC. Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. 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.