Then there are two cohorts: {1, 2} and {3}. 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. 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. In Oracle RAC, all the instances/servers communicate with each other using a private network. We will verify that when an equal number of database services are running on both nodes, the node with lower node number (host01) survives. Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. For storage migration, you are required to use both storage arrays by Oracle ASM temporarily. If the fast recovery area is on the source volume that is remotely mirrored, then you must also remotely mirror the flashback logs. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). A nationally recognized insurance provider in the U.S. maintains two standby databases in the same Oracle Data Guard configuration: one physical standby and one logical standby database. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. Then this process is referred as Split Brain Syndrome. Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). It also allows the storage to be laid out in a different fashion from the primary computer. Oracle Clusterware manages the availability of both the user applications and Oracle databases. 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". The processes that were once co-operating prior to the Split-Brain event occurring, independently modify the same logically shared state, thus leading to conflicting views of system state. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. They will enhance your knowledge and help you to emerge as the best candidate. 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. 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. Starting from 12.1.0.2, during split brain resolution, the new algorithm followed to decide the nodes to be evicted/retained is as follows: Fortnightly newsletters help sharpen your skills and keep you ahead, with articles, ebooks and opinion to keep you informed. This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. 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. What Is Oracle RAC. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. The premise of the Data Guard hub is that it provides higher utilization with lower cost. 008 - How Node Membership Happens in RAC? - What is Voting Disk & Split 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. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. Why is it like that? It supports bidirectional replication, data transformations, subsetting, custom apply functions, and heterogeneous platforms. At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. 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. An Oracle RAC database is connected to three instances on different nodes. For example, if the primary database fails over to one of the standby databases in the Data Guard hub, the new primary database acquires more system and storage resources while the testing resources may be temporarily starved. For example : The figure shows Oracle Database with Oracle Data Guard architecture. 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). The group(cohort) with more cluster nodes survive 1. Where two or more instances . Oracle Data Guard is designed so that it does not affect the Oracle database writer (DBWR) process that writes to data files, because anything that slows down the DBWR process affects database performance. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). Footnote2Oracle ASM automatically rebalances stored data when disks are added or removed while the database remains online. You can have up to 32 voting disks in your cluster. Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. 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. 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. The new primary database starts transmitting redo data to the new standby database. The SELECT statement is used to retrieve information from a database. split brain syndrome. 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. You might choose to use Oracle GoldenGate to configure and maintain a logical copy of your production database. To avoid splitbrain, node 2 aborted itself. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. 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. All of the business benefits of Oracle RAC. 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. Split brain syndrome in RAC - Oracle Forums You can configure Oracle GoldenGate with Oracle Data Guard to provide protection for the individual databases in the configuration. Willing to make additional provisions for remote data protection to protect against database, data, and cluster failures and corruptions. However, the online changes are not supported by SQL Apply or data capture, and therefore the effects of this subprogram are not visible on the logical standby database or replica database. What is split brain in RAC? - TheNewsIndependent Footnote1Recovery time indicated applies to database and existing connection failover. 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 of the business benefits of Oracle RAC and Oracle Data Guard. 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. 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. Split Brain Syndrome Basic Concept in Oracle RAC End-users connect to clusters through a public network. 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 . All Oracle RAC nodes can be active by implementing multiple Oracle RAC One Node configurations for different databases. 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. If it takes seconds to detect a malicious DML or DLL transaction, it typically only requires seconds to flash back the appropriate transactions. By using specialized devices, this distance can be extended to 66 kilometers. 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. These devices convert ESCON or Fibre Channel to the appropriate IP, ATM, or SONET networks. Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover). 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. Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. Oracle Enterprise Manager support for patch application simplifies software maintenance. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect. The clusters that are typical of Oracle RAC environments can provide continuous service for both planned and unplanned outages. Each site is a self-contained system. Oracle Grid Infrastructure and Oracle RAC make use of Redundant Interconnect Usage that distributes network traffic and ensures optimal communication in the cluster. 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. 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 . 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. These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. Footnote6Recovery time for human errors depend primarily on detection time. It allows you to select the table columns depending on a set of criteria. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA. Fast Recovery Area manages local recovery-related files. This architecture is referred to as an extended cluster. Oracle RAC Operational Best Practices for the Cloud Created Date: 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. The rightmost frame shows the configuration after fast-start failover has occurred. Maximum RTO for instance or node failure is in minutes. It is based on proven Oracle high availability technologies and recommendations. In Oracle RAC each node in the cluster is interconnected through a private interconnect. The figure shows users making local updates to the snapshot standby database. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. 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. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. High availability functionality to manage third-party applications, Rolling release upgrades of Oracle Clusterware. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. This book focuses primarily on the database high availability solutions. The active site is generally called the production site, and the passive site is called the standby site. This is often called the multi-master problem. 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. Clients are connected to the logical standby database and can work with its data. Oracle Net Services provide client access to the Application/Web server tier at the top of the figure, Figure 7-4 Oracle Database with Oracle RAC Architecture. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. 2. 2. Customer can designate which server(s) and resource(s) are critical 2. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. The high availability benefits to using Oracle RAC One Node include the following: Offers better database availability than traditional cold failover solutions, Provides better virtualization for databases than hypervisor-based solutions, Enables online migration of database instances and online patching and upgrading of operating system and database software (incurring no downtime), Delivers a comprehensive, single-vendor solution, with no need to implement third-party products, Is ready to scale and upgrade to multinode Oracle RAC, Provides a standardized environment and a common toolset for both single-node and multinode Oracle database deployments, Is less expensive than cold fail over solutions or a full Oracle RAC deployment. 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. Oracle Database High Availability Architectures, Choosing the Correct High Availability Architecture, Integrating Application Server High Availability, Integrating High Availability for All Applications. 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. But 1 and 2 cannot talk to 3, and vice versa. Footnote1Rolling upgrades with Oracle Clusterware and Oracle RAC incur zero downtime. 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. The basic function of a cold cluster failover is to monitor a database instance running on a server, and if a failure is detected, to restart the instance on a spare server in the cluster. If the primary database uses the asynchronous redo transport, configure your maximum data loss tolerance or the Oracle Data Guard broker's FastStartFailoverLagLimit property to meet your business requirements. 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. However, an extended cluster cannot protect against all data corruptions or specific data failures that impact the database, or against comprehensive disasters such as earthquakes, hurricanes, and regional floods that affect a greater geographical area. 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. Also, see Figure 5-2 for another example of a multiple standby database environment. host01 is evicted although it has a lower node number. b. It also gives users complete control over the routing of change records from the primary database to a replica database. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. 1. host02 is retained as it has higher number of database services executing. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. Table 7-4 shows the recovery time (including detection and client failover time) of an integrated Oracle client, whenever relevant. The term "Split-Brain" is often used to describe the scenario when two or more co-operating processes in a distributed system, typically a high availability 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 . See Oracle Data Guard Broker for a detailed description of the observer. 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. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. There are three typical causes of corruption: 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. The data is derived from actual user experiences and from Oracle service requests. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. Online Patching allows for dynamic database patching of typical diagnostic patches. As the result, 1 or more instance(s) will be evicted. Then there are two cohorts: {1, 2} and {3}. Vijay.Cherukuri-Oracle Dec 18 2011 edited Nov 5 2012. 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. Dynamic Resource Provisioning allows for dynamic system changes. . 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. Also, to prevent a full cluster outage if either site fails, the configuration includes a third voting disk on an inexpensive, low-end standard network file system (NFS) mounted device. 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. (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.). This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). 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. For example, you can put the files on different disks, volumes, file systems, and so on. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. Different character sets are required between the primary database and its replicas. Oracle Data Guard transmits redo data from the primary database to the secondary site to keep the databases synchronized. For example, for a business that has a corporate campus, the extended Oracle RAC configuration could consist of individual Oracle RAC nodes located in separate buildings. What is Voting Disk & Split Brain Syndrome in RAC Thus, when a failover occurs, you can prioritize the system resources to production activity and allocate new system resources in a grid for the standby database functions. The instances monitor each other by checking "heartbeats." High availability benefits and workload balancing outweigh performance concerns. Clusterware will evaluate cluster resources on implied workload 3. . 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. Server scalability is unlimited, and if applications grow to require more resources than a single node can supply, you can perform an online upgrade to a traditional multinode Oracle RAC configuration. New requests are accepted after the Split-Brain event and then performed on potentially corrupted system state (thus potentially corrupting system state even further). 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. See Section 7.1.3, "Oracle Database with Oracle RAC One Node" for more information. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. Oracle GoldenGate can capture changes at a source database, and the captured changes can be propagated asynchronously to replica databases. Better resilience and data protectionOracle Data Guard ensures much better data protection and data resilience than remote mirroring solutions. Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. Footnote2The portion of any application connected to the failed system is temporarily affected. See Section 7.2 for a comparison of the different architectures and highlights of the benefits and considerations. 3. Oracle Database with Oracle RAC on Extended Clusters. Oracle Clusterware cold cluster failover combined with Oracle Data Guard makes a tightly integrated solution in which failover to the secondary node in the cold cluster failover is transparent and does not require you to reconfigure the Oracle Data Guard environment or perform additional steps. 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 . 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. The center frame shows the configuration during fast-start failover. Many high availability architectures today use clusters alone to provide some rudimentary node redundancy and automatic node failover. During the process of resolving conflicts, information may be lost or become corrupted. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. Higher ROIBusinesses must obtain maximum value from their IT investments, and ensure that no IT infrastructure is sitting idle.
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