what is split brain in oracle rac

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. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. More investment and expertise to build and maintain an integrated high availability solution is available. Support for heterogeneous platforms, versions, and character sets. Footnote3For qualified one-off patches only. The logical standby database may contain additional indexes and materialized views. When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. Better resilience and data protectionOracle Data Guard ensures much better data protection and data resilience than remote mirroring solutions. Another possible configuration might be a testing hub consisting of snapshot standby databases. The probability of failing over all databases at the same time is unlikely. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. Oracle Data Guard Advantages Compared to Remote Mirroring Solutions. Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover. 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. 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. b. 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. 12) Mention what is split brain syndrome in RAC? Willing to make additional provisions for remote data protection to protect against database, data, and cluster failures and corruptions. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. This architecture is the recommended configuration for Maximum Availability Architecture (MAA). Oracle Enterprise Manager support for patch application simplifies software maintenance. 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. 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. Several standby databases in an Oracle RAC environment residing in a cluster of servers, called a grid server. When the two data centers are located relatively close to each other, extended clusters can provide great protection for some disasters, but not all. 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: Whats new in Oracle Database 12.1.0.2c? Oracle RAC One Node allows you to run one instance of an Oracle RAC database on a single node in a cluster. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. 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)). Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. 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 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. Suppose there are 3 nodes in the following situation. 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. However, if a remote mirroring solution is used for data protection, typically you must mirror the database files, the online redo log, the archived redo logs, and the control file. To ensure data consistency, each instance of a RAC database needs to keep heartbeat with the other instances. 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. Use a physical standby database if read-only access is sufficient. Footnote8With automatic block repair, this should be the most common block corruption repair. 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. Unlike a traditional monolithic database server that is expensive and is not flexible to changing capacity and resource demands, Oracle RAC combines the processing power of multiple interconnected computers to provide system redundancy, scalability, and high availability. Rolling upgrade for system, clusterware, operating system, database, and application. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). These figures show how you can use the Oracle Clusterware framework to make both Oracle Database and your custom applications highly available. 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. Oblivious of the existence of other cluster fragments, each sub-cluster continues to operate independently of the others. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. Oracle Security Features prevent unauthorized access and changes. Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. Oracle Database with Oracle RAC on Extended Clusters. In a typical example, the maximum distance between the systems connected in a point-to-point fashion and running synchronously can be only 10 kilometers. 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. Support for bidirectional replication and updating anything and anywhere. As a result, equal number of database services execute on both the nodes. In a non-RAC Oracle database, a single instance accesses a single database. Automatic block repair may be possible, thus eliminating any downtime in an Oracle Data Guard configuration. 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. Nodes 1,2 can talk to each other. Clients on the network experience a period of lockout while the failover occurs and are then served by the other database instance after the instance has started. This architecture is referred to as an extended cluster. But 1 and 2 cannot talk to 3, and vice versa. These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. You can configure Oracle GoldenGate with Oracle Data Guard to provide protection for the individual databases in the configuration. Traditionally, Oracle RAC is used in a multinode architecture, with many separate database instances running on separate servers. Network addresses are failed over to the backup node. 2. Oracle Database High Availability Architectures, Choosing the Correct High Availability Architecture, Integrating Application Server High Availability, Integrating High Availability for All Applications. 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. 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. 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. Fast Recovery Area manages local recover-related files automatically. 3. 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. 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. 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. Footnote3Recovery time consists largely of the time it takes to restore the failed system. Why is it like that? Simulate loss of connectivity between two nodes. Nodes 1,2 can talk to each other. The script content on this page is for navigation purposes only and does not alter the content in any way. Off-load read-only, reporting, testing and backup activities to the standby database. Thus, this feature allows you to consolidate many databases into a single cluster for easier management, while still providing high availability by quickly relocating instances in the event of server failure. 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. 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. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. The center frame shows the configuration during fast-start failover. Oracle GoldenGate is optimized for replicating data. 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. Table 7-3 Additional Capabilities of High Level Oracle High Availability Architectures, The foundation for all high availability architectures. Split Brain Syndrome in RAC. Oracle Grid Infrastructure and Oracle RAC make use of Redundant Interconnect Usage that distributes network traffic and ensures optimal communication in the cluster. the. Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. An architecture that combines Oracle Database with Oracle RAC is inherently a highly available system. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. This would lead to collision and corruption of shared data as each sub-cluster assumes ownership of shared data. Oracle Data Guard transmits redo data from the primary database to the secondary site to keep the databases synchronized. 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. 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. 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 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. The public and private interconnects, and the Storage Area Network (SAN) are all on separate dedicated channels, with each one configured redundantly. For example, an Oracle Data Guard hub could include multiple databases and applications that are supported in a grid server and storage architecture. Applications scale in an Oracle RAC environment to meet increasing data processing demands without changing the application code. 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. For more information about constructing multiple-source replication environments, see the Oracle GoldenGate documentation. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. Their strategy further mitigates risk by maintaining multiple standby databases, each implemented using a different architecturesRedo Apply and SQL Apply. 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. 1. 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 . Controlfile is used similarly to voting disk in clusterware layer to determine which instance(s) survive and which instance(s) evict. 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 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. 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 . Network connection changes and other site-specific failover activities may lengthen overall recovery time. Then this process is referred as Split Brain Syndrome. For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. 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. 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. 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". All Oracle RAC nodes can be active by implementing multiple Oracle RAC One Node configurations for different databases. Online Reorganization and Redefinition allows for dynamic data changes. A single standby database architecture consists of the following key traits and recommendations: Standby database resides in Site B. At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. 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. 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. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. Common messages in instance alert log are similar to: In above example, instance 2 LMD0 (pid 29940) is the receiver in IPC Send timeout. Hello Friends,Welcome you back on exciting topic, today's session is onNode Membership || Voting Disk || Split Brain Syndrome in Oracle RAC - Real Applicatio. Fast Recovery Area manages local recovery-related files. Dynamic Resource Provisioning allows for dynamic system changes. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. (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. RPO is zero for cluster failover, choice of RPO equal to zero for database failover (Data Guard SYNC), or near-zero (Data Guard ASYNC). 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. An Oracle RAC database is connected to three instances on different nodes. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. Maximum RTO for data corruption, cluster, database, or site failures is in seconds to minutes. Split Brain Syndrome: In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. 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). For example, you can put the files on different disks, volumes, file systems, and so on. Oracle Clusterware provides a number of benefits over third-party clusterware. Oracle Enterprise Management support for Oracle ASM and Oracle ACFS, Grid Plug and Play, Cluster Resource Management, Oracle Clusterware and Oracle RAC Provisioning and patching, Figure 7-4 shows Oracle Database with Oracle RAC architecture. Footnote2The portion of any application connected to the failed system is temporarily affected. Commonly, one will see messages similar to the followings in ocssd.log when split brain happens: Above messages indicate the communication from node 2 to node 1 is not working, hence node 2 only sees 1 node, but node 1 is working fine and it can see two nodes in the cluster. During the process of resolving conflicts, information may be lost or become corrupted. 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. 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. Footnote4Tables can be reorganized online using the DBMS_REDEFINITION package. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. Uses a private network and voting disk-based communication to detect and resolve split-brain Foot 2 scenarios. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. 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.

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