what is split brain in oracle rac

Ina cluster, a private interconnect is used by cluster nodes to monitor each nodes status and communicate with each other. See Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)" for more information about the best practices documentation. 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. Uses a private network and voting disk-based communication to detect and resolve split-brain Foot 2 scenarios. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. Provides seamless integration with, and migration to, Oracle Real Application Clusters (Oracle RAC) and Oracle Data Guard. Figure 7-7 shows the production database at the primary site and multiple standby databases at secondary sites. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. Top 25 Oracle RAC Interview Questions and Answers in 2023 There are three typical causes of corruption: 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. Different character sets are required between the primary database and its replicas. 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. 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. Footnote1Rolling upgrades with Oracle Clusterware and Oracle RAC incur zero downtime. In Oracle RAC, all the instances/servers communicate with each other using a private network. Footnote1Architectures for which the MO is high might require additional time and expertise to build and maintain, but offer increased flexibility and capabilities required to meet specific business requirements. The following list summarizes the advantages of using Oracle Data Guard compared to using remote mirroring solutions: Better network efficiencyWith Oracle Data Guard, only the redo data needs to be sent to the remote site and the redo data can be compressed to provide even greater network efficiency. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. Table 7-4 shows the recovery time (including detection and client failover time) of an integrated Oracle client, whenever relevant. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. Split brain scenario - RAC and PXC. 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 in RAC Database | RAC DBA Training - YouTube Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. The center frame shows the configuration during fast-start failover. Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. the number of database services executing on a node. 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. Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. Footnote3Recovery time consists largely of the time it takes to restore the failed system. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. 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. The logical standby database may contain additional indexes and materialized views. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. As the result, 1 or more instance(s) will be evicted. This chapter describes the various high availability architectures in an Oracle environment and helps you to choose the correct architecture for your organization. Oracle RAC Split Brain Syndrome Scenerio. sub-clusters are of equal size, I have shut down one of the nodes so that there are only 2 active nodes in the cluster. 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. Nodes 1,2 can talk to each other. An infrastructure services provider to the telecommunication industry uses a single standby database located over 400 miles away from the primary database configured for synchronous redo transport, enabling zero-data-loss failover for maximum data protection and high availability. Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. Oracle RAC - Wikipedia 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. Oblivious of the existence of other cluster fragments, each sub-cluster continues to operate independently of the others. Suppose there are 3 nodes in the following situation. The premise of the Data Guard hub is that it provides higher utilization with lower cost. Note, however, that the synchronous redo transport does not impose any physical distance limitation. See Oracle Data Guard Broker for a detailed description of the observer. Oracle Data Guard provides a number of advantages over traditional solutions, including the following: Fast, automatic or automated database failover for data corruptions, lost writes, and database and site failures, Automatic corruption repair automatically replaces a corrupted block on the primary or physical standby by copying a good block from a physical standby or primary database, Most comprehensive protection against data corruptions and lost writes on the primary database, Reduced downtime for storage, Oracle ASM, Oracle RAC, system migrations and some platform migrations, and changes using Data Guard switchover, Reduced downtime with Oracle Data Guard rolling upgrade capabilities, Ability to off-load primary database activitiessuch as backups, queries, or reportingwithout sacrificing the RTO and RPO ability to use the standby database as a read-only resource using the real-time query apply lag capability, Ability to integrate non-database files using Oracle Database File System (DBFS) as part of the full site failover operations, No need for instance restart, storage remastering, or application reconnections after site failures, Transparent and integrated support for application failover. Fine control of information and data sharing are required. 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. 2. mysql - Split brain scenario - RAC and PXC - Database Administrators Customer can designate which server(s) and resource(s) are critical 2. To simulate loss of connectivity between two nodes, stop the private network service on one of the nodes: Verify that host01 is retained as it has a lower node number and host02 is evicted: To simulate loss of connectivity between two nodes, stop private network service on one of the nodes: Verify that host02 is retained as it has higher number of database services executing and host01 is evicted although it has a lower node number: If the sub-clusters are of the different sizes, the functionality is same as earlier, i.e. Oracle Clusterware: Enables you to use an entire software solution from Oracle, avoiding the cost and complexity of maintaining additional cluster software. SELECT statements might be as straightforward as selecting a few . The figure shows Oracle Database with Oracle Data Guard architecture. 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. Footnote6Recovery time for human errors depend primarily on detection time. Footnote3The initial investment to build a robust solution is well worth the long-term flexibility and capabilities that Oracle GoldenGate delivers to meet specific business requirements. After the former primary database has been repaired, the observer reestablishes its connection to that database and reinstates it as a new standby database. If you configure a single voting disk, then you should use external mirroring to provide redundancy. split brain syndrome. Although traditional solutions (such as backup and recovery from tape, storage-based remote mirroring, and database log shipping) can deliver some level of high availability, Oracle Data Guard provides the most comprehensive high availability and disaster recovery solution for Oracle databases. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. 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. Oracle RAC : understanding split brain - The Geek Diary Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. The Oracle Data Guard broker communicates with the production database, the physical standby database, and the logical standby database. Split Brain Syndrome | Oracle Database Internal Mechanism With the snapshot standby database hub, you can use the combined storage and server resources of a grid instead of building and managing individual servers for each application. So, in a two node situation both the instances will think that the other instance is down because of lack of connection. host01 is evicted although it has a lower node number. End-users connect to clusters through a public network. 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. Oracle Secure Backup provides a centralized tape backup management solution. Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). 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. 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. 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. Provides maximum protection from physical corruptions. 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. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. High Availability Architectures and Solutions - Oracle Database scalability beyond one instance or node. This is often called the multi-master problem. Since I will only explore the scenarios for which functionality has been modified, i.e. In a "split brain" situation, voting disk is used to determine which node (s) will survive and which node (s) will be evicted. The public and private interconnects, and the Storage Area Network (SAN) are all on separate dedicated channels, with each one configured redundantly. Footnote1Recovery time indicated applies to database and existing connection failover. The data is derived from actual user experiences and from Oracle service requests. Maximum RTO for instance or node failure is zero for the databaseFootref1. High availability functionality to manage third-party applications, Rolling release upgrades of Oracle Clusterware. which node first joined the cluster). The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. In Oracle Database 11g Release 2 (11.2), Oracle RAC One Node or Oracle RAC is the preferred solution over Oracle Clusterware (Cold Cluster Failover) because it is a more complete and feature-rich solution. Hi Guru's. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). Footnote8With automatic block repair, this should be the most common block corruption repair. Now talking about split-brain concept with respect to oracle . This architecture is the recommended configuration for Maximum Availability Architecture (MAA). Oracle Enterprise Manager support for patch application simplifies software maintenance. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. 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. 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. 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. (For complete disaster recovery and data protection, use the architecture shown in Figure 7-8.). Footnote2Oracle ASM automatically rebalances stored data when disks are added or removed while the database remains online. host01 is retained as it has a lower node number. Dynamic Resource Provisioning allows for dynamic system changes. There is no fancy or expensive hardware required. If zero data loss is required with minimum performance impact on the primary database, then the best practice is to locate the secondary site within 200 miles of the primary database. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. 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. At the time of role transition, more storage and system resources can be allocated toward that application. The figure shows users making local updates to the snapshot standby database. This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. 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 heartbeat is maintained by background processes like LMON, LMD, LMS and LCK. More investment and expertise to build and maintain an integrated high availability solution is available. In a non-RAC Oracle database, a single instance accesses a single database. The instances monitor each other by checking "heartbeats." Oracle Application Server provides redundancy by offering support for multiple instances supporting the same workload. If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. What is split brain in RAC? - TheNewsIndependent Split Brain Syndrome, In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. Then this process is referred as Split Brain Syndrome. In previous releases, technologies like bonding or trunking were used to make use of redundant networks for the interconnect. What is Voting Disk & Split Brain Syndrome in RAC To avoid splitbrain, node 2 aborted itself. 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. 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. 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. Online Reorganization and Redefinition allows for dynamic data changes. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. Willing to make additional provisions for remote data protection to protect against database, data, and cluster failures and corruptions. Oracle Database is a single-instance, standalone (noncluster) database and it is the foundation for all high availability architectures. With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. As a result, equal number of database services execute on both the nodes. However, remote mirroring solutions affect DBWR process performance because they subject all DBWR process write I/O's to network and disk I/O induced delays inherent to synchronous, zero-data-loss configurations. Oracle RAC Interview Questions | orasolution 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. 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. You might choose to use Oracle GoldenGate to configure and maintain a logical copy of your production database. 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. Split Brain Syndrome in RAC. Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. 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. The SELECT statement is used to retrieve information from a database. 12) Mention what is split brain syndrome in RAC? You can define multiple application VIPs, with generally one application VIP defined for each application running. Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. As per Split brain syndrome in Oracle RAC in case of inter-connect failures the master node will evict other/dead nodes . 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. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. Also, you can use the Oracle Clusterware ability to relocate applications and application resources (using the crsctl relocate resource command) as a way to move the workload to another node so that you can perform planned system maintenance on the production server.
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