When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. Split Brain Syndrome Basic Concept in Oracle RAC. It also allows the storage to be laid out in a different fashion from the primary computer. The rightmost frame shows the configuration after fast-start failover has occurred. Split Brain Syndrome in RAC. 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 example, you can use your favorite application query in the database check action. Oracle Data Guard is designed to allow businesses get something useful out of their expensive investment in a disaster-recovery site. RAC Split Brain Syndrome. You should adopt the MAA best practices to achieve the optimal recovery time and configuration. You can allocate server resources to multiple instances using Oracle Database Resource Manager Instance Caging. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. It is based on proven Oracle high availability technologies and recommendations. Fully supports Oracle Data Guard. Whatever the case, these Oracle RAC interview questions and answers are for you. Simulate loss of connectivity between two nodes. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). The advantages to using Oracle RAC on extended clusters include: Ability to fully use all system resources without jeopardizing the overall failover times for instance and node failures, Extremely rapid recovery if one site fails, All of the Oracle RAC benefits listed in Section 7.1.4. The second standby database automatically receives data from the new primary database, insuring that data is protected at all times. We will verify that when an equal number of database services are running on both nodes, the node with lower node number (host01) survives. However, when you use Oracle Clusterware, there is no need or advantage to using third-party clusterware. Now talking about split-brain concept with respect to oracle RAC systems, it occurs when the instance These devices convert ESCON or Fibre Channel to the appropriate IP, ATM, or SONET networks. When the two data centers are located relatively close to each other, extended clusters can provide great protection for some disasters, but not all. 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. 2. 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. 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. The group(cohort) with more cluster nodes survive These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. Their strategy further mitigates risk by maintaining multiple standby databases, each implemented using a different architecturesRedo Apply and SQL Apply. Oracle RAC Operational Best Practices for the Cloud Created Date: 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. Fast Recovery Area manages local recovery-related files. If your business does not require the scalability and additional high availability benefits provided by Oracle RAC, but you still need all the benefits of Oracle Data Guard and cold cluster failover, then Oracle Database with Oracle Clusterware and Oracle Data Guard is a good compromise architecture. Furthermore, operational practices across role transitions are simplified when the sites are symmetric. 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. High Availability Architectures and Solutions - Oracle Off-load read-only, reporting, testing and backup activities to the standby database. The script content on this page is for navigation purposes only and does not alter the content in any way. The Oracle Application Server High Availability Guide describes the following high availability services in Oracle Application Server in detail: Process death detection and automatic restart. Footnote1Applications (or a portion of an application) connected to the system that is being maintained may be temporarily affected. For example, you can put the files on different disks, volumes, file systems, and so on. 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. 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 . which node first joined the cluster). 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 . Split brain syndrome in RAC - Oracle Forums Clients are connected to the logical standby database and can work with its data. All Oracle RAC nodes can be active by implementing multiple Oracle RAC One Node configurations for different databases. Suppose there are 3 nodes in the following situation. Oracle recommends that you create and store the local backups in the fast recovery area. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. Network & Disk Heartbeats | Oracle Database Internal Mechanism 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 . Figure 7-1 shows a basic, single-node Oracle Database that includes an Oracle ASM instance.Foot1 This architecture incorporates several high availability features, including Flashback Database, Online Redefinition, Recovery Manager, and Oracle Secure Backup. Logical or user failures that manipulate logical data (DMLs and DDLs). Top 20 Oracle RAC Interview Questions and Answers (2023) - Guru99 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 . This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). Maximum RTO for instance or node failure is in seconds. With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. If the primary system should fail, the first standby database becomes the new primary database. What is split brain in Oracle RAC? - pehdk.afphila.com FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. In the figure, Node 2 is now the active instance connected to the Oracle database and servicing applications and users. host02 is retained as it has higher number of database services executing. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. 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. Oracle GoldenGate is optimized for replicating data. Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. For virtualization, Oracle RAC One Node with Oracle VM increases the benefit of Oracle VM with the high availability and scalability of Oracle RAC. Evaluate logical standby databases if additional indexes are required for reporting purposes and if your application only uses data types supported by logical standby database and SQL Apply. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. 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. 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. Maximum RTO for instance or node failure is in minutes. It allows you to select the table columns depending on a set of criteria. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. You can have up to 32 voting disks in your cluster. Oracle Grid Infrastructure and Oracle RAC make use of Redundant Interconnect Usage that distributes network traffic and ensures optimal communication in the cluster. Support for heterogeneous platforms, versions, and character sets. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. 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 . Support is for single-instance databases only. Then this process is referred as Split Brain Syndrome. 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 RAC Split Brain Syndrome Scenerio - Oracle Forums Several standby databases in an Oracle RAC environment residing in a cluster of servers, called a grid server. Oracle RAC : understanding split brain - The Geek Diary Network addresses are failed over to the backup node. 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. Use a physical standby database if read-only access is sufficient. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. By using specialized devices, this distance can be extended to 66 kilometers. Fine control of information and data sharing are required. 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. For example, if a stray write occurs to a disk, or there is a corruption in the file system, or the host bus adaptor corrupts a block as it is written to disk, then a remote mirroring solution may propagate this corruption to the disaster-recovery site. 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. Then there are two cohorts: {1, 2} and {3}. A world-recognized e-commerce site uses multiple standby databasesa mix of both physical and logical databasesboth for disaster recovery and to scale out read performance by provisioning multiple logical standby databases using SQL Apply. (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.). Database scalability beyond one instance or node. Limited support for mixed platforms. See Section 7.2 for a comparison of the different architectures and highlights of the benefits and considerations. A highly available and resilient application requires that every component of the application must tolerate failures and changes. 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). 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. 3. Oracle RAC Interview Questions | orasolution Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. See Oracle Data Guard Broker for a detailed description of the observer. Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. 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. If the fast recovery area is on the source volume that is remotely mirrored, then you must also remotely mirror the flashback logs. Oracle Database with Oracle RAC architecture provides the following benefits over a traditional monolithic database server and the cold cluster failover model: Flexibility to increase processing capacity using commodity hardware without downtime or changes to the application, Ability to tolerate and quickly recover from computer and instance failures (measured in seconds), Optimized communication in the cluster over redundant network interfaces, without using bonding or other technologies. 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. Start both the services for database admindb so that equal number of database services execute on both the nodes. The data is derived from actual user experiences and from Oracle service requests. With Oracle RAC integration, database scalability is possible. Support for bidirectional replication and updating anything and anywhere. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. All of the business benefits of Oracle RAC and Oracle Data Guard. Then this process is referred as Split Brain Syndrome. Oracle RAC exploits the redundancy that is provided by clustering to deliver availability with n - 1 node failures in an n-node cluster. Customer can designate which server(s) and resource(s) are critical 2. A global manufacturing company used Oracle Data Guard to replace storage-based remote mirroring and maintain a standby database at its recovery site 50 miles away from the primary site. In Oracle RAC, all the instances/servers communicate with each other using a private network. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. 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. Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA. the number of database services executing on a node. Similar to using Oracle Data Guard in SQL Apply mode, Oracle GoldenGate can capture database changes, propagate them to destinations, and apply the changes at these destinations. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. Ina cluster, a private interconnect is used by cluster nodes to monitor each nodes status and communicate with each other. 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. The split brain syndrome and its affects and how it has been managed in oracle is mentioned below. 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. 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 application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. You can define multiple application VIPs, with generally one application VIP defined for each application running. 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. The servers on which you want to run Oracle Clusterware must be running the same operating system. There are numerous high availability features that you can use in the Oracle Database single-instance database architecture. The logical standby database may contain additional indexes and materialized views. But 1 and 2 cannot talk to 3, and vice versa. Oracle Secure Backup provides a centralized tape backup management solution. 1. 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. The fast-start failover has completed and the target standby database is running in the primary database role. As the result, 1 or more instance(s) will be evicted. 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 production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. Nodes 1,2 can talk to each other. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Oracle Database High Availability Architectures, Choosing the Correct High Availability Architecture, Integrating Application Server High Availability, Integrating High Availability for All Applications. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. Name of the cluster: Cluster01.example.com, Number of nodes: 3 (host01, host02, host03), Instances of RAC database: admindb1 on host01. 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. Better performanceOracle Data Guard only transmits write I/Os to the redo log files of the primary database, whereas remote mirroring solutions must transmit these writes and every write I/O to data files, additional members of online log file groups, archived redo log files, and control files. Oracle RAC builds higher levels of availability on top of the standard Oracle Database features. Why is it like that? What is Voting Disk & Split Brain Syndrome in RAC
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