Recovery Manager optimizes local repair of data failures using local backups. 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. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. 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. You can configure the failed application connections to fail over to the replica. Higher ROIBusinesses must obtain maximum value from their IT investments, and ensure that no IT infrastructure is sitting idle. Fast Recovery Area manages local recovery-related files. 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. By using specialized devices, this distance can be extended to 66 kilometers. For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. 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. Support is for single-instance databases only. Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. End-users connect to clusters through a public network. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. It allows you to select the table columns depending on a set of criteria. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. If it takes seconds to detect a malicious DML or DLL transaction, it typically only requires seconds to flash back the appropriate transactions. They will enhance your knowledge and help you to emerge as the best candidate. 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. Maximum RTO for instance or node failure is in seconds to minutes. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. All of the business benefits of Oracle RAC and Oracle Data Guard. Automatic block repair may be possible, thus eliminating any downtime in an Oracle Data Guard configuration. (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. 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 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. 12) Mention what is split brain syndrome in RAC? Oracle Clusterware provides a number of benefits over third-party clusterware. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. which node first joined the cluster). 1. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. Provides the simplicity of a physical replica. Then there are two cohorts: {1, 2} and {3}. When a database is started, Oracle Database allocates a memory area called the System Global Area (SGA) and starts one or more Oracle Database processes. Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. During the process of resolving conflicts, information may be lost or become corrupted. 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 . Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. Maximum RTO for instance or node failure is in minutes. 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. Split Brain Resolution in Oracle Clusterware 12c Rel 2 1. Hi Guru's. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). An Oracle RAC database is connected to three instances on different nodes. Oracle Automatic Storage Management (Oracle ASM) and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and usage. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. So, in a two node situation both the instances will think that the other instance is down because of lack of connection. At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. Rolling upgrade for system, clusterware, operating system, database, and application. Provides maximum protection from physical corruptions. For more information see the MAA white paper "Rapid Oracle RAC One Node Standby Deployment" at. Oracle recommends that you use automatic undo management with sufficient space to attain your desired undo retention guarantee, enable Oracle Flashback Database, and allocate sufficient space and I/O bandwidth in the fast recovery area. Limited support for mixed platforms. 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. For example, Table 7-1 provides some insight into the probability of different outages during unplanned and planned activities. It also gives users complete control over the routing of change records from the primary database to a replica 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. This book focuses primarily on the database high availability solutions. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. These updates are discarded when the snapshot database is reconverted to a physical standby database. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. Oracle Database High Availability Best Practices for information about configuring Oracle Database 11g with Oracle RAC on extended clusters, White papers about extended (stretch) clusters and about using standard NFS to support a third voting disk on an extended cluster configuration at http://www.oracle.com/technetwork/database/clustering/overview/. 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 . You should determine if both sites are likely to be affected by the same disaster. Recovery Manager (RMAN) optimizes local repair of data failures. Oracle Data Guard is operating in a steady state, with the primary database transmitting redo data to the target standby database and the observer monitoring the state of the entire configuration. You can allocate server resources to multiple instances using Oracle Database Resource Manager Instance Caging. 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. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. The script content on this page is for navigation purposes only and does not alter the content in any way. RAC Split Brain Syndrome. 1. 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. With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. This configuration consists of a central resource supporting 10 applications and databases in the grid, rather than managing 10 separate system or storage units in a nongrid infrastructure. 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. Uses a private network and voting disk-based communication to detect and resolve split-brain Foot 2 scenarios. Name of the cluster: Cluster01.example.com, Number of nodes: 3 (host01, host02, host03), Instances of RAC database: admindb1 on host01. Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. Traditionally, Oracle RAC is used in a multinode architecture, with many separate database instances running on separate servers. Although both types of solutions provide high availability, active-active solutions generally offer higher scalability and faster failover, although they tend to be more expensive. The rightmost frame shows the configuration after fast-start failover has occurred. 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. Oracle Application Server provides redundancy by offering support for multiple instances supporting the same workload. Footnote4Tables can be reorganized online using the DBMS_REDEFINITION package. 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 Data Guard is designed to allow businesses get something useful out of their expensive investment in a disaster-recovery site. See Section 7.2 for a comparison of the different architectures and highlights of the benefits and considerations. 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. 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 . The public and private interconnects, and the Storage Area Network (SAN) are all on separate dedicated channels, with each one configured redundantly. Oracle RAC Operational Best Practices for the Cloud Created Date: 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. 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. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. Consider using Oracle Database with Oracle GoldenGate if one or more of the following conditions are true: Updates are required on both sites or databases, and the changes must be propagated bidirectionally. Voting disk is used by Oracle Cluster Synchronization Services Daemon (ocssd) on each node, to mark its own attendance and also to record the nodes it can communicate with. By reducing the combinations of software that you must coordinate and support, you can increase the manageability and availability of your system software. The group(cohort) with more cluster nodes survive Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. Footnote1Applications (or a portion of an application) connected to the system that is being maintained may be temporarily affected. 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). Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. It also allows the storage to be laid out in a different fashion from the primary computer. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle One Node database. For example : 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. Use a physical standby database if read-only access is sufficient. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. Footnote1Recovery time indicated applies to database and existing connection failover. See Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)" for more information about the best practices documentation. Split brain scenario - RAC and PXC. 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. Online Reorganization and Redefinition allows for dynamic data changes. There is no fancy or expensive hardware required. The center frame shows the configuration during fast-start failover. An exception is undropping a table, which is literally instantaneous regardless of detection time. 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. Also, for large data centers with a need to support many applications with Oracle Data Guard requirements, you can build an Oracle Data Guard hub to reduce the total cost of ownership. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. 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. Clusterware will evaluate cluster resources on implied workload 3. . Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). 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. Even though split brain scenario occurs in both Oracle RAC and Percona's XtraDB Cluster, a two node cluster is allowed and split brain scenario is resolved in RAC but a two node is not recommended in Percona Cluster ( 3 nodes is recommended ). 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. Table 7-2 High Availability Architecture Recommendations. In a non-RAC Oracle database, a single instance accesses a single database. Footnote2Oracle ASM automatically rebalances stored data when disks are added or removed while the database remains online. Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. Support for fine-grained, n-way multimaster, hub-and-spoke, or many-to-one replication architectures. In a split brain situation, voting disk will be used to determine which node(s) survive and which node(s) will be evicted. 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. 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. The logical standby database may contain additional indexes and materialized views. 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. 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 . Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. A highly available application must analyze every component that affects the application, including the network topology, application server, application flow and design, systems, and the database configuration and architecture. 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. All of the business benefits of Oracle RAC. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. If the sub-clusters are of the different sizes, the functionality is same as earlier i.e. 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. 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. Additional protection from data center failure with special considerations that are documented in Section 7.1.4.1, Highest level of availability for server or computer room failure. Oracle Clusterware manages the availability of both the user applications and Oracle databases. The problem which could arise out of this situation is that the sane . For high availability, Oracle recommends that you have a minimum of three voting disks. Typically, this is not possible with remote mirroring solutions. The fast-start failover has completed and the target standby database is running in the primary database role. 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. End-users connect to clusters through a public network. Then this process is referred as Split Brain Syndrome. 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.
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