Footnote3For qualified one-off patches only. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. Footnote4Database is still available, but a portion of the application connected to the failed system is temporarily affected. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. The common voting result will be: a. Clients are connected to the logical standby database and can work with its data. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. Ina cluster, a private interconnect is used by cluster nodes to monitor each nodes status and communicate with each other. Oracle Enterprise Manager support for patch application simplifies software maintenance. Recovery Manager (RMAN) optimizes local repair of data failures. Oracle RAC Split Brain Syndrome Scenerio. Figure 7-7 shows the production database at the primary site and multiple standby databases at secondary sites. 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. 12) Mention what is split brain syndrome in RAC? RAC Split Brain Syndrome. 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, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. Then there are two cohorts: {1, 2} and {3}. For example, Table 7-1 provides some insight into the probability of different outages during unplanned and planned activities. 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. (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. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. 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 high availability, Oracle recommends that you have a minimum of three voting disks. If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. The second standby database automatically receives data from the new primary database, insuring that data is protected at all times. When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. Oracle Clusterware: Enables you to use an entire software solution from Oracle, avoiding the cost and complexity of maintaining additional cluster software. 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. End-users connect to clusters through a public network. When the two data centers are located relatively close to each other, extended clusters can provide great protection for some disasters, but not all. The voting result is similar to clusterware voting result. It is based on proven Oracle high availability technologies and recommendations. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. The split brain syndrome and its affects and how it has been managed in oracle is mentioned below. 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 . 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. The servers on which you want to run Oracle Clusterware must be running the same operating system. You can achieve the highest level of availability when using Oracle RAC and Oracle Data Guard and there is no need to make application changes to use these Oracle Database features. 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. Also, see Figure 5-2 for another example of a multiple standby database environment. 2. An Oracle RAC extended cluster is an architecture that provides extremely fast recovery from a site failure and allows for all nodes, at all sites, to actively process transactions as part of single database cluster. But 1 and 2 cannot talk to 3, and vice versa. If all the sub-clusters are of the same size, the sub-cluster having the lowest numbered node survives so that, in a 2-node cluster, the node with the lowest node number will survive. The following list describes some implementations for a multiple standby database architecture: Continuous and transparent disaster or high availability protection if an outage occurs at the primary database or the targeted standby database, Regional reporting or reader databases for better response time, Synchronous redo transport that transmits to a more local standby database, and asynchronous redo transport that transmits to a more remote standby database for optimum levels of performance and data protection, Transient logical standby databases (described in Section 3.6.3) for minimal downtime rolling upgrades, Test and development clones using snapshot standby databases (described in Section 3.6.4), Scaling the configuration by creating additional logical standby databases or snapshot standby databases. For more information see the MAA white paper "Rapid Oracle RAC One Node Standby Deployment" at. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. You should adopt the MAA best practices to achieve the optimal recovery time and configuration. 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. High availability solution with added data and disaster recovery protection. Oracle Data Guard is designed so that it does not affect the Oracle database writer (DBWR) process that writes to data files, because anything that slows down the DBWR process affects database performance. 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 ). Support for bidirectional replication and updating anything and anywhere. 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. The operation of an Oracle Clusterware cold cluster failover is depicted in Figure 7-2 and Figure 7-3. 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. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. Simulate loss of connectivity between two nodes. 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. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. The clusters that are typical of Oracle RAC environments can provide continuous service for both planned and unplanned outages. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. 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. 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 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. With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. Split Brain Syndrome in RAC. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. 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. 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)). Oracle Clusterware provides a number of benefits over third-party clusterware. 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. Suppose there are 3 nodes in the following situation. 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. 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. This chapter describes the various high availability architectures in an Oracle environment and helps you to choose the correct architecture for your organization. Online Reorganization and Redefinition allows for dynamic data changes. Section 7.1.8 describes how you can achieve the highest level of availability with Oracle RAC and Oracle Data Guard. Fast Recovery Area manages local recover-related files automatically. Oracle Data Guard Advantages Compared to Remote Mirroring Solutions. Then there are two cohorts: {1, 2} and {3}. Oracle recommends that you create and store the local backups in the fast recovery area. In simple terms Split brain means that there are 2 or more distinct sets of nodes, or cohorts, with no communication between the two cohorts. Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. 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. At the time of role transition, more storage and system resources can be allocated toward that application. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. Oracle Application Server provides redundancy by offering support for multiple instances supporting the same workload. 1. Furthermore, the standby databases can be used for read-only access and subsequently for reader farms, for reporting, and for testing and development. 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. But 1 and 2 cannot talk to 3, and vice versa. Fully supports Oracle Data Guard. For more information, see Oracle Data Guard Concepts and Administration or the Oracle Streams Replication Administrator's Guide. Oracle RAC Split Brain Syndrome Scenerio. 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. 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. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. 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. 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. The production database is connected over the network to the physical standby database site and the logical standby database site (the standby databases may be at the same or different sites). The configuration can be an active-active configuration using Oracle Application Server Cluster or an active-passive configuration using Oracle Application Server Cold Cluster Failover. As per Split brain syndrome in Oracle RAC in case of inter-connect failures the master node will evict other/dead nodes . All Oracle RAC nodes can be active by implementing multiple Oracle RAC One Node configurations for different databases. In Oracle RAC, all the instances/servers communicate with each other using a private network. Dynamic Resource Provisioning allows for dynamic system changes. It requires only a standard TCP/IP-based network link between the two computers. It supports bidirectional replication, data transformations, subsetting, custom apply functions, and heterogeneous platforms. This book focuses primarily on the database high availability solutions. 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. The logical standby database may contain additional indexes and materialized views. Footnote2Rolling upgrades with Oracle Data Guard incur minimal downtime. Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. Fast-start failover is recommended to provide automatic failover without user intervention and bounded recovery time. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. 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. Better resilience and data protectionOracle Data Guard ensures much better data protection and data resilience than remote mirroring solutions. 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. Better functionalityOracle Data Guard provides full suite of data protection features that provide a much more comprehensive and effective solution optimized for data protection and disaster recovery than remote mirroring solutions. 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. 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. As a result, equal number of database services execute on both the nodes. The probability of failing over all databases at the same time is unlikely. For physical standby databases, this solution: Supports very high primary database throughput. The script content on this page is for navigation purposes only and does not alter the content in any way. 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. Another possible configuration might be a testing hub consisting of snapshot standby databases. Maximum RTO for instance or node failure is in seconds. The public and private interconnects, and the Storage Area Network (SAN) are all on separate dedicated channels, with each one configured redundantly. See Section 7.1.3, "Oracle Database with Oracle RAC One Node" for more information. What Is Oracle RAC. This is often called the multi-master problem. 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/. Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover). Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. After the former primary database has been repaired, the observer reestablishes its connection to that database and reinstates it as a new standby database. 2. 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. 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. 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. Oracle Security Features prevent unauthorized access and changes. Unlike the cold cluster model where one node is completely idle, all instances and nodes can be active to scale your application. In Oracle RAC, all the instances/servers communicate with each other using a private network. To avoid splitbrain, node 2 aborted itself. The following list describes examples of Oracle Data Guard configurations using multiple standby databases: A world-recognized financial institution uses two remote physical standby databases for continuous data protection after failover. 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. Each site is a self-contained system. 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 . Table 7-3 Additional Capabilities of High Level Oracle High Availability Architectures, The foundation for all high availability architectures. Fast Recovery Area manages local recovery-related files. Note, however, that the synchronous redo transport does not impose any physical distance limitation. Oracle Secure Backup provides a centralized tape backup management solution. 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. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. 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. 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 . Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. Footnote8With automatic block repair, this should be the most common block corruption repair. Use a physical standby database if read-only access is sufficient. 3. Rolling upgrade for system, clusterware, operating system, database, and application. There are numerous high availability features that you can use in the Oracle Database single-instance database architecture. 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 . The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. You can have up to 32 voting disks in your cluster. Database scalability beyond one instance or node. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. You can configure Oracle GoldenGate with Oracle Data Guard to provide protection for the individual databases in the configuration. So, in a two node situation both the instances will think that the other instance is down because of lack of connection. If the node running your Oracle RAC One Node becomes overloaded, you can relocate the instance to another node in the cluster using the online database relocation utility (srvctl relocate database), with no downtime for application users.
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