Oracle Database High Availability Architectures, Choosing the Correct High Availability Architecture, Integrating Application Server High Availability, Integrating High Availability for All Applications. Suppose there are 3 nodes in the following situation. The voting result is similar to clusterware voting result. Oracle RAC exploits the redundancy that is provided by clustering to deliver availability with n - 1 node failures in an n-node cluster. Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. 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 . This architecture is referred to as an extended cluster. 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. Footnote3For qualified one-off patches only. 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. 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. Maximum RTO for instance or node failure is in minutes. This architecture is the recommended configuration for Maximum Availability Architecture (MAA). Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. The goal of the MAA is to remove the complexity in designing the optimal high availability architecture by providing configuration recommendations and tuning tips to optimize your architecture and Oracle features. When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. Note, however, that the synchronous redo transport does not impose any physical distance limitation. To maintain the standby site for failover, not only must the standby site contain homogeneous installations and applications, data and configurations must also be synchronized constantly from the production site to the standby site. 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. split brain syndrome. 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. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. Oracle GoldenGate is optimized for replicating data. These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. There are three typical causes of corruption: 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. . The operation of an Oracle Clusterware cold cluster failover is depicted in Figure 7-2 and Figure 7-3. RAC Split Brain Syndrome. Use a physical standby database if read-only access is sufficient. Then there are two cohorts: {1, 2} and {3}. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. For more information, see the "Administering Oracle RAC One Node" section in the Oracle Real Application Clusters Administration and Deployment Guide. 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. 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. Then this process is referred as Split Brain Syndrome. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. For more information see the MAA white paper "Rapid Oracle RAC One Node Standby Deployment" at. Better resilience and data protectionOracle Data Guard ensures much better data protection and data resilience than remote mirroring solutions. A single standby database architecture consists of the following key traits and recommendations: Standby database resides in Site B. Oracle Application Server instances can be installed in either site as long as they do not interfere with the instances in the disaster recovery setup. 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. 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. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. Footnote2Rolling upgrades with Oracle Data Guard incur minimal downtime. In order to make largest number of resources available to the users, the node weight is computed for each node based on number of the resource executing on it and the sub-cluster with higher weight will survive. In previous releases, technologies like bonding or trunking were used to make use of redundant networks for the interconnect. If you configure a single voting disk, then you should use external mirroring to provide redundancy. High availability benefits and workload balancing outweigh performance concerns. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. Simulate loss of connectivity between two nodes. 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 . Database scalability beyond one instance or node. 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. What is split brain in Oracle RAC? Online Patching allows for dynamic database patching of typical diagnostic patches. The fast-start failover has completed and the target standby database is running in the primary database role. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. From the entry point to an Oracle Application Server system (content cache) to the back-end layer (data sources), all the tiers that are crossed by a request can be configured in a redundant manner with Oracle Application Server. 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 servers on which you want to run Oracle Clusterware must be running the same operating system. 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. Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. 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. 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. 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 Database is a single-instance, standalone (noncluster) database and it is the foundation for all high availability architectures. Now talking about split-brain concept with respect to oracle . Footnote7Recovery time depends on block media recovery and the time it takes to restore a consistent block from the flashback logs or database backups, and to recover the block by applying all the redo from archive logs and online redo logs. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. 2. End-users connect to clusters through a public network. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. 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. Oracle Data Guard transmits redo data from the primary database to the secondary site to keep the databases synchronized. The recommended high availability and disaster-recovery architectures that use Oracle Data Guard are described in the following sections: Overview of Single Standby Database Architectures, Overview of Multiple Standby Database Architectures. We will verify that when an equal number of database services are running on both nodes, the node with lower node number (host01) survives. 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. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). 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. In such a scenario, integrity of the cluster and its data might be compromised due to uncoordinated writes to shared data by independently operating nodes. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle One Node database. Higher ROIBusinesses must obtain maximum value from their IT investments, and ensure that no IT infrastructure is sitting idle. 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. This book focuses primarily on the database high availability solutions. Online Reorganization and Redefinition allows for dynamic data changes. 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. You can define multiple application VIPs, with generally one application VIP defined for each application running. With Database Server Grid and Database Storage Grid (described in Section 5.2 and Section 5.3), you can build standby database and testing hubs that use a pool of system resources. Since I will only explore the scenarios for which functionality has been modified, i.e. It allows you to select the table columns depending on a set of criteria. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. Fast-Start Fault Recovery bounds and optimizes instance and database recovery times to minutes. Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. If it takes seconds to detect a malicious DML or DLL transaction, it typically only requires seconds to flash back the appropriate transactions. Fast Recovery Area manages local recovery-related files. You should determine if both sites are likely to be affected by the same disaster. Building on top of the local high availability solutions is the Oracle Application Server disaster recovery solution. host01 is retained as it has a lower node number. Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. For more information about constructing multiple-source replication environments, see the Oracle GoldenGate documentation. You can configure Oracle GoldenGate with Oracle Data Guard to provide protection for the individual databases in the configuration. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. 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 can capture data changes at the primary database or downstream at a replica database, thus enabling users to build hub-and-spoke network configurations that can support hundreds of replica databases. For storage migration, you are required to use both storage arrays by Oracle ASM temporarily. 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. Oracle RAC One Node provides relocation of Oracle RAC primary and standby databases configured with Oracle Data Guard (This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2)). Oracle Data Guard Advantages Over Traditional Solutions. 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. Limited support for mixed platforms. 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 ). 1. Whatever the case, these Oracle RAC interview questions and answers are for you. Vijay.Cherukuri-Oracle Dec 18 2011 edited Nov 5 2012. However, when the data centers are located more than 66 kilometers apart, you must use a series of repeaters and converters from third-party vendors. Uses a private network and voting disk-based communication to detect and resolve split-brain Foot 2 scenarios. But 1 and 2 cannot talk to 3, and vice versa. 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. Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. However, if a remote mirroring solution is used for data protection, typically you must mirror the database files, the online redo log, the archived redo logs, and the control file. 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. 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. By reducing the combinations of software that you must coordinate and support, you can increase the manageability and availability of your system software. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. Also, see Figure 5-2 for another example of a multiple standby database environment. With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. Node Weighting for Split Brain Resolution Without better understanding of what is critical or of higher priority to the customer's workload, Oracle Clusterware has always resolved split brain conditions in favor of the cluster cohort containing the node with the lowest node number (i.e. 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. The Oracle Data Guard broker communicates with the production database, the physical standby database, and the logical standby database. Table 7-2 High Availability Architecture Recommendations. After the former primary database has been repaired, the observer reestablishes its connection to that database and reinstates it as a new standby database. Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. 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. Why is it like that? Table 7-3 Additional Capabilities of High Level Oracle High Availability Architectures, The foundation for all high availability architectures. Automatic block repair may be possible, thus eliminating any downtime in an Oracle Data Guard configuration. The high availability benefits to using Oracle RAC One Node include the following: Offers better database availability than traditional cold failover solutions, Provides better virtualization for databases than hypervisor-based solutions, Enables online migration of database instances and online patching and upgrading of operating system and database software (incurring no downtime), Delivers a comprehensive, single-vendor solution, with no need to implement third-party products, Is ready to scale and upgrade to multinode Oracle RAC, Provides a standardized environment and a common toolset for both single-node and multinode Oracle database deployments, Is less expensive than cold fail over solutions or a full Oracle RAC deployment. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. 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. Logical or user failures that manipulate logical data (DMLs and DDLs). Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Then there are two cohorts: {1, 2} and {3}. Oracle RAC builds higher levels of availability on top of the standard Oracle Database features. 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. Q39) Mention what is split brain syndrome in RAC? 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. Rolling upgrade for system, clusterware, operating system, database, and application. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. They will enhance your knowledge and help you to emerge as the best candidate. 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. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). Maximum RTO for data corruption, cluster, database, or site failures is in seconds to minutes. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. Unlike the cold cluster model where one node is completely idle, all instances and nodes can be active to scale your application. 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. 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. 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. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. Support for heterogeneous platforms, versions, and character sets. Dynamic Resource Provisioning allows for dynamic system changes. 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. Network addresses are failed over to the backup node. the number of database services executing on a node. 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. The script content on this page is for navigation purposes only and does not alter the content in any way. Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). (For complete disaster recovery and data protection, use the architecture shown in Figure 7-8.). This chapter describes the various high availability architectures in an Oracle environment and helps you to choose the correct architecture for your organization.
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