This chapter describes the various high availability architectures in an Oracle environment and helps you to choose the correct architecture for your organization. Note, however, that the synchronous redo transport does not impose any physical distance limitation. 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. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. All of the business benefits of Oracle RAC. The probability of failing over all databases at the same time is unlikely. 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. (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.). The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. 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. With Oracle RAC integration, database scalability is possible. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). The figure shows users making local updates to the snapshot standby database. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. Limited support for mixed platforms. 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. In Oracle RAC, all the instances/servers communicate with each other using a private network. You can configure the failed application connections to fail over to the replica. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. Each instance is associated with a service: HR, Sales, and Call Center. Then this process is referred as Split Brain Syndrome. Then this process is referred as Split Brain Syndrome. 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. 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)). Their strategy further mitigates risk by maintaining multiple standby databases, each implemented using a different architecturesRedo Apply and SQL Apply. 3. Footnote3For qualified one-off patches only. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. Oracle Application Server provides high availability and disaster recovery solutions for maximum protection against any kind of failure with flexible installation, deployment, and security options. The script content on this page is for navigation purposes only and does not alter the content in any way. The group(cohort) with more cluster nodes survive 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. . Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. Split brain scenario - RAC and PXC. We will verify that when an equal number of database services are running on both nodes, the node with lower node number (host01) survives. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. Furthermore, operational practices across role transitions are simplified when the sites are symmetric. We will verify that when an unequal number of database services are running on the two nodes, the node hosting the higher number of database services survives even if it has a higher node number. Starting from 12.1.0.2, during split brain resolution, the new algorithm followed to decide the nodes to be evicted/retained is as follows: Fortnightly newsletters help sharpen your skills and keep you ahead, with articles, ebooks and opinion to keep you informed. Footnote8With automatic block repair, this should be the most common block corruption repair. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. 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 data is derived from actual user experiences and from Oracle service requests. 817202 Mar 1 2016 edited Mar 2 2016. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. 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. 1. Oracle GoldenGate is optimized for replicating data. 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. It also allows the storage to be laid out in a different fashion from the primary computer. Rolling upgrade for system, clusterware, operating system, database, and application. Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover. Oracle RAC Split Brain Syndrome Scenerio. For more information about constructing multiple-source replication environments, see the Oracle GoldenGate documentation. 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. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. The heartbeat is maintained by background processes like LMON, LMD, LMS and LCK. High availability benefits and workload balancing outweigh performance concerns. This is often called the multi-master problem. To protect against site failures, the MAA recommends that Oracle RAC and Oracle Data Guard reside on separate systems (clusters) and data centers. Now talking about split-brain concept with respect to oracle . You can have up to 32 voting disks in your cluster. In Oracle RAC each node in the cluster is interconnected through a private interconnect. 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. Online Patching allows for dynamic database patches for diagnostic and interim patches. Automatic block repair may be possible, thus eliminating any downtime in an Oracle Data Guard configuration. Use a physical standby database if read-only access is sufficient. Upon detecting the break in communication, the observer attempts to reestablish a connection with the primary database for the amount of time defined by the FastStartFailoverThreshold property before initiating a fast-start failover. See Section 7.1.3, "Oracle Database with Oracle RAC One Node" for more information. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. Then there are two cohorts: {1, 2} and {3}. For example, you can put the files on different disks, volumes, file systems, and so on. There are numerous high availability features that you can use in the Oracle Database single-instance database architecture. host02 is retained as it has higher number of database services executing. Oracle GoldenGate can capture changes at a source database, and the captured changes can be propagated asynchronously to replica databases. During the process of resolving conflicts, information may be lost or become corrupted. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. Oracle Automatic Storage Management and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and utilization. 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. 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. The individual nodes are running fine and can accept user connections and work . pagespeed.lazyLoadImages.overrideAttributeFunctions(); Oracle Flashback Technology optimizes logical failure repair. Recovery Manager (RMAN) optimizes local repair of data failures. Whatever the case, these Oracle RAC interview questions and answers are for you. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. The group(cohort) with lower node member survive, in case of same number of node(s) available in each group. The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. When you move the Oracle RAC One Node instance to the newly resized Oracle VM node, you can dynamically increase any limits programmed with Resource Manager Instance Caging. 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. Table 7-2 High Availability Architecture Recommendations. Check that only two nodes (host01 and host02) are active and host01 has lower node number: Create two singleton services for the RAC database admindb: Verify that admindb is the only database in the cluster having its instances executing on host01 and host02. The voting result is similar to clusterware voting result. 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. 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. Fast Recovery Area manages local recover-related files automatically. 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. In a split brain situation, voting disk will be used to determine which node(s) survive and which node(s) will be evicted. 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. Customer can designate which server(s) and resource(s) are critical 2. 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. New requests are accepted after the Split-Brain event and then performed on potentially corrupted system state (thus potentially corrupting system state even further). Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. Oracle Clusterware provides a number of benefits over third-party clusterware. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. 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. 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. Split Brain Resolution in Oracle Clusterware 12c Rel 2 1. All of the business benefits of Oracle RAC and Oracle Data Guard. Oracle Net Services provide client access to the Application/Web server tier at the top of the figure, Figure 7-4 Oracle Database with Oracle RAC Architecture. What is split brain in Oracle RAC? The Oracle Data Guard broker communicates with the production database, the physical standby database, and the logical standby database. 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. (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. 1. 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. Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. As a result, equal number of database services execute on both the nodes. Oracle Data Guard provides more comprehensive data protection and its more efficient network usage allows plenty of room to grow without the expense of upgrading its network. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. 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. Starting in Oracle Database 12.1.0.2c, the new algorithm to determine the node(s) to be retained / evicted is as follows: Now I will demonstrate this new feature in an Oracle 12.1.0.2c standard 3 node cluster, using an RAC database called admindb for one of the possible factors contributing to the node weight, i.e. The sum of benefits of Oracle Clusterware with Oracle Data Guard, Best high availability, data protection, and disaster-recovery solution with scalability built in, The sum of benefits of Oracle RAC with Oracle Data Guard, Oracle Database with Oracle GoldenGateFoot3, Bidirectional replication and information management, Replica database (or databases) available for read/write use, Fast failover for computer failure and storage failure, Minimum downtime for computer or site maintenance and database and application upgrades. High availability solution with added data and disaster recovery protection. By using specialized devices, this distance can be extended to 66 kilometers. Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. 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. There is no fancy or expensive hardware required. which node first joined the cluster). It requires only a standard TCP/IP-based network link between the two computers. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. Oracle RAC One Node allows you to run one instance of an Oracle RAC database on a single node in a cluster. But 1 and 2 cannot talk to 3, and vice versa. Online Reorganization and Redefinition allows for dynamic data changes. In addition to maintaining its own disk block, CSSD processes also monitors the disk blocks maintained by the CSSD processes running in other cluster nodes. Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. Oracle RAC builds higher levels of availability on top of the standard Oracle Database features. 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. The premise of the Data Guard hub is that it provides higher utilization with lower cost. Although traditional solutions (such as backup and recovery from tape, storage-based remote mirroring, and database log shipping) can deliver some level of high availability, Oracle Data Guard provides the most comprehensive high availability and disaster recovery solution for Oracle databases. Support for heterogeneous platforms, versions, and character sets. You can allocate server resources to multiple instances using Oracle Database Resource Manager Instance Caging. For more information, see "Data Guard Support for Heterogeneous Primary and Physical Standbys in Same Data Guard Configuration" in My Oracle Support Note at, https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&id=413484.1.
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