Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. Online Patching allows for dynamic database patching of typical diagnostic patches. See Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)" for more information about the best practices documentation. 1. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. For example, an Oracle Data Guard hub could include multiple databases and applications that are supported in a grid server and storage architecture. 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. With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). 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. By using specialized devices, this distance can be extended to 66 kilometers. You might choose to use Oracle GoldenGate to configure and maintain a logical copy of your production database. It also allows the storage to be laid out in a different fashion from the primary computer. The servers on which you want to run Oracle Clusterware must be running the same operating system. Oracle Data Guard transmits redo data from the primary database to the secondary site to keep the databases synchronized. 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. Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. In a split brain situation, voting disk will be used to determine which node(s) survive and which node(s) will be evicted. Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster 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. Footnote2Oracle ASM automatically rebalances stored data when disks are added or removed while the database remains online. Then this process is referred as Split Brain Syndrome. This has the potential for data corruption. At a high level, Oracle Application Server local high availability architectures include several active-active and active-passive architectures for the OracleAS middle-tier and the OracleAS Infrastructure. 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. 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. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. Oracle Data Guard Advantages Over Traditional Solutions. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. In a "split brain" situation, voting disk is used to determine which node (s) will survive and which node (s) will be evicted. The heartbeat is maintained by background processes like LMON, LMD, LMS and LCK. 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. Split Brain Condition - STOMITH STONITH fencing - dba-oracle.com Oracle Clusterware manages the availability of both the user applications and Oracle databases. 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. You should determine if both sites are likely to be affected by the same disaster. At the time of role transition, more storage and system resources can be allocated toward that application. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. 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. High Availability Architectures and Solutions - Oracle The public and private interconnects, and the Storage Area Network (SAN) are all on separate dedicated channels, with each one configured redundantly. Note, however, that the synchronous redo transport does not impose any physical distance limitation. The individual nodes are running fine and can accept user connections and work . In Oracle RAC each node in the cluster is interconnected through a private interconnect. 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. Provides maximum protection from physical corruptions. 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. which node first joined the cluster). Oracle Grid Infrastructure and Oracle RAC make use of Redundant Interconnect Usage that distributes network traffic and ensures optimal communication in the cluster. 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. 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. Oracle recommends that you use the following Oracle features to make a standalone database on a single computer available for certain failures and planned maintenance activities: Fast-Start Fault Recovery bounds and optimizes instance and database recovery times. This unique solution combines the proven Oracle Data Guard technology in Oracle Database with advanced disaster recovery technologies in the application realm to create a comprehensive disaster recovery solution for the entire application system. The following list describes examples of Oracle Data Guard configurations using single standby databases: A national energy company uses a standby database located in a separate facility 10 miles away from its primary data center. 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 group(cohort) with more cluster nodes survive Split Brain: Whats new in Oracle Database 12.1.0.2c? Rolling upgrade for system, clusterware, operating system, database, and application. Commonly, one will see messages similar to the followings in ocssd.log when split brain happens: Above messages indicate the communication from node 2 to node 1 is not working, hence node 2 only sees 1 node, but node 1 is working fine and it can see two nodes in the cluster. Logical or user failures that manipulate logical data (DMLs and DDLs). Online Reorganization and Redefinition allows for dynamic data changes. 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. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. Footnote8With automatic block repair, this should be the most common block corruption repair. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). In Oracle RAC, all the instances/servers communicate with each other using a private network. 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. Oracle RAC : understanding split brain - The Geek Diary 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. It is possible, under certain circumstances, to build and deploy an Oracle RAC system where the nodes in the cluster are separated by greater distances. 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 . 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. You can have up to 32 voting disks in your cluster. CSSD process in each RAC node maintains a heart beat in a block of size 1 OS block in a specific offset by read/write system calls (pread/pwrite), in the voting disk. Oracle RAC Interview Questions - Coherence and Split-Brain In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. The common voting result will be: a. 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 . Ina cluster, a private interconnect is used by cluster nodes to monitor each nodes status and communicate with each other. Each site is a self-contained system. Use a physical standby database if read-only access is sufficient. 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 ). Glossary - Oracle There are some corruptions that cannot be addressed by automatic block repair, and for those we can rely on Data Guard failover that takes seconds to minutes. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. The problem which could arise out of this situation is that the sane . In Oracle RAC each node in the cluster is interconnected through a private interconnect. 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. Different character sets are required between the primary database and its replicas. But 1 and 2 cannot talk to 3, and vice versa. Maximum RTO for instance or node failure is in seconds. Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. 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. If you configure a single voting disk, then you should use external mirroring to provide redundancy. Then there are two cohorts: {1, 2} and {3}. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. Top 25 Oracle RAC Interview Questions and Answers in 2023 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. These best practices are required to maximize the benefits of each architecture. 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. Maximum RTO for instance or node failure is zero for the databaseFootref1. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. 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. Fast-Start Fault Recovery bounds and optimizes instance and database recovery times to minutes. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. Filed Under: oracle, RAC Tagged With: RAC, split brain, vcs basics Communication faults, jeopardy, split brain, I/O fencing, How to Enable or Disable Veritas ODM for Oracle database 12.1.0.1, ORA-16713: The Oracle Data Guard broker command timed out When Changing LogXptMode, Managing Oracle Database Backup with RMAN (Examples included), Cron Script does not Execute as Expected from crontab Troubleshoot, Oracle SQL Script to Report Tablespace Free and Fragmentation, Beginners Guide to Flash Recovery Area in Oracle Database, How to Identify the Last and Next Refresh Dates for a Materialized View, Oracle 20c New Feature: PDB Point-in-Time Recovery or Flashback to Any Time, How to use nomodeset to Troubleshoot Boot Issues. the number of database services executing on a node. 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. Willing to make additional provisions for remote data protection to protect against database, data, and cluster failures and corruptions. Footnote1Applications (or a portion of an application) connected to the system that is being maintained may be temporarily affected. For storage migration, you are required to use both storage arrays by Oracle ASM temporarily. 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). 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 . 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. Then there are two cohorts: {1, 2} and {3}. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. Provides seamless integration with, and migration to, Oracle Real Application Clusters (Oracle RAC) and Oracle Data Guard. Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover). Node 1 is connected to Node 2 and to the Oracle database, but Node 1 is currently idle, in standby mode. It is based on proven Oracle high availability technologies and recommendations. Oracle RAC Operational Best Practices for the Cloud Created Date: Oracle High Availability Best Practice recommendations can be found in Oracle Database High Availability Best Practices and in the white papers that can be downloaded from, Table 7-4 Attainable Recovery Times for Unplanned Outages, No downtimeFootref4 if the outage is limited to one building, Hours to days if the outage affects both building. 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 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. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. Oracle Application Server provides redundancy by offering support for multiple instances supporting the same workload. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle RAC One Node database. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle One Node database. It allows you to select the table columns depending on a set of criteria. 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. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. 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. Better suited for WANsRemote mirroring solutions based on storage systems often have a distance limitation due to the underlying communication technology (Fibre Channel or ESCON (Enterprise Systems Connection)) used by the storage systems. Maximum RTO for instance or node failure is in minutes. SELECT statements might be as straightforward as selecting a few . the. Clusterware will evaluate cluster resources on implied workload 3. . The data is derived from actual user experiences and from Oracle service requests. Oracle Clusterware: Enables you to use an entire software solution from Oracle, avoiding the cost and complexity of maintaining additional cluster software. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. Table 7-5 compares the attainable recovery times of each Oracle high availability architecture for all types of planned downtime. This is often called the multi-master problem. See the high availability solutions and recommendations for Oracle Application Server, Oracle Enterprise Manager, and Oracle Applications on the MAA Web site at: Oracle Database High Availability Best Practices, Oracle Real Application Clusters Administration and Deployment Guide, Oracle Data Guard Concepts and Administration, Oracle Streams Replication Administrator's Guide, Oracle Fusion Middleware High Availability Guide, Oracle Application Server High Availability Guide, Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)", Corruption Prevention, Detection, and Repair, Online Application Maintenance and Upgrades, Description of "Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance", Section 7.1.3, "Oracle Database with Oracle RAC One Node", Description of "Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover)", Description of "Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover)", Description of "Figure 7-4 Oracle Database with Oracle RAC Architecture", Description of "Figure 7-5 Oracle RAC Extended Cluster", http://www.oracle.com/technetwork/database/clustering/overview/, Description of "Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover", Description of "Figure 7-7 Oracle Database with Oracle Data Guard on Primary and Multiple Standby Sites", Description of "Figure 7-8 Oracle Clusterware (Cold Cluster Failover) and Oracle Data Guard", Description of "Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA". 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. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. If the primary system should fail, the first standby database becomes the new primary database. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. For more information, see the "Administering Oracle RAC One Node" section in the Oracle Real Application Clusters Administration and Deployment Guide. But 1 and 2 cannot talk to 3, and vice versa. 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. RPO is zero for cluster failover, choice of RPO equal to zero for database failover (Data Guard SYNC), or near-zero (Data Guard ASYNC). Fast Recovery Area manages local recover-related files automatically. 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. 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. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. All of the business benefits of Oracle RAC. split brain syndrome. Table 7-3 Additional Capabilities of High Level Oracle High Availability Architectures, The foundation for all high availability architectures. Maximum RTO for instance or node failure is in seconds to minutes. Also, to prevent a full cluster outage if either site fails, the configuration includes a third voting disk on an inexpensive, low-end standard network file system (NFS) mounted device. 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.
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