Common messages in instance alert log are similar to: In above example, instance 2 LMD0 (pid 29940) is the receiver in IPC Send timeout. Customer can designate which server(s) and resource(s) are critical 2. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. Q39) Mention what is split brain syndrome in RAC? Support for fine-grained, n-way multimaster, hub-and-spoke, or many-to-one replication architectures. Furthermore, the standby databases can be used for read-only access and subsequently for reader farms, for reporting, and for testing and development. To ensure data consistency, each instance of a RAC database needs to keep heartbeat with the other instances. Oracle Grid Infrastructure and Oracle RAC make use of Redundant Interconnect Usage that distributes network traffic and ensures optimal communication in the cluster. Then this process is referred as Split Brain Syndrome. Nodes 1,2 can talk to each other. Unlike the cold cluster model where one node is completely idle, all instances and nodes can be active to scale your application. A telecommunications provider uses asynchronous redo transport to synchronize a primary database on the West Cost of the United States, with a standby database on the East Coast, over 3,000 miles away. Support for bidirectional replication and updating anything and anywhere. 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. By reducing the combinations of software that you must coordinate and support, you can increase the manageability and availability of your system software. But 1 and 2 cannot talk to 3, and vice versa. 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. Figure 7-7 shows the production database at the primary site and multiple standby databases at secondary sites. During the process of resolving conflicts, information may be lost or become corrupted. Prior to Oracle Database 12.1.0.2c, the algorithm to determine the node (s) to be retained / evicted is as follows: If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster . 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. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. Oblivious of the existence of other cluster fragments, each sub-cluster continues to operate independently of the others. Different character sets are required between the primary database and its replicas. 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. It requires only a standard TCP/IP-based network link between the two computers. The Maximum Availability Architecture (MAA) is Oracle's best practices blueprint. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. 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 allocate server resources to multiple instances using Oracle Database Resource Manager Instance Caging. Split Brain: What's new in Oracle Database 12.1.0.2c? 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. Unlike a traditional monolithic database server that is expensive and is not flexible to changing capacity and resource demands, Oracle RAC combines the processing power of multiple interconnected computers to provide system redundancy, scalability, and high availability. So, in a two node situation both the instances will think that the other instance is down because of lack of connection. The new primary database starts transmitting redo data to the new standby database. 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. 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. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. Fast Recovery Area manages local recover-related files automatically. During normal operation, the production site services requests; in the event of a site failover or switchover, the standby site takes over the production role and all requests are routed to that site. Oracle Database with Oracle RAC on Extended Clusters. If the sub-clusters have unequal node weights, the sub-cluster having the higher weight survives so that, in a 2-node cluster, the node with the lowest node number might be evicted if it has a lower weight. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. 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. Since I will only explore the scenarios for which functionality has been modified, i.e. There is no fancy or expensive hardware required. Name of the cluster: Cluster01.example.com, Number of nodes: 3 (host01, host02, host03), Instances of RAC database: admindb1 on host01. Split Brain Syndrome in RAC. The system resources can be dynamically allocated and deallocated depending on various priorities. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. 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. 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. (For complete disaster recovery and data protection, use the architecture shown in Figure 7-8.). Oracle Database High Availability Architectures, Choosing the Correct High Availability Architecture, Integrating Application Server High Availability, Integrating High Availability for All Applications. The common voting result will be: a. This book focuses primarily on the database high availability solutions. 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. 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. Off-load read-only, reporting, testing and backup activities to the standby database. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. Corruption Prevention, Detection, and Repair detect and prevent some corruptions and lost writes. 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. It also gives users complete control over the routing of change records from the primary database to a replica database. This architecture is identical to the single-standby database architecture that was described in Section 7.1.5.1, except that there are multiple standby databases in the same Oracle Data Guard configuration. The application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). 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. Applications can easily mask failures to the end user. As the result, 1 or more instance(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. Logical or user failures that manipulate logical data (DMLs and DDLs). Rolling upgrade for system, clusterware, database, and operating system. Maximum RTO for data corruption, cluster, database, or site failures is in seconds to minutes. 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. 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. 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. Another possible configuration might be a testing hub consisting of snapshot standby databases. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. In a typical example, the maximum distance between the systems connected in a point-to-point fashion and running synchronously can be only 10 kilometers. The operation of an Oracle Clusterware cold cluster failover is depicted in Figure 7-2 and Figure 7-3. The public and private interconnects, and the Storage Area Network (SAN) are all on separate dedicated channels, with each one configured redundantly. For virtualization, Oracle RAC One Node with Oracle VM increases the benefit of Oracle VM with the high availability and scalability of Oracle RAC. Split Brain Syndrome Basic Concept in Oracle RAC Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. 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 . Oracle RAC Split Brain Syndrome Scenerio. These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. 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. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. 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. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. Similar to using Oracle Data Guard in SQL Apply mode, Oracle GoldenGate can capture database changes, propagate them to destinations, and apply the changes at these destinations. 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. Where two or more instances . Oracle Data Guard transmits redo data from the primary database to the secondary site to keep the databases synchronized. An exception is undropping a table, which is literally instantaneous regardless of detection time. Oracle RAC - Wikipedia 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. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. 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. Oracle Flashback Technology optimizes logical failure repair. 008 - How Node Membership Happens in RAC? - What is Voting Disk & Split Glossary - Oracle 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. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. Provides maximum protection from physical corruptions. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. 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. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. The rightmost frame shows the configuration after fast-start failover has occurred. Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. 2. An architecture that combines Oracle Database with Oracle RAC is inherently a highly available system. PDF Oracle Clusterware 12c Release 2 Technical Overview Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. Although both types of solutions provide high availability, active-active solutions generally offer higher scalability and faster failover, although they tend to be more expensive. The combination of Oracle RAC and Oracle Data Guard provide the most comprehensive architecture for reducing downtime for scheduled outages and preventing, detecting, and recovering from unscheduled outages. The center frame shows the configuration during fast-start failover. Many high availability architectures today use clusters alone to provide some rudimentary node redundancy and automatic node failover. 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. 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 . 1. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. Oracle Data Guard is a high availability and disaster-recovery solution that provides very fast automatic failover (referred to as fast-start failover) in database failures, node failures, corruption, and media failures. Oracle RAC One Node allows you to run one instance of an Oracle RAC database on a single node in a cluster. Better performanceOracle Data Guard only transmits write I/Os to the redo log files of the primary database, whereas remote mirroring solutions must transmit these writes and every write I/O to data files, additional members of online log file groups, archived redo log files, and control files. At the snapshot standby database redo data is received, but it is not applied until the snapshot standby database is reconverted to a physical standby database. Willing to make additional provisions for remote data protection to protect against database, data, and cluster failures and corruptions. pagespeed.lazyLoadImages.overrideAttributeFunctions(); Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. The problem which could arise out of this situation is that the sane . Dynamic Resource Provisioning allows for dynamic system changes. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. 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. They will enhance your knowledge and help you to emerge as the best candidate. Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. Node 1 is connected to Node 2 and to the Oracle database, but Node 1 is currently idle, in standby mode. Online Patching allows for dynamic database patches for diagnostic and interim patches. 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.
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