split brain syndrome. 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. Applications scale in an Oracle RAC environment to meet increasing data processing demands without changing the application code. You can have up to 32 voting disks in your cluster. As the result, 1 or more instance(s) will be evicted. The second standby database automatically receives data from the new primary database, insuring that data is protected at all times. 1. 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. 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. The probability of failing over all databases at the same time is unlikely. Ina cluster, a private interconnect is used by cluster nodes to monitor each nodes status and communicate with each other. It also gives users complete control over the routing of change records from the primary database to a replica database. 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. Maximum RTO for instance or node failure is in seconds. Table 7-5 compares the attainable recovery times of each Oracle high availability architecture for all types of planned downtime. Oracle RAC - Wikipedia There are three typical causes of corruption: Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect. End-users connect to clusters through a public network. It allows you to select the table columns depending on a set of criteria. Then there are two cohorts: {1, 2} and {3}. 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 Application Server provides redundancy by offering support for multiple instances supporting the same workload. which node first joined the cluster). 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. Online Patching allows for dynamic database patches for diagnostic and interim patches. Applications can easily mask failures to the end user. 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. All of the business benefits of Oracle RAC. The system resources can be dynamically allocated and deallocated depending on various priorities. The servers on which you want to run Oracle Clusterware must be running the same operating system. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. (See Section 7.1.5 for a complete description.). 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. 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. Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. 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. By reducing the combinations of software that you must coordinate and support, you can increase the manageability and availability of your system software. The instances monitor each other by checking "heartbeats." If you configure a single voting disk, then you should use external mirroring to provide redundancy. The common voting result will be: a. Section 7.1.8 describes how you can achieve the highest level of availability with Oracle RAC and Oracle Data Guard. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. RAC Split Brain Syndrome. Provides maximum protection from physical corruptions. Split Brain: What's new in Oracle Database 12.1.0.2c? 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. 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. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. Oracle Secure Backup provides a centralized tape backup management solution. In a split brain situation, voting disk will be used to determine which node(s) survive and which node(s) will be evicted. 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. host01 is retained as it has a lower node number. 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). 008 - How Node Membership Happens in RAC? - What is Voting Disk & Split Oracle RAC Operational Best Practices for the Cloud Created Date: 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. For example, you can use your favorite application query in the database check action. 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. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. 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. It is based on proven Oracle high availability technologies and recommendations. If your VM is sized too small, you can migrate the Oracle RAC One instance to another larger Oracle VM node in the cluster (using the online database relocation utility) or move the Oracle RAC One instance to another Oracle VM node, and then resize the Oracle VM. 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. Oracle recommends that you create and store the local backups in the fast recovery area. (For complete disaster recovery and data protection, use the architecture shown in Figure 7-8.). Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover). Logical or user failures that manipulate logical data (DMLs and DDLs). Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. Oracle Enterprise Manager support for patch application simplifies software maintenance. Oracle Database with Oracle RAC on Extended Clusters. A single standby database architecture consists of the following key traits and recommendations: Standby database resides in Site B. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle RAC One Node database. Network addresses are failed over to the backup node. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. RPO is zero for cluster failover, choice of RPO equal to zero for database failover (Data Guard SYNC), or near-zero (Data Guard ASYNC). Footnote2Oracle ASM automatically rebalances stored data when disks are added or removed while the database remains online. Typically, this is not possible with remote mirroring solutions. The premise of the Data Guard hub is that it provides higher utilization with lower cost. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. Footnote4Tables can be reorganized online using the DBMS_REDEFINITION package. 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. 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. 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. Zero downtime when using the provisioning capability in Oracle Enterprise Manager Grid Control. The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. Q39) Mention what is split brain syndrome in RAC? Controlfile is used similarly to voting disk in clusterware layer to determine which instance(s) survive and which instance(s) evict. 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. 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. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. It also allows the storage to be laid out in a different fashion from the primary computer. Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA. 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. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. High availability functionality to manage third-party applications, Rolling release upgrades of Oracle Clusterware. Vijay.Cherukuri-Oracle Dec 18 2011 edited Nov 5 2012. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. Simulate loss of connectivity between two nodes. (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.). Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. the. 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. Rolling upgrade for system, clusterware, database, and operating system. The group(cohort) with lower node member survive, in case of same number of node(s) available in each group. This is often called the multi-master problem. 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. . An Oracle RAC database is connected to three instances on different nodes. host02 is retained as it has higher number of database services executing. Support for bidirectional replication and updating anything and anywhere. Clients are connected to the logical standby database and can work with its data. PDF Oracle Clusterware 12c Release 2 Technical Overview Split Brain Syndrome | Oracle Database Internal Mechanism 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. 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. 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. Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). 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. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. The clusters that are typical of Oracle RAC environments can provide continuous service for both planned and unplanned outages. 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 . For physical standby databases, this solution: Supports very high primary database throughput. 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. Online Patching allows for dynamic database patching of typical diagnostic patches. 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 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. 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. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. Now talking about split-brain concept with respect to oracle RAC systems, it occurs when the instance They will enhance your knowledge and help you to emerge as the best candidate. An exception is undropping a table, which is literally instantaneous regardless of detection time. There is no fancy or expensive hardware required. Flexible propagation and management of data, transactions, and events. For more information, see the "Administering Oracle RAC One Node" section in the Oracle Real Application Clusters Administration and Deployment Guide. Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Maximum RTO for data corruption, cluster, database, or site failures is in seconds to minutes. During the process of resolving conflicts, information may be lost or become corrupted. Higher ROIBusinesses must obtain maximum value from their IT investments, and ensure that no IT infrastructure is sitting idle. This would lead to collision and corruption of shared data as each sub-cluster assumes ownership of shared data. 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. Split Brain in RAC Database | RAC DBA Training - YouTube Table 7-4 shows the recovery time (including detection and client failover time) of an integrated Oracle client, whenever relevant. High availability benefits and workload balancing outweigh performance concerns. Oracle Flashback Technology optimizes logical failure repair. 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 Application Server instances can be installed in either site as long as they do not interfere with the instances in the disaster recovery setup. The figure shows users making local updates to the snapshot standby database. Figure 7-7 shows the production database at the primary site and multiple standby databases at secondary sites. Table 7-5 Attainable Recovery Times for Planned Outages, System change - Dynamic Resource Provisioning. The SELECT statement is used to retrieve information from a database. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. There are numerous high availability features that you can use in the Oracle Database single-instance database architecture. Node 1 is connected to Node 2 and to the Oracle database, but Node 1 is currently idle, in standby mode. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). RAC Split Brain Syndrome - Devops Tutorials 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. Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. For more information see the MAA white paper "Rapid Oracle RAC One Node Standby Deployment" at. Nodes 1,2 can talk to each other. Oracle Data Guard Advantages Over Traditional Solutions. After the former primary database has been repaired, the observer reestablishes its connection to that database and reinstates it as a new standby database. Use a physical standby database if read-only access is sufficient. Suppose there are 3 nodes in the following situation. 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.
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