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. To protect against site failures, the MAA recommends that Oracle RAC and Oracle Data Guard reside on separate systems (clusters) and data centers. When a database is started, Oracle Database allocates a memory area called the System Global Area (SGA) and starts one or more Oracle Database processes. 2. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. Table 7-2 High Availability Architecture Recommendations. Maximum RTO for instance or node failure is in seconds to minutes. The system resources can be dynamically allocated and deallocated depending on various priorities. 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. Hi Guru's. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). 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. For example, you can put the files on different disks, volumes, file systems, and so on. Suppose there are 3 nodes in the following situation. 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. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. 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. Fast-Start Fault Recovery bounds and optimizes instance and database recovery times to minutes. 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. Start both the services for database admindb so that equal number of database services execute on both the 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.). 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. Rolling upgrade for system, clusterware, database, and operating system. Use a physical standby database if read-only access is sufficient. Oracle Database High Availability Best Practices for information about configuring Oracle Database 11g with Oracle RAC on extended clusters, White papers about extended (stretch) clusters and about using standard NFS to support a third voting disk on an extended cluster configuration at http://www.oracle.com/technetwork/database/clustering/overview/. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. 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. 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. Oracle Clusterware manages the availability of both the user applications and Oracle databases. Support for bidirectional replication and updating anything and anywhere. 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. This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. All of the business benefits of Oracle RAC and Oracle Data Guard. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). 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. 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. Split brain scenario - RAC and PXC. Flexible propagation and management of data, transactions, and events. For more information, see Oracle Data Guard Concepts and Administration or the Oracle Streams Replication Administrator's Guide. 2. Customer can designate which server(s) and resource(s) are critical 2. 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. It allows you to select the table columns depending on a set of criteria. But 1 and 2 cannot talk to 3, and vice versa. Whatever the case, these Oracle RAC interview questions and answers are for you. Now talking about split-brain concept with respect to oracle RAC systems, it occurs when the instance If it takes seconds to detect a malicious DML or DLL transaction, it typically only requires seconds to flash back the appropriate transactions. 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. Logical or user failures that manipulate logical data (DMLs and DDLs). Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. Oracle Clusterware provides a number of benefits over third-party clusterware. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. 3. If the sub-clusters are of the different sizes, the functionality is same as earlier i.e. If you configure a single voting disk, then you should use external mirroring to provide redundancy. 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 ). With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. For example, an Oracle Data Guard hub could include multiple databases and applications that are supported in a grid server and storage architecture. In the figure, Node 2 is now the active instance connected to the Oracle database and servicing applications and users. 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. For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. 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. RPO is zero for cluster failover, choice of RPO equal to zero for database failover (Data Guard SYNC), or near-zero (Data Guard ASYNC). This figure shows Oracle Database with Oracle RAC architecture for a partitioned three-node database. The following list describes some implementations for a multiple standby database architecture: Continuous and transparent disaster or high availability protection if an outage occurs at the primary database or the targeted standby database, Regional reporting or reader databases for better response time, Synchronous redo transport that transmits to a more local standby database, and asynchronous redo transport that transmits to a more remote standby database for optimum levels of performance and data protection, Transient logical standby databases (described in Section 3.6.3) for minimal downtime rolling upgrades, Test and development clones using snapshot standby databases (described in Section 3.6.4), Scaling the configuration by creating additional logical standby databases or snapshot standby databases. Fast-start failover is recommended to provide automatic failover without user intervention and bounded recovery time. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). Applications scale in an Oracle RAC environment to meet increasing data processing demands without changing the application code. 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. Site configurations are on heterogeneous platforms. Oracle recommends that you use automatic undo management with sufficient space to attain your desired undo retention guarantee, enable Oracle Flashback Database, and allocate sufficient space and I/O bandwidth in the fast recovery area. See Oracle Data Guard Broker for a detailed description of the observer. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). Node 1 is connected to Node 2 and to the Oracle database, but Node 1 is currently idle, in standby mode. 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. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. (See Section 7.1.5 for a complete description.). 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. You can allocate server resources to multiple instances using Oracle Database Resource Manager Instance Caging. This is often called the multi-master problem. 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. 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. The term "Split-Brain" is often used to describe the scenario when two or more co-operating processes in a distributed system, typically a high availability 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 . Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. Clusterware will evaluate cluster resources on implied workload 3. . The problem which could arise out of this situation is that the sane . The Oracle Data Guard broker communicates with the production database, the physical standby database, and the logical standby database. Split Brain Syndrome in RAC. Split Brain: Whats new in Oracle Database 12.1.0.2c? Rolling upgrade for system, clusterware, operating system, database, and application. The servers on which you want to run Oracle Clusterware must be running the same operating system. Oracle Database is a single-instance, standalone (noncluster) database and it is the foundation for all high availability architectures. Oracle Secure Backup provides a centralized tape backup management solution. 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. Footnote4Tables can be reorganized online using the DBMS_REDEFINITION package. You should determine if both sites are likely to be affected by the same disaster. 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.

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