SELECT statements might be as straightforward as selecting a few . Another possible configuration might be a testing hub consisting of snapshot standby databases. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. If zero data loss is required with minimum performance impact on the primary database, then the best practice is to locate the secondary site within 200 miles of the primary database. Each site is a self-contained system. It requires only a standard TCP/IP-based network link between the two computers. 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. As per Split brain syndrome in Oracle RAC in case of inter-connect failures the master node will evict other/dead nodes . Fast Recovery Area manages local recovery-related files. 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. When the two data centers are located relatively close to each other, extended clusters can provide great protection for some disasters, but not all. Note, however, that the synchronous redo transport does not impose any physical distance limitation. 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. 12) Mention what is split brain syndrome in RAC? See Section 7.2 for a comparison of the different architectures and highlights of the benefits and considerations. High availability solution with added data and disaster recovery protection. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). Oracle RAC builds higher levels of availability on top of the standard Oracle Database features. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. 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. Uses a private network and voting disk-based communication to detect and resolve split-brain Foot 2 scenarios. Oracle RAC Split Brain Syndrome Scenerio. 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 data is derived from actual user experiences and from Oracle service requests. For more information, see Oracle Data Guard Concepts and Administration or the Oracle Streams Replication Administrator's Guide. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. But 1 and 2 cannot talk to 3, and vice versa. Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. 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 recommends that you create and store the local backups in the fast recovery area. 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. The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. 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. Figure 7-1 shows a basic, single-node Oracle Database that includes an Oracle ASM instance.Foot1 This architecture incorporates several high availability features, including Flashback Database, Online Redefinition, Recovery Manager, and Oracle Secure Backup. The center frame shows the configuration during fast-start failover. Oracle Database with Oracle RAC architecture provides the following benefits over a traditional monolithic database server and the cold cluster failover model: Flexibility to increase processing capacity using commodity hardware without downtime or changes to the application, Ability to tolerate and quickly recover from computer and instance failures (measured in seconds), Optimized communication in the cluster over redundant network interfaces, without using bonding or other technologies. 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 ). Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. 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. Oracle Database with Oracle RAC on Extended Clusters. The group(cohort) with lower node member survive, in case of same number of node(s) available in each group. Recovery Manager (RMAN) optimizes local repair of data failures. This is often called the multi-master problem. High availability benefits and workload balancing outweigh performance concerns. 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 . 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. 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. For more information see the MAA white paper "Rapid Oracle RAC One Node Standby Deployment" at. Off-load read-only, reporting, testing and backup activities to the standby database. You can configure Oracle GoldenGate with Oracle Data Guard to provide protection for the individual databases in the configuration. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. The recommended high availability and disaster-recovery architectures that use Oracle Data Guard are described in the following sections: Overview of Single Standby Database Architectures, Overview of Multiple Standby Database Architectures. Several standby databases in an Oracle RAC environment residing in a cluster of servers, called a grid server. Oracle Database is a single-instance, standalone (noncluster) database and it is the foundation for all high availability architectures. Support for bidirectional replication and updating anything and anywhere. 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. Oracle RAC One Node provides relocation of Oracle RAC primary and standby databases configured with Oracle Data Guard (This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2)). An infrastructure services provider to the telecommunication industry uses a single standby database located over 400 miles away from the primary database configured for synchronous redo transport, enabling zero-data-loss failover for maximum data protection and high availability. Suppose there are 3 nodes in the following situation. Their strategy further mitigates risk by maintaining multiple standby databases, each implemented using a different architecturesRedo Apply and SQL Apply. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. The application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). Split Brain Syndrome Basic Concept in Oracle RAC. Footnote1Architectures for which the MO is high might require additional time and expertise to build and maintain, but offer increased flexibility and capabilities required to meet specific business requirements. Q39) Mention what is split brain syndrome in RAC? 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. Furthermore, the standby databases can be used for read-only access and subsequently for reader farms, for reporting, and for testing and development. Network connection changes and other site-specific failover activities may lengthen overall recovery time. 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, if the extended cluster configuration is set up properly, it can protect against disasters such as a local power outage, an airplane crash, or a flooded server room. Then there are two cohorts: {1, 2} and {3}. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. For example, Table 7-1 provides some insight into the probability of different outages during unplanned and planned activities. Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. The Oracle Application Server High Availability Guide describes the following high availability services in Oracle Application Server in detail: Process death detection and automatic restart. 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. Footnote3Recovery time consists largely of the time it takes to restore the failed system. In a non-RAC Oracle database, a single instance accesses a single database. Table 7-4 shows the recovery time (including detection and client failover time) of an integrated Oracle client, whenever relevant. Since I will only explore the scenarios for which functionality has been modified, i.e. What is split brain in Oracle RAC? New requests are accepted after the Split-Brain event and then performed on potentially corrupted system state (thus potentially corrupting system state even further). 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. For example, an Oracle Data Guard hub could include multiple databases and applications that are supported in a grid server and storage architecture. Automatic block repair may be possible, thus eliminating any downtime in an Oracle Data Guard configuration. Node 1 is connected to Node 2 and to the Oracle database, but Node 1 is currently idle, in standby mode. 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.
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