In addition to maintaining its own disk block, CSSD processes also monitors the disk blocks maintained by the CSSD processes running in other cluster nodes. A world-recognized e-commerce site uses multiple standby databasesa mix of both physical and logical databasesboth for disaster recovery and to scale out read performance by provisioning multiple logical standby databases using SQL Apply. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). The probability of failing over all databases at the same time is unlikely. Oracle Database is a single-instance, standalone (noncluster) database and it is the foundation for all high availability architectures. It also gives users complete control over the routing of change records from the primary database to a replica database. Furthermore, operational practices across role transitions are simplified when the sites are symmetric. host01 is evicted although it has a lower node number. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. Why is it like that? This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. High availability functionality to manage third-party applications, Rolling release upgrades of Oracle Clusterware. Oracle Security Features prevent unauthorized access and changes. Split Brain Syndrome: In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. When the processes of the distributed system rejoin together it is possible that they have conflicting views of system state or resource ownerships. 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. Oracle Clusterware: Enables you to use an entire software solution from Oracle, avoiding the cost and complexity of maintaining additional cluster software. The cold cluster failover solution with Oracle Clusterware provides these additional advantages over a basic database architecture: Automatic recovery of node and instance failures in minutes, Automatic notification and reconnection of Oracle integrated clientsFoot3, Ability to customize the failure detection mechanism. host01 is retained as it has a lower node number. Oracle GoldenGate can capture data changes at the primary database or downstream at a replica database, thus enabling users to build hub-and-spoke network configurations that can support hundreds of replica databases. 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. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). 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. Let say 2 node RAC configuration node 1 is defined as master node (by some parameter like load and others) incase of network failures node 1 will terminate node 2 . 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. A highly available application must analyze every component that affects the application, including the network topology, application server, application flow and design, systems, and the database configuration and architecture. Fast-Start Fault Recovery bounds and optimizes instance and database recovery times to minutes. 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/. These updates are discarded when the snapshot database is reconverted to a physical standby database. However, if a remote mirroring solution is used for data protection, typically you must mirror the database files, the online redo log, the archived redo logs, and the control file. Then this process is referred as Split Brain Syndrome. 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. An Oracle RAC database is connected to three instances on different nodes. This has the potential for data corruption. Check that only two nodes (host01 and host02) are active and host01 has lower node number: Create two singleton services for the RAC database admindb: Verify that admindb is the only database in the cluster having its instances executing on host01 and host02. Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. Online Reorganization and Redefinition allows for dynamic data changes. For more information about constructing multiple-source replication environments, see the Oracle GoldenGate documentation. If the fast recovery area is on the source volume that is remotely mirrored, then you must also remotely mirror the flashback logs. 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. With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. This is often called the multi-master problem. (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.). Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). All of the business benefits of Oracle RAC and Oracle Data Guard. 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)), Zero downtime with Grid Control provisioning, Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patchesFoot1, Database Grid with site failure protection, Simplest high availability, data protection, and disaster-recovery solution, Automatic and fast failover for computer failure, storage failure, data corruption, for configured ORA- errors or conditions and database failures, Rolling upgrade for system, clusterware, database, and operating systemFoot2, Ability to off-load backups to the standby database, Ability to off-load read and reporting workload to the standby database. 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 ). (adsbygoogle=window.adsbygoogle||[]).push({}); The biggest risk following a Split-Brain event is the potential for corrupting system state. They will enhance your knowledge and help you to emerge as the best candidate. The active site is generally called the production site, and the passive site is called the standby site. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. Maximum RTO for instance or node failure is in minutes. In Oracle RAC each node in the cluster is interconnected through a private interconnect. 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. The system resources can be dynamically allocated and deallocated depending on various priorities. Oracle RAC builds higher levels of availability on top of the standard Oracle Database features. sub-clusters are of equal size, I have shut down one of the nodes so that there are only 2 active nodes in the cluster. 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. 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. The fast-start failover has completed and the target standby database is running in the primary database role. Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. 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. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. Oracle Data Guard provides more comprehensive data protection and its more efficient network usage allows plenty of room to grow without the expense of upgrading its network. 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. The problem which could arise out of this situation is that the sane . The group(cohort) with more cluster nodes survive It allows you to select the table columns depending on a set of criteria. You should adopt the MAA best practices to achieve the optimal recovery time and configuration. Figure 7-7 shows the production database at the primary site and multiple standby databases at secondary sites. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. 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. If the primary database uses the asynchronous redo transport, configure your maximum data loss tolerance or the Oracle Data Guard broker's FastStartFailoverLagLimit property to meet your business requirements. the number of database services executing on a node. Footnote4Database is still available, but a portion of the application connected to the failed system is temporarily affected. Footnote6Recovery time for human errors depend primarily on detection time. 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 figures show how you can use the Oracle Clusterware framework to make both Oracle Database and your custom applications highly available. Oracle RAC Split Brain Syndrome Scenerio. When the two data centers are located relatively close to each other, extended clusters can provide great protection for some disasters, but not all. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. Check that only two nodes (host01 and host02) are active and host01 has lower node number, Create two singleton services for the RAC database admindb. Each site is a self-contained system. Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. Table 7-3 identifies the additional capabilities provided by the architectures that build on Oracle Database and attempts to label each architecture with its greatest strengths. An architecture that combines Oracle Database with Oracle RAC is inherently a highly available system. Thus, we observed that when unequal number of database services are running on the two nodes, the node with higher number of database services survives even though it has a higher node number. 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. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. 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. 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. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. 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 operate independently of each other. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. 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. 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. The rightmost frame shows the configuration after fast-start failover has occurred. 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. Oracle GoldenGate is optimized for replicating data. Customer can designate which server(s) and resource(s) are critical 2. 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). Corruption Prevention, Detection, and Repair detect and prevent some corruptions and lost writes. Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover). 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. RAC Split Brain Syndrome. For storage migration, you are required to use both storage arrays by Oracle ASM temporarily. Then this process is referred as Split Brain Syndrome. For more information, see Oracle Data Guard Concepts and Administration or the Oracle Streams Replication Administrator's Guide. 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. 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. Suppose there are 3 nodes in the following situation. Oracle Clusterware provides a number of benefits over third-party clusterware. The voting result is similar to clusterware voting result. If your business does not require the scalability and additional high availability benefits provided by Oracle RAC, but you still need all the benefits of Oracle Data Guard and cold cluster failover, then Oracle Database with Oracle Clusterware and Oracle Data Guard is a good compromise architecture. With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. 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. 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. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. 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. Split Brain Syndrome Basic Concept in Oracle RAC. Fine control of information and data sharing are required. 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. Oracle Flashback Technology optimizes logical failure repair. Split Brain: Whats new in Oracle Database 12.1.0.2c? Now talking about split-brain concept with respect to oracle RAC systems, it occurs when the instance Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle RAC One Node database. SELECT statements might be as straightforward as selecting a few . The data is derived from actual user experiences and from Oracle service requests. 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. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. 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. Figure 7-8 Oracle Clusterware (Cold Cluster Failover) and Oracle Data Guard, The application servers on the secondary site are connected to the WAN traffic manager by a dotted line to indicate that they are not actively processing client requests at this time. Maximum RTO for instance or node failure is in seconds to minutes. This book focuses primarily on the database high availability solutions. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. Oracle GoldenGate can capture changes at a source database, and the captured changes can be propagated asynchronously to replica databases. 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. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. 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)). 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. As per Split brain syndrome in Oracle RAC in case of inter-connect failures the master node will evict other/dead nodes . High availability solution with added data and disaster recovery protection. Footnote2The portion of any application connected to the failed system is temporarily affected. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. These best practices are required to maximize the benefits of each architecture. Since I will only explore the scenarios for which functionality has been modified, i.e. The center frame shows the configuration during fast-start failover. Oracle Clusterware manages the availability of both the user applications and Oracle databases. The production database is connected over the network to the physical standby database site and the logical standby database site (the standby databases may be at the same or different sites). See Oracle Data Guard Broker for a detailed description of the observer. Network addresses are failed over to the backup node. For example, you can put the files on different disks, volumes, file systems, and so on. A single standby database architecture consists of the following key traits and recommendations: Standby database resides in Site B. Nodes 1,2 can talk to each other. Furthermore, the standby databases can be used for read-only access and subsequently for reader farms, for reporting, and for testing and development. With Oracle Clusterware, you also define an application VIP so that users can access the application independently of the node in the cluster where the application is running. This is because corruptions introduced on the production database probably can be mirrored by remote mirroring solutions to the standby site, but corruptions are eliminated by Oracle Data Guard. There are three typical causes of corruption: In Oracle RAC, all the instances/servers communicate with each other using a private network. This section summarizes the advantages of the different high availability architectures and provides guidelines for you to choose the correct high availability architecture for your business. 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. This is called Split Brain. 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. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. For more information, see "Data Guard Support for Heterogeneous Primary and Physical Standbys in Same Data Guard Configuration" in My Oracle Support Note at, https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&id=413484.1. At the time of role transition, more storage and system resources can be allocated toward that application. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. 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. 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. 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. Online Patching allows for dynamic database patching of typical diagnostic patches. 12) Mention what is split brain syndrome in RAC? You can have up to 32 voting disks in your cluster. split brain syndrome. If the sub-clusters are of the different sizes, the functionality is same as earlier i.e. Dynamic Resource Provisioning allows for dynamic system changes. Common messages in instance alert log are similar to: In above example, instance 2 LMD0 (pid 29940) is the receiver in IPC Send timeout. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. 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. Q39) Mention what is split brain syndrome in RAC? In a "split brain" situation, voting disk is used to determine which node (s) will survive and which node (s) will be evicted. There is no fancy or expensive hardware required. Section 7.1.8 describes how you can achieve the highest level of availability with Oracle RAC and Oracle Data Guard. Communication among the nodes is optimized by means of Redundant Interconnect Usage (without requiring the use of bonding or other technologies) to provide stability, reliability, and scalability. Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. End-users connect to clusters through a public network. 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. Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. During the process of resolving conflicts, information may be lost or become corrupted. Then there are two cohorts: {1, 2} and {3}. Oracle Secure Backup provides a centralized tape backup management solution. 817202 Mar 1 2016 edited Mar 2 2016. Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. 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. Footnote4Tables can be reorganized online using the DBMS_REDEFINITION package.