Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. 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. Table 7-4 shows the recovery time (including detection and client failover time) of an integrated Oracle client, whenever relevant. 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. Since I will only explore the scenarios for which functionality has been modified, i.e. Oracle RAC : understanding split brain - The Geek Diary Nodes 1,2 can talk to each other. An Oracle RAC database is connected to three instances on different nodes. 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. 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. You might choose to use Oracle GoldenGate to configure and maintain a logical copy of your production database. 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. Provides maximum protection from physical corruptions. The problem which could arise out of this situation is that the sane . split brain syndrome. Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. Nodes 1,2 can talk to each other. Site configurations are on heterogeneous platforms. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. 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. Maximum RTO for data corruption, cluster, database, or site failures is in seconds to minutes. For more information see the MAA white paper "Rapid Oracle RAC One Node Standby Deployment" at. Oracle Clusterware provides a number of benefits over third-party clusterware. Oracle GoldenGate can capture changes at a source database, and the captured changes can be propagated asynchronously to replica databases. By using specialized devices, this distance can be extended to 66 kilometers. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. 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 . This chapter describes the various high availability architectures in an Oracle environment and helps you to choose the correct architecture for your organization. For high availability, Oracle recommends that you have a minimum of three voting disks. Then there are two cohorts: {1, 2} and {3}. Footnote4Tables can be reorganized online using the DBMS_REDEFINITION package. Willing to make additional provisions for remote data protection to protect against database, data, and cluster failures and corruptions. Thus, compared to Oracle Data Guard, a remote mirroring solution must transmit each change many more times to the remote site. Database scalability beyond one instance or node. 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. 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 . Split Brain Syndrome Basic Concept in Oracle RAC. 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. Support for heterogeneous platforms, versions, and character sets. 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. 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. 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. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. 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 . What is Voting Disk & Split Brain Syndrome in RAC For virtualization, Oracle RAC One Node with Oracle VM increases the benefit of Oracle VM with the high availability and scalability of Oracle RAC. 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. The basic function of a cold cluster failover is to monitor a database instance running on a server, and if a failure is detected, to restart the instance on a spare server in the cluster. Furthermore, the standby databases can be used for read-only access and subsequently for reader farms, for reporting, and for testing and development. Split Brain Condition - STOMITH STONITH fencing - dba-oracle.com 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 . Top 25 Oracle RAC Interview Questions and Answers in 2023 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. Typically, this is not possible with remote mirroring solutions. 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 number of database services executing on a node. The data is derived from actual user experiences and from Oracle service requests. Oracle Data Guard Advantages Over Traditional Solutions. For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. (See Section 7.1.5 for a complete description.). Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. 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. A highly available and resilient application requires that every component of the application must tolerate failures and changes. the number of database services executing on a node. After the former primary database has been repaired, the observer reestablishes its connection to that database and reinstates it as a new standby database. Fast-start failover is recommended to provide automatic failover without user intervention and bounded recovery time. 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. Hi Guru's. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). 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). If the node running your Oracle RAC One Node becomes overloaded, you can relocate the instance to another node in the cluster using the online database relocation utility (srvctl relocate database), with no downtime for application users. Node 1 is connected to Node 2 and to the Oracle database, but Node 1 is currently idle, in standby mode. 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. Flexible propagation and management of data, transactions, and events. 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. Oracle RAC Split Brain Syndrome Scenerio. For example, if the primary database fails over to one of the standby databases in the Data Guard hub, the new primary database acquires more system and storage resources while the testing resources may be temporarily starved. Q39) Mention what is split brain syndrome in RAC? Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. Suppose there are 3 nodes in the following situation. You should adopt the MAA best practices to achieve the optimal recovery time and configuration. 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. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). To ensure data consistency, each instance of a RAC database needs to keep heartbeat with the other instances. For example, you can put the files on different disks, volumes, file systems, and so on. Section 7.1.8 describes how you can achieve the highest level of availability with Oracle RAC and Oracle Data Guard. 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. In previous releases, technologies like bonding or trunking were used to make use of redundant networks for the interconnect. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. 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. 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. But 1 and 2 cannot talk to 3, and vice versa. What is split brain in Oracle RAC? - pehdk.afphila.com Footnote8With automatic block repair, this should be the most common block corruption repair. This functionality is available starting with Oracle Database 11g Release 2 (11.2.0.2). host01 is evicted although it has a lower node number. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. 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 clusterware identifies the largest sub-cluster, and aborts all the nodes which do NOT belong to that sub-cluster. With Oracle Clusterware, . 1. Providing application-specific failure detection means Oracle Clusterware can fail over not only during the obvious cases such as when the instance is down, but also in the cases when, for example, an application query is not meeting a particular service level. All Oracle RAC nodes can be active by implementing multiple Oracle RAC One Node configurations for different databases. See Section 7.2 for a comparison of the different architectures and highlights of the benefits and considerations. 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. Online Reorganization and Redefinition allows for dynamic data changes. Longer detection time usually leads to longer recovery time required to repair the appropriate transactions. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. 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. Support is for single-instance databases only. Then this process is referred as Split Brain Syndrome. Starting from 12.1.0.2, during split brain resolution, the new algorithm followed to decide the nodes to be evicted/retained is as follows: Fortnightly newsletters help sharpen your skills and keep you ahead, with articles, ebooks and opinion to keep you informed. Prior to Oracle Database 12.1.0.2c, the algorithm to determine the node(s) to be retained / evicted is as follows: However, starting from 12.1.0.2c, in case of split brain, some improvement has been made to node eviction algorithm. 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. pagespeed.lazyLoadImages.overrideAttributeFunctions(); 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 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. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. 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. Logical or user failures that manipulate logical data (DMLs and DDLs). If you configure a single voting disk, then you should use external mirroring to provide redundancy. This book focuses primarily on the database high availability solutions. This is called Split Brain. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. 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. Oracle Database with Oracle GoldenGate provides granularity and control over what is replicated and how it is replicated. 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. 2. Provides seamless integration with, and migration to, Oracle Real Application Clusters (Oracle RAC) and Oracle Data Guard. This has the potential for data corruption. If the sub-clusters are of the different sizes, the functionality is same as earlier i.e. The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. See Section 7.1.3, "Oracle Database with Oracle RAC One Node" for more information. A nationally recognized insurance provider in the U.S. maintains two standby databases in the same Oracle Data Guard configuration: one physical standby and one logical standby database. Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. Footnote6Recovery time for human errors depend primarily on detection time. 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. Table 7-3 Additional Capabilities of High Level Oracle High Availability Architectures, The foundation for all high availability architectures. 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. Maximum RTO for data corruptions, database, or site failures is in seconds to minutes. Footnote3For qualified one-off patches only. The SELECT statement is used to retrieve information from a database. 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. Unlike the cold cluster model where one node is completely idle, all instances and nodes can be active to scale your application. 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. Oracle RAC on an extended cluster provides greater availability than a local Oracle RAC cluster, but an extended cluster may not completely fulfill the disaster recovery requirements of your organization. mysql - Split brain scenario - RAC and PXC - Database Administrators 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. The probability of failing over all databases at the same time is unlikely. Higher ROIBusinesses must obtain maximum value from their IT investments, and ensure that no IT infrastructure is sitting idle. The active site is generally called the production site, and the passive site is called the standby site. Why is it like that? In a split brain situation, voting disk will be used to determine which node(s) survive and which node(s) will be evicted. It allows you to select the table columns depending on a set of criteria. 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). Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. 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. Chapter 2 describes how the high availability requirements for the business plus its allotted budget determine the appropriate architecture. To provide this transparent failover capability, Oracle Clusterware requires a virtual IP (VIP) address for each node in the cluster. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). Oracle Secure Backup provides a centralized tape backup management solution. Footnote2The portion of any application connected to the failed system is temporarily affected. There are numerous high availability features that you can use in the Oracle Database single-instance database architecture. This architecture is referred to as an extended cluster. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. This section contains the following topics: Oracle Application Server High Availability Architectures, High Availability Services in Oracle Application Server. The clusters that are typical of Oracle RAC environments can provide continuous service for both planned and unplanned outages. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. 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. See the high availability solutions and recommendations for Oracle Application Server, Oracle Enterprise Manager, and Oracle Applications on the MAA Web site at: Oracle Database High Availability Best Practices, Oracle Real Application Clusters Administration and Deployment Guide, Oracle Data Guard Concepts and Administration, Oracle Streams Replication Administrator's Guide, Oracle Fusion Middleware High Availability Guide, Oracle Application Server High Availability Guide, Section 1.5, "Roadmap to Implementing the Maximum Availability Architecture (MAA)", Corruption Prevention, Detection, and Repair, Online Application Maintenance and Upgrades, Description of "Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance", Section 7.1.3, "Oracle Database with Oracle RAC One Node", Description of "Figure 7-2 Oracle Database with Oracle Clusterware (Before Cold Cluster Failover)", Description of "Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover)", Description of "Figure 7-4 Oracle Database with Oracle RAC Architecture", Description of "Figure 7-5 Oracle RAC Extended Cluster", http://www.oracle.com/technetwork/database/clustering/overview/, Description of "Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover", Description of "Figure 7-7 Oracle Database with Oracle Data Guard on Primary and Multiple Standby Sites", Description of "Figure 7-8 Oracle Clusterware (Cold Cluster Failover) and Oracle Data Guard", Description of "Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA". Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. An Oracle RAC extended cluster is an architecture that provides extremely fast recovery from a site failure and allows for all nodes, at all sites, to actively process transactions as part of single database cluster. 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. Maximum RTO for instance or node failure is in seconds. 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. As the result, 1 or more instance(s) will be evicted. 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. 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. Oracle Data Guard is designed to allow businesses get something useful out of their expensive investment in a disaster-recovery site. 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. The split brain syndrome and its affects and how it has been managed in oracle is mentioned below. Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). 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. 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. Better resilience and data protectionOracle Data Guard ensures much better data protection and data resilience than remote mirroring solutions. In Oracle RAC, all the instances/servers communicate with each other using a private network. The rightmost frame shows the configuration after fast-start failover has occurred. 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. Oblivious of the existence of other cluster fragments, each sub-cluster continues to operate independently of the others.