what is split brain in oracle rac
Ina cluster, a private interconnect is used by cluster nodes to monitor each nodes status and communicate with each other. The figure shows users making local updates to the snapshot standby database. For example : Applications scale in an Oracle RAC environment to meet increasing data processing demands without changing the application code. 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. 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. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. 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). Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. Split Brain Syndrome in RAC. Split Brain Syndrome Basic Concept in Oracle RAC. Oracle Clusterware manages the availability of both the user applications and Oracle databases. Then this process is referred as Split Brain Syndrome. Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. Oracle RAC exploits the redundancy that is provided by clustering to deliver availability with n - 1 node failures in an n-node cluster. 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. The servers on which you want to run Oracle Clusterware must be running the same operating system. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. . In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover. But 1 and 2 cannot talk to 3, and vice versa. 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). The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. Their strategy further mitigates risk by maintaining multiple standby databases, each implemented using a different architecturesRedo Apply and SQL Apply. We will verify that when an equal number of database services are running on both nodes, the node with lower node number (host01) survives. Logical or user failures that manipulate logical data (DMLs and DDLs). Rolling upgrade for system, clusterware, database, and operating system. 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. Oracle RAC builds higher levels of availability on top of the standard Oracle Database features. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. Footnote2The portion of any application connected to the failed system is temporarily affected. Different character sets are required between the primary database and its replicas. However, when the data centers are located more than 66 kilometers apart, you must use a series of repeaters and converters from third-party vendors. Disaster recovery solutions typically set up two homogeneous sites, one active and one passive. Fast Recovery Area manages local recovery-related files. You can configure the failed application connections to fail over to the replica. 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. 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. Flexible and automated high availability solutions ensure that applications you deploy on Oracle Application Server meet the required availability to achieve your business goals. Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA. 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. The voting result is similar to clusterware voting result. the number of database services executing on a node. 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. Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. Data Recovery Advisor diagnoses persistent (on disk) data failures, presents appropriate repair options, and runs repair operations at your request. As the result, 1 or more instance(s) will be evicted. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle RAC One Node database. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. Footnote3For qualified one-off patches only. The following list summarizes the advantages of using Oracle Data Guard compared to using remote mirroring solutions: Better network efficiencyWith Oracle Data Guard, only the redo data needs to be sent to the remote site and the redo data can be compressed to provide even greater network efficiency. See Section 7.2 for a comparison of the different architectures and highlights of the benefits and considerations. the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. These updates are discarded when the snapshot database is reconverted to a physical standby database. 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. With Database Server Grid and Database Storage Grid (described in Section 5.2 and Section 5.3), you can build standby database and testing hubs that use a pool of system resources. 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. Now talking about split-brain concept with respect to oracle . With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. 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. Section 7.1.8 describes how you can achieve the highest level of availability with Oracle RAC and Oracle Data Guard. Now talking about split-brain concept with respect to oracle RAC systems, it occurs when the instance 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. Please enroll for the Oracle DBA Interview Question Course.https://learnomate.org/courses/oracle-dba-interview-question/Use DBA50 to get 50% discountPlease s. 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. 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. 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". Network connection changes and other site-specific failover activities may lengthen overall recovery time. Online Patching allows for dynamic database patching of typical diagnostic patches. For example, you can put the files on different disks, volumes, file systems, and so on. In Oracle RAC each node in the cluster is interconnected through a private interconnect. 817202 Mar 1 2016 edited Mar 2 2016. 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. Q39) Mention what is split brain syndrome in RAC? With Oracle Clusterware, you can provide a cold cluster failover to protect an Oracle Database instance from a system or server failure. End-users connect to clusters through a public network. 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. Uses a private network and voting disk-based communication to detect and resolve split-brain Foot 2 scenarios. The second standby database automatically receives data from the new primary database, insuring that data is protected at all times. 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. Controlfile is used similarly to voting disk in clusterware layer to determine which instance(s) survive and which instance(s) evict. Maximum RTO for instance or node failure is in minutes. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. The logical standby database may contain additional indexes and materialized views. 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. Note, however, that the synchronous redo transport does not impose any physical distance limitation. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect. RAC Split Brain Syndrome. Higher ROIBusinesses must obtain maximum value from their IT investments, and ensure that no IT infrastructure is sitting idle. However, remote mirroring solutions affect DBWR process performance because they subject all DBWR process write I/O's to network and disk I/O induced delays inherent to synchronous, zero-data-loss configurations. Oracle Flashback Technology optimizes logical failure repair. 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. As per Split brain syndrome in Oracle RAC in case of inter-connect failures the master node will evict other/dead nodes . Clients are connected to the logical standby database and can work with its data. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. Oracle Automatic Storage Management (Oracle ASM) and Oracle Automatic Storage Management Cluster File System (Oracle ACFS) tolerate storage failures and optimize storage performance and usage. See Section 7.1.3, "Oracle Database with Oracle RAC One Node" for more information. All of the business benefits of Oracle RAC. Oracle Data Guard Advantages Over Traditional Solutions. 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. Another possible configuration might be a testing hub consisting of snapshot standby databases. 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. The sum of benefits of Oracle Clusterware with Oracle Data Guard, Best high availability, data protection, and disaster-recovery solution with scalability built in, The sum of benefits of Oracle RAC with Oracle Data Guard, Oracle Database with Oracle GoldenGateFoot3, Bidirectional replication and information management, Replica database (or databases) available for read/write use, Fast failover for computer failure and storage failure, Minimum downtime for computer or site maintenance and database and application upgrades. 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 . host01 is retained as it has a lower node number. Start both the services for database admindb so that equal number of database services execute on both the nodes. 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. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). The SELECT statement is used to retrieve information from a database. Figure 7-3 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). The fast-start failover has completed and the target standby database is running in the primary database role. Footnote6Recovery time for human errors depend primarily on detection time. 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. These figures show how you can use the Oracle Clusterware framework to make both Oracle Database and your custom applications highly available. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. Following the execution of a SELECT statement, a tabular result is held in a result table (called a result set). 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 center frame shows the configuration during fast-start failover. The operation of an Oracle Clusterware cold cluster failover is depicted in Figure 7-2 and Figure 7-3. In Oracle Database 11g Release 2 (11.2), Oracle RAC One Node or Oracle RAC is the preferred solution over Oracle Clusterware (Cold Cluster Failover) because it is a more complete and feature-rich solution. 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 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. These redundant configurations provide increased availability either through a distributed workload, through a failover setup, or both. The Oracle Data Guard broker communicates with the production database, the physical standby database, and the logical standby database. If the primary system should fail, the first standby database becomes the new primary database. 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. 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. This is called Split Brain. Oracle Enterprise Management support for Oracle ASM and Oracle ACFS, Grid Plug and Play, Cluster Resource Management, Oracle Clusterware and Oracle RAC Provisioning and patching, Figure 7-4 shows Oracle Database with Oracle RAC architecture. It allows you to select the table columns depending on a set of criteria. When you move the Oracle RAC One Node instance to the newly resized Oracle VM node, you can dynamically increase any limits programmed with Resource Manager Instance Caging. Whatever the case, these Oracle RAC interview questions and answers are for you. In the figure, the configuration is operating in normal mode in which Node 1 is the active instance connected to Oracle Database that is servicing applications and users. For high availability, Oracle recommends that you have a minimum of three voting disks. 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. 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. 1. Fast Recovery Area manages local recover-related files automatically. 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. 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. Although traditional solutions (such as backup and recovery from tape, storage-based remote mirroring, and database log shipping) can deliver some level of high availability, Oracle Data Guard provides the most comprehensive high availability and disaster recovery solution for Oracle databases. Footnote3The initial investment to build a robust solution is well worth the long-term flexibility and capabilities that Oracle GoldenGate delivers to meet specific business requirements. Oracle Data Guard transmits redo data from the primary database to the secondary site to keep the databases synchronized. 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. 2. 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. pagespeed.lazyLoadImages.overrideAttributeFunctions(); 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. The problem which could arise out of this situation is that the sane . It supports bidirectional replication, data transformations, subsetting, custom apply functions, and heterogeneous platforms. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. Then there are two cohorts: {1, 2} and {3}. But 1 and 2 cannot talk to 3, and vice versa. The group(cohort) with lower node member survive, in case of same number of node(s) available in each group. host02 is retained as it has higher number of database services executing. In a split brain situation, voting disk is used to determine which node(s) will survive and which node(s) will be evicted. With the snapshot standby database hub, you can use the combined storage and server resources of a grid instead of building and managing individual servers for each application. Since I will only explore the scenarios for which functionality has been modified, i.e. Footnote2Rolling upgrades with Oracle Data Guard incur minimal downtime. 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. For example, you can use your favorite application query in the database check action. There are three typical causes of corruption: Maximum RTO for instance or node failure is zero for the databaseFootref1. 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. However, starting from Oracle Database 12.1.0.2c, the node with higher weight will survive during split brain resolution. For example, if a stray write occurs to a disk, or there is a corruption in the file system, or the host bus adaptor corrupts a block as it is written to disk, then a remote mirroring solution may propagate this corruption to the disaster-recovery site.