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. The following list describes examples of Oracle Data Guard configurations using single standby databases: A national energy company uses a standby database located in a separate facility 10 miles away from its primary data center. The center frame shows the configuration during fast-start failover. (adsbygoogle=window.adsbygoogle||[]).push({}); 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 using the said resources. (See Section 7.1.5 for a complete description.). Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. Start both the services for database admindb so that serv1 executes on host01 and serv2 executes on host02. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Fast Recovery Area manages local recovery-related files. Table 7-5 compares the attainable recovery times of each Oracle high availability architecture for all types of planned downtime. 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. 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. Another possible configuration might be a testing hub consisting of snapshot standby databases. The group(cohort) with lower node member survive, in case of same number of node(s) available in each group. Corruption Prevention, Detection, and Repair detect and prevent some corruptions and lost writes. If all the sub-clusters are of the same size, the functionality has been modified as: If the sub-clusters have equal node weights, the sub-cluster with the lowest numbered node in it survives so that, in a 2-node cluster, the node with the lowest node number will survive. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. There is no fancy or expensive hardware required. These solutions are categorized into local high availability solutions that provide high availability in a single data center deployment, and disaster-recovery solutions, which are usually geographically distributed deployments that protect your applications from disasters such as floods or regional network outages. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. You can define multiple application VIPs, with generally one application VIP defined for each application running. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. There are some corruptions that cannot be addressed by automatic block repair, and for those we can rely on Data Guard failover that takes seconds to minutes. In an Oracle cluster prior to version 12.1.0.2c, when a split brain problem occurs, the node with lowest node number survives. Q39) Mention what is split brain syndrome in RAC? (For complete disaster recovery and data protection, use the architecture shown in Figure 7-8.). Oracle Data Guard Advantages Compared to Remote Mirroring Solutions. 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. Fast-Start Fault Recovery bounds and optimizes instance and database recovery times to minutes. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. Footnote6Recovery time for human errors depend primarily on detection time. Support for fine-grained, n-way multimaster, hub-and-spoke, or many-to-one replication architectures. With the Oracle Grid technologies, you can enable a high level of usage and low TCO without sacrificing business requirements. 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 Oracle Database with Oracle Clusterware (After Cold Cluster Failover). Maximum RTO for instance or node failure is in seconds. Vijay.Cherukuri-Oracle Dec 18 2011 edited Nov 5 2012. A single standby database architecture consists of the following key traits and recommendations: Standby database resides in Site B. 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. High availability benefits and workload balancing outweigh performance concerns. In a "split brain" situation, voting disk is used to determine which node (s) will survive and which node (s) will be evicted. Figure 7-9 shows the recommended MAA configuration, with Oracle Database, Oracle RAC, and Oracle Data Guard. More investment and expertise to build and maintain an integrated high availability solution is available. 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. All Oracle RAC nodes can be active by implementing multiple Oracle RAC One Node configurations for different databases. See Oracle Data Guard Broker for a detailed description of the observer. The application VIP is tied to the application by making it dependent on the application resource defined by Cluster Ready Services (CRS). To avoid splitbrain, node 2 aborted itself. 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. 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. From the entry point to an Oracle Application Server system (content cache) to the back-end layer (data sources), all the tiers that are crossed by a request can be configured in a redundant manner with Oracle Application Server. 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. Whatever the case, these Oracle RAC interview questions and answers are for you. This figure shows Oracle Database with Oracle RAC architecture for a partitioned three-node database. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. For more information, see the "Administering Oracle RAC One Node" section in the Oracle Real Application Clusters Administration and Deployment Guide. But 1 and 2 cannot talk to 3, and vice versa. Uses a private network and voting disk-based communication to detect and resolve split-brainFoot2 scenarios. Choice of RPO equal to zero (SYNC) or near-zero (ASYNC). 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 . 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. 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. To ensure data consistency, each instance of a RAC database needs to keep heartbeat with the other instances. 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. (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.). 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. However, an extended cluster cannot protect against all data corruptions or specific data failures that impact the database, or against comprehensive disasters such as earthquakes, hurricanes, and regional floods that affect a greater geographical area. 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. Now talking about split-brain concept with respect to oracle . Willing to make additional provisions for remote data protection to protect against database, data, and cluster failures and corruptions. Oracle RAC exploits the redundancy that is provided by clustering to deliver availability with n - 1 node failures in an n-node cluster. 1. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. 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. Oracle Clusterware manages the availability of both the user applications and Oracle databases. Table 7-2 recommends architectures based on your business requirements for RTO, RPO, MO, scalability, and other factors. 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. End-users connect to clusters through a public network. Rolling upgrade for system, clusterware, operating system, database, and application. Support is for single-instance databases only. These updates are discarded when the snapshot database is reconverted to a physical standby database. The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. They will enhance your knowledge and help you to emerge as the best candidate. 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 . The operation of an Oracle Clusterware cold cluster failover is depicted in Figure 7-2 and Figure 7-3. Fine control of information and data sharing are required. An architecture that combines Oracle Database with Oracle RAC is inherently a highly available system. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. You can allocate server resources to multiple instances using Oracle Database Resource Manager Instance Caging. Data Recovery Advisor provides intelligent advice and repair of different data failures, Oracle Secure Backup provides a centralized tape backup management solution. You should determine if both sites are likely to be affected by the same disaster. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. 1. After the former primary database has been repaired, the observer reestablishes its connection to that database and reinstates it as a new standby database. 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 Application Server provides high availability and disaster recovery solutions for maximum protection against any kind of failure with flexible installation, deployment, and security options. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. Rolling upgrade and patch capabilities for Oracle Clusterware with zero database downtime. 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. The SELECT statement is used to retrieve information from a database. 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. When the two data centers are located relatively close to each other, extended clusters can provide great protection for some disasters, but not all. Online Patching allows for dynamic database patches for diagnostic and interim patches. This book focuses primarily on the database high availability solutions. host01 is evicted although it has a lower node number. Oracle recommends that you create and store the local backups in the fast recovery area. host02 is retained as it has higher number of database services executing. Footnote4Database is still available, but a portion of the application connected to the failed system is temporarily affected. At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. Common messages in instance alert log are similar to: In above example, instance 2 LMD0 (pid 29940) is the receiver in IPC Send timeout. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. Zero downtime when using the provisioning capability in Oracle Enterprise Manager Grid Control. The second standby database automatically receives data from the new primary database, insuring that data is protected at all times. This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. the clusterware identifies the largest sub-cluster, and aborts all the nodes which do NOT belong to that sub-cluster. A highly available and resilient application requires that every component of the application must tolerate failures and changes. 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. Oracle Database with Oracle RAC architecture is designed primarily as a scalability and availability solution that resides in a single data center. 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. 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. Clients are connected to the logical standby database and can work with its data. As a result, equal number of database services execute on both the nodes. It requires only a standard TCP/IP-based network link between the two computers. 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. 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/. the number of database services executing on a node. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. It is based on proven Oracle high availability technologies and recommendations. 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. 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. Figure 7-3 shows the Oracle Clusterware configuration after a cold cluster failover has occurred. split brain syndrome. Where two or more instances . During normal operation, the production site services requests; in the event of a site failover or switchover, the standby site takes over the production role and all requests are routed to that site. 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. Applications scale in an Oracle RAC environment to meet increasing data processing demands without changing the application code. 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. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. the. In the figure, Node 2 is now the active instance connected to the Oracle database and servicing applications and users. Commonly, one will see messages similar to the followings in ocssd.log when split brain happens: Above messages indicate the communication from node 2 to node 1 is not working, hence node 2 only sees 1 node, but node 1 is working fine and it can see two nodes in the cluster. Network addresses are failed over to the backup node. 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. By using specialized devices, this distance can be extended to 66 kilometers. The instances monitor each other by checking "heartbeats." Both the primary and secondary sites contain Oracle Application Servers, two database instances, and an Oracle database. 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. 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. Nodes 1,2 can talk to each other. Oracle Data Guard is designed to allow businesses get something useful out of their expensive investment in a disaster-recovery site. 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. The rightmost frame shows the configuration after fast-start failover has occurred. 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. High availability functionality to manage third-party applications, Rolling release upgrades of Oracle Clusterware.
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