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. Figure 7-9 Oracle Database with Oracle RAC and Oracle Data Guard - MAA. This scenario enables the provider to use existing data centers that are geographically isolated, offering a unique level of high availability. 2. 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. Simulate loss of connectivity between two nodes. By using specialized devices, this distance can be extended to 66 kilometers. Split Brain Syndrome in RAC. This has the potential for data corruption. Whatever the case, these Oracle RAC interview questions and answers are for you. A single standby database architecture consists of the following key traits and recommendations: Standby database resides in Site B. the number of database services executing on a node. For high availability, Oracle recommends that you have a minimum of three voting disks. Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously while accessing a single database, thus providing clustering. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. For example : Customer can designate which server(s) and resource(s) are critical 2. 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 servers on which you want to run Oracle Clusterware must be running the same operating system. Common messages in instance alert log are similar to: In above example, instance 2 LMD0 (pid 29940) is the receiver in IPC Send timeout. Another possible configuration might be a testing hub consisting of snapshot standby databases. Fast Recovery Area manages local recover-related files automatically. SELECT statements might be as straightforward as selecting a few . 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. For data resident in Oracle databases, Oracle Data Guard, with its built-in zero-data-loss capability, is more efficient, less expensive, and better optimized for data protection and disaster recovery than traditional remote mirroring solutions. Table 7-2 High Availability Architecture Recommendations. 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. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Oracle Real Application Cluster (RAC) is a unique technology that offers software for high availability and clustering in an Oracle database environment. Fast-start failover is recommended to provide automatic failover without user intervention and bounded recovery time. If the sub-clusters are of the different sizes, the functionality is same as earlier i.e. A global manufacturing company used Oracle Data Guard to replace storage-based remote mirroring and maintain a standby database at its recovery site 50 miles away from the primary site. Provides read-only access to synchronized standby database and fast incremental backups to off-load production. Use a physical standby database if read-only access is sufficient. Footnote3Recovery time consists largely of the time it takes to restore the failed system. 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. Footnote4Tables can be reorganized online using the DBMS_REDEFINITION package. Now talking about split-brain concept with respect to oracle . Recovery Manager (RMAN) optimizes local repair of data failures. Split brain scenario - RAC and PXC. 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). 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. For availability reasons, the Oracle database is a single database that is mirrored at both of the sites. 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. Furthermore, operational practices across role transitions are simplified when the sites are symmetric. Although using Oracle GoldenGate might require additional work, it offers increased flexibility that might be necessary to meet specific business requirements. These best practices are required to maximize the benefits of each architecture. The operation of an Oracle Clusterware cold cluster failover is depicted in Figure 7-2 and Figure 7-3. If the sub-clusters are of the different sizes, the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. In a split brain situation, voting disk will be used to determine which node(s) survive and which node(s) will be evicted. Although cold cluster failover is not shown in Figure 7-8, you can configure it by adding a passive node on the secondary site. You might choose to use Oracle GoldenGate to configure and maintain a logical copy of your production database. Footnote2The portion of any application connected to the failed system is temporarily affected. 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 Data Guard Advantages Over Traditional Solutions. 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. These figures show how you can use the Oracle Clusterware framework to make both Oracle Database and your custom applications highly available. Nodes 1,2 can talk to each other. 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. 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. 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. The heartbeat is maintained by background processes like LMON, LMD, LMS and LCK. Figure 7-8 shows an Oracle Clusterware and Oracle Data Guard architecture that consists of a primary and a secondary site. The configuration can be an active-active configuration using Oracle Application Server Cluster or an active-passive configuration using Oracle Application Server Cold Cluster Failover. 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. 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. Split brain syndrome occurs when the instances in a RAC fails to connect or ping to each other via the private interconnect. Any of these processes experience IPC Send time out will incur communication reconfiguration and instance eviction to avoid split brain. For more information about constructing multiple-source replication environments, see the Oracle GoldenGate documentation. 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. pagespeed.lazyLoadImages.overrideAttributeFunctions(); Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. With either the active-active or the active-passive category, multiple solutions exist that differ in ease of installation, cost, scalability, and security. This is often called the multi-master problem. Footnote5Storage failures are prevented by using Oracle ASM with mirroring and its automatic rebalance capability. Provides seamless integration with, and migration to, Oracle Real Application Clusters (Oracle RAC) and Oracle Data Guard. 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. The system resources can be dynamically allocated and deallocated depending on various priorities. c. Some improvement has been made to ensure node(s) with lower load survive in case the eviction is caused by high system load. The figure shows users making local updates to the snapshot standby database. An exception is undropping a table, which is literally instantaneous regardless of detection time. Fine control of information and data sharing are required. The center frame shows the configuration during fast-start failover. Node 2 is connected to Node 1 and to Oracle Database, but it is currently standby mode. Fully supports Oracle Data Guard. 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. 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. 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. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. 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. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. 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. The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. 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. If the sub-clusters have unequal node weights, the sub-cluster having the higher weight survives so that, in a 2-node cluster, the node with the lowest node number might be evicted if it has a lower weight. Oracle RAC exploits the redundancy that is provided by clustering to deliver availability with n - 1 node failures in an n-node cluster. It allows you to select the table columns depending on a set of criteria. 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. Fast Recovery Area manages local recovery-related files. Figure 7-2 shows a configuration that uses Oracle Clusterware to extend the basic Oracle Database architecture and provide cold cluster failover. Hi Guru's. I go through blogs mentioning what exactly a Split brain syndrome is ( Theoretical Part). the clusterware identifies the largest sub-cluster, and aborts all the nodes which do. 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. Online Application Maintenance and Upgrades with Edition-based redefinition allows an application's database objects to be changed without interrupting the application's availability. Any database in a Data Guard configuration, whether a primary or standby database, can be an Oracle One Node database. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. Then this process is referred as Split Brain Syndrome. What Is 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)). Suppose there are 3 nodes in the following situation. 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 . 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. This private network interface or interconnect are redundant and are only used for inter-instance oracle data block transfers. 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 Oracle Application Server High Availability Guide describes the following high availability services in Oracle Application Server in detail: Process death detection and automatic restart. Figure 7-1 shows a basic, single-node Oracle Database that includes an Oracle ASM instance.Foot1 This architecture incorporates several high availability features, including Flashback Database, Online Redefinition, Recovery Manager, and Oracle Secure Backup. It is based on proven Oracle high availability technologies and recommendations. Then there are two cohorts: {1, 2} and {3}. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. It also allows the storage to be laid out in a different fashion from the primary computer. In Oracle RAC each node in the cluster is interconnected through a private interconnect. Flexible propagation and management of data, transactions, and events. In this article I will explore this new feature for one of the possible factors contributing to the node weight, i.e. The group(cohort) with lower node member survive, in case of same number of node(s) available in each group. Oracle recommends that you use automatic undo management with sufficient space to attain your desired undo retention guarantee, enable Oracle Flashback Database, and allocate sufficient space and I/O bandwidth in the fast recovery area. Better resilience and data protectionOracle Data Guard ensures much better data protection and data resilience than remote mirroring solutions. Configurations and data must be synchronized regularly between the two sites to maintain homogeneity. (For complete disaster recovery and data protection, use the architecture shown in Figure 7-8.). To maintain the standby site for failover, not only must the standby site contain homogeneous installations and applications, data and configurations must also be synchronized constantly from the production site to the standby site.
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