The term "Split-Brain" is often used to describe the scenario when two or more co-operating processes in a distributed system, typically a high availability 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 . The production database is connected over the network to the physical standby database site and the logical standby database site (the standby databases may be at the same or different sites). Support is for single-instance databases only. Oracle Clusterware cold cluster failover combined with Oracle Data Guard makes a tightly integrated solution in which failover to the secondary node in the cold cluster failover is transparent and does not require you to reconfigure the Oracle Data Guard environment or perform additional steps. A highly available and resilient application requires that every component of the application must tolerate failures and changes. Footnote1Applications (or a portion of an application) connected to the system that is being maintained may be temporarily affected. Footnote1Recovery time indicated applies to database and existing connection failover. Oracle RAC exploits the redundancy that is provided by clustering to deliver availability with n - 1 node failures in an n-node cluster. 3. The observer (thin client watchdog) resides in the application tier and monitors the availability of the primary database. Footnote8With automatic block repair, this should be the most common block corruption repair. Applications can easily mask failures to the end user. Table 7-3 Additional Capabilities of High Level Oracle High Availability Architectures, The foundation for all high availability architectures. Off-load read-only, reporting, testing and backup activities to the standby database. This chapter describes the various high availability architectures in an Oracle environment and helps you to choose the correct architecture for your organization. Section 3.4.1 describes how Oracle Clusterware is software that, when installed on servers running the same operating system, enables the servers to be bound together to operate as if they are one server, and manages the availability of user applications and Oracle databases. Oracle Clusterware provides tolerance of node failures, whereas Oracle Data Guard provides additional protection against data corruptions, lost writes, and database and site failures. 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. Site configurations are on heterogeneous platforms. This is often called the multi-master problem. See Section 7.1.3, "Oracle Database with Oracle RAC One Node" for more information. There is no fancy or expensive hardware required. Several standby databases in an Oracle RAC environment residing in a cluster of servers, called a grid server. 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. Common messages in instance alert log are similar to: In above example, instance 2 LMD0 (pid 29940) is the receiver in IPC Send timeout. 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 Syndrome, In a Oracle RAC environment all the instances/servers communicate with each other using high-speed interconnects on the private network. Split Brain Resolution in Oracle Clusterware 12c Rel 2 1. Figure 7-7 shows the production database at the primary site and multiple standby databases at secondary sites. This book focuses primarily on the database high availability solutions. 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 . Figure 7-6 Primary and Standby Databases and the Observer During Fast-Start Failover. the number of database services executing on a node. The fast-start failover has completed and the target standby database is running in the primary database role. 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 . Uses a private network and voting disk-based communication to detect and resolve split-brain Foot 2 scenarios. Oracle Flashback Technology optimizes logical failure repair. Maximum RTO for instance or node failure is in seconds. The second standby database automatically receives data from the new primary database, insuring that data is protected at all times. For example, Table 7-1 provides some insight into the probability of different outages during unplanned and planned activities. 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. Rolling upgrade for system, clusterware, operating system, CPUs, and some Oracle interim patches. The production database transmits redo data (either synchronously or asynchronously) to redo log files at the physical standby database. Online Patching allows for dynamic database patches for diagnostic and interim patches. Oracle recommends that you create and store the local backups in the fast recovery area. FAN with integrated Oracle client failover, including Java applications using UCP with Oracle RAC and Oracle Data Guard. 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. RPO is zero for cluster failover, choice of RPO equal to zero for database failover (Data Guard SYNC), or near-zero (Data Guard ASYNC). For an Oracle RAC database, each node in a cluster usually has one instance of the running Oracle software that references the database. This would lead to collision and corruption of shared data as each sub-cluster assumes ownership of shared data. 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. Configuring symmetric sites is recommended to ensure that each site can accommodate the performance and scalability requirements of the application after any role transition. We will verify that when an unequal number of database services are running on the two nodes, the node hosting the higher number of database services survives even if it has a higher node number. Rolling upgrade for system, clusterware, database, and operating system. 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. The common voting result will be: a. The script content on this page is for navigation purposes only and does not alter the content in any way. 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. What is split brain in Oracle RAC? 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. Hence, we observed that when an equal number of database services were running on both nodes, the node with lower node number (host01) survives. Many high availability architectures today use clusters alone to provide some rudimentary node redundancy and automatic node failover. Oracle RAC Split Brain Syndrome Scenerio oracle-tech Fine control of information and data sharing are required. 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. 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. 2. Oracle Clusterware provides a number of benefits over third-party clusterware. 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. Provides maximum protection from physical corruptions. The solutions introduced in this book are described in detail in the Oracle Fusion Middleware High Availability Guide. In Oracle RAC each node in the cluster is interconnected through a private interconnect. In simpler terms, in a split-brain situation, there are in a sense two (or more) separate clusters working on the same shared storage. 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. Hence, to protect the integrity of the cluster and its data, the split-brain must be resolved. All Oracle RAC nodes can be active by implementing multiple Oracle RAC One Node configurations for different databases. Oracle Clusterware: Enables you to use an entire software solution from Oracle, avoiding the cost and complexity of maintaining additional cluster software. Then, the redo data is applied from the logs to the physical standby database, which backs up the redo data to physical media. At the logical standby database, the redo data is transformed into SQL statements, which are applied to the logical standby database. 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 high availability benefits to using Oracle RAC One Node include the following: Offers better database availability than traditional cold failover solutions, Provides better virtualization for databases than hypervisor-based solutions, Enables online migration of database instances and online patching and upgrading of operating system and database software (incurring no downtime), Delivers a comprehensive, single-vendor solution, with no need to implement third-party products, Is ready to scale and upgrade to multinode Oracle RAC, Provides a standardized environment and a common toolset for both single-node and multinode Oracle database deployments, Is less expensive than cold fail over solutions or a full Oracle RAC deployment. Online Patching allows for dynamic database patching of typical diagnostic patches. These best practices are required to maximize the benefits of each architecture. All single-instance high availability features, such as the Flashback technologies and online reorganization, also apply to Oracle RAC. 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. Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. 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. 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 . The instances monitor each other by checking "heartbeats." Fast-start failover is recommended to provide automatic failover without user intervention and bounded recovery time. They will enhance your knowledge and help you to emerge as the best candidate. 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. You can configure the failed application connections to fail over to the replica. Oracle Security Features prevent unauthorized access and changes. 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. Name of the cluster: Cluster01.example.com, Number of nodes: 3 (host01, host02, host03), Instances of RAC database: admindb1 on host01. There are numerous high availability features that you can use in the Oracle Database single-instance database architecture. You can achieve the highest level of availability when using Oracle RAC and Oracle Data Guard and there is no need to make application changes to use these Oracle Database features. Furthermore, the standby databases can be used for read-only access and subsequently for reader farms, for reporting, and for testing and development. You can allocate server resources to multiple instances using Oracle Database Resource Manager Instance Caging. Oracle Data Guard Advantages Over Traditional Solutions. Section 7.1.8 describes how you can achieve the highest level of availability with Oracle RAC and Oracle Data Guard. To avoid splitbrain, node 2 aborted itself. Unlike the cold cluster model where one node is completely idle, all instances and nodes can be active to scale your application. Higher flexibilityOracle Data Guard is implemented on pure commodity hardware. Figure 7-6 shows the relationships between the primary database, target standby database, and the observer before, during, and after a fast-start failover. 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 . A single standby database architecture consists of the following key traits and recommendations: Standby database resides in Site B. These updates are discarded when the snapshot database is reconverted to a physical standby database. The following sections provide an overview of Oracle Database high availability architectures and implement the MAA best practices: Oracle Database with Oracle Clusterware (Cold Cluster Failover), Oracle Database with Oracle Real Application Clusters (Oracle RAC), Oracle Database with Oracle Clusterware and Oracle Data Guard, Oracle Database with Oracle RAC One Node and Oracle Data Guard, Oracle Database with Oracle RAC and Oracle Data Guard. 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. Split Brain: What's new in Oracle Database 12.1.0.2c? 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. Figure 7-1 Single-Node, Nonclustered Oracle Database with an Oracle ASM Instance. 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.
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