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Oracle Tutorials: How to configure high availability in oracle?

April 26, 2023 Leave a Comment

What is high availability?

High availability (HA) refers to the ability of a system or service to remain operational and accessible to users, even in the event of hardware or software failures, system upgrades, or other disruptions.

In other words, a high availability system is designed to minimize or eliminate downtime, ensuring that critical business operations can continue uninterrupted. This is particularly important in industries where downtime can have significant financial or operational consequences, such as finance, healthcare, and e-commerce.

To achieve high availability, systems are typically designed with redundancy and failover mechanisms, which allow for seamless transition between components in the event of a failure. This might involve multiple servers, storage systems, or network connections, all of which work together to ensure continuous operation and availability of the system.

How high availability work for Database?

High availability for databases typically involves implementing technologies and practices that ensure that the database remains available and operational in the event of a failure or disruption.

Some common approaches to achieving high availability for databases include:

  1. Database Replication: This involves creating one or more copies of the database, which are kept in sync with the master database in real-time. If the master database fails, one of the replicas can be promoted to take its place, ensuring that users can continue accessing the database without interruption.
  2. Clustering: This involves grouping multiple servers together to act as a single logical unit, with each server sharing the load of processing requests. If one server fails, the others can take over its workload, ensuring that there is no interruption in service.
  3. Automated Failover: This involves using software to automatically detect when a component of the database environment fails, and then automatically switching to a redundant component to ensure continuous operation.
  4. Load Balancing: This involves distributing database requests across multiple servers to ensure that no single server becomes overloaded, which can lead to downtime.

How Oracle Database works?

Oracle Database is a relational database management system that is used to store, manage, and manipulate large amounts of data. Here’s how Oracle Database works:

  1. Storage: Data is stored in tablespaces, which are logical storage structures that are divided into datafiles. Datafiles are made up of physical files that are stored on disk.
  2. Memory: Oracle Database uses the System Global Area (SGA) to cache frequently accessed data and to manage database operations. The SGA consists of several components, including the buffer cache, shared pool, and redo log buffer.
  3. Processes: Oracle Database runs several background processes that perform a variety of functions, including managing memory, monitoring system performance, and managing datafiles and tablespaces.
  4. SQL Processing: Oracle Database uses Structured Query Language (SQL) to retrieve and manipulate data. SQL statements are processed by the Oracle Database SQL engine, which generates an execution plan based on the SQL statement and data dictionary statistics.
  5. Security: Oracle Database provides several security features, including user authentication, role-based access control, and encryption.
  6. Backup and Recovery: Oracle Database includes tools for backing up and recovering data, including Recovery Manager (RMAN), which allows for efficient backups and point-in-time recovery, and Oracle Flashback, which provides a quick way to recover from user errors.
  7. Scalability: Oracle Database is designed to be highly scalable, with the ability to handle large amounts of data and users. It can be run on a single server or on a cluster of servers using Oracle Real Application Clusters (RAC).

Oracle Architecture

Oracle architecture refers to the underlying structure of the Oracle database system, which is made up of several components that work together to store and manage data. Here are the main components of the Oracle architecture:

  1. Instance: The instance is the set of memory structures and background processes that manage the database. It includes the System Global Area (SGA) which stores data and control information, and the Program Global Area (PGA) which stores data for individual sessions.
  2. Database: The database is the physical storage structure where the data is stored. It includes datafiles, control files, and redo logs.
  3. Tablespaces: The tablespace is a logical storage structure within the database, where database objects such as tables, indexes, and views are stored.
  4. Segments: A segment is a set of extents that are allocated for storing a specific type of data, such as tables or indexes.
  5. Extents: An extent is a group of contiguous data blocks that are allocated for storing a specific segment.
  6. Data Blocks: A data block is the smallest unit of storage in an Oracle database, and is typically 8KB in size.
  7. Redo Logs: Redo logs are used to record all changes made to the database. They are essential for recovering the database in the event of a failure.
  8. Control Files: Control files contain metadata about the database, including the database name, file locations, and backup information.

What are Options for high availability in oracle?

Oracle provides several options for high availability that are designed to ensure that the database remains operational and accessible to users, even in the event of hardware or software failures. Here are some of the main options for high availability in Oracle:

  1. Oracle Real Application Clusters (RAC): RAC is a clustered database technology that allows multiple servers to work together as a single system. This provides both scalability and high availability, as data and processing can be distributed across multiple servers, and the system can continue to operate even if one or more servers fail.
  2. Data Guard: Data Guard is a disaster recovery and high availability solution that uses standby databases to provide failover and data protection. The standby database is kept in sync with the primary database, so that in the event of a failure, the standby database can be quickly activated to take over operations.
  3. Oracle GoldenGate: GoldenGate is a replication technology that can be used to keep multiple databases in sync in real-time. This can be used for disaster recovery, high availability, and data integration.
  4. Automatic Storage Management (ASM): ASM is a storage management tool that provides automatic disk rebalancing, automatic failover, and online disk reconfiguration. It is designed to simplify storage management and improve availability.
  5. Oracle Clusterware: Clusterware is a clustering software that provides node monitoring, failover management, and application fencing. It is used to manage the Oracle Cluster Database and other Oracle high availability products.
Rajesh Kumar
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