CHAPTER 11 Oracle and High Availability

CHAPTER 11 Oracle and High Availability

1. What Is High Availability?

   • Protect and provide timely access to data when necessary
   • When the database is unavailable, we refer to that as downtime. Of course
   • Accessibility to data via web-based solutions means that database failures can have a broad impact

2. The System Stack and Availability

   • There are many different causes of unplanned downtime. You can prevent some very easily, while others require significant investments in site infrastructure, including soft‐ ware, servers, storage, networks, and appropriate employee skills.
   • Different strategies and solutions exist for achieving high availability for each of the system components

3. Server Hardware, Storage, and Database Instance Failure

   • The failure of servers or storage hosting a database can be one of the most abrupt causes of unplanned downtime.
   • A server may crash because of hardware problems, such as the failure of a power supply, or because of software problems, such as a process that begins to consume all the machine’s CPU resources

4. What Is Instance Recovery?

   • When you restart an Oracle instance after a failure, Oracle detects that a crash occurred using information in the control file and the headers of the database files.
     • All committed transactions will be recovered.
     • In-flight transactions will be rolled back or undone.

5. Phases of Instance Recovery

   • Instance recovery has two phases: roll forward and roll back.
     • The redo logs contain a recording of all the physical changes made to the database as a result of transactional activity, both committed and uncommitted.
   • When the roll forward phase is finished, all the changes for committed and uncom‐ mitted transactions have been reproduced.

6. Protecting Against System Failure

   • Providing component redundancy
   • Deploying Data Guard to provide an alternate site in case of primary site failure
   • Deploying Real Application Clusters for database continuity in the event of failure of an instance
   • Deploying application continuity or Transparent Application Failover software services

7. Component Redundancy

   • As basic protection, the various hardware components that make up the Oracle Data‐base server
     • Fault-tolerance, as the name implies, allows the overall hardware system to continue to operate even if one of its components fails.
     • Disk drives, Disk controllers, Flash memory

8. Disk Redundancy

   • Protection from disk failure is usually accomplished using RAID (Redundant Array of Inexpensive Disks) concepts. The use of redundant storage has become common for systems of all sizes and types for two primary reasons

9. Site and Computer Server Failover

   • The Oracle Database will recover automatically from a system crash. Automatic recov‐ ery protects data integrity, critical in a relational database, but also causes some down‐ time as the Oracle Database recovers.

10. Oracle Data Guard and Site Failures

    • Data Guard is an Oracle-recommended MAA solution that is used to recover databases from site and storage failures as well as data corruption. It is included with the Enterprise Edition of Oracle and supports database configurations for physical standby (an MAA best practice), snapshot standby for testing, and logical standby to reduce planned downtime.

11. Oracle GoldenGate and Replication

    • An alternative for guarding against site and computer failures that cause unplanned downtime is to implement client and application failover leveraging log-based change data capture and replication software, such as Oracle’s GoldenGate.

12. Real Application Clusters and Instance Failures

    • Real Application Clusters (RAC) provides an Oracle-recommended MAA solution for instance or computer failures. With RAC, the Oracle database is spread across multiple nodes and each node has an active Oracle instance. Clients can connect to any of the instances to access the same database.

13. Oracle Transparent Application Failover

    • Transparent Application Failover (TAF) provides seamless migration of users’ sessions from one Oracle instance to another.
    • use TAF to mask the failure of an instance for transparent high availability or for migration of users from a highly active instance to a less active one.

14. Point-in-Time Recovery

    • Point-in-time datafile recovery enables a DBA to restore the datafiles for the Oracle database and apply redo information up to a specific time or System Change Number (SCN).

15. Nombre: Juan Manuel Figueroa Solís Carnet: 2018139700 Universidad: I.T.C.R Curso: IC4302 Bases de Datos 2 Título: Lectura 6 Fecha: 04/10 /21 Profesor:Erick Hernández Bonilla Grupo: 40

Bilder und Dateien der Mindmap