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High Availability, Datos personales, Referencais - Coggle Diagram

- - - - Data that was committed before the crash but not yet written to the datafiles is recovered from the redo logs.
      - The roll forward phase brings the datafiles up to the point in time when the crash occurred.
      - This phase guarantees that all committed transactions are reflected in the datafiles.
      - During the roll forward phase of instance recovery, Oracle replays the committed transactions from the online redo logs. This process ensures that all changes up to the point of the crash are applied to the database.
    - - In the roll back phase of instance recovery, Oracle identifies and undoes any in-flight (uncommitted) transactions that were active at the time of the crash.
      - Uncommitted transactions are rolled back or undone to maintain data consistency.
      - This ensures that only the changes made by transactions that were committed are retained in the database.
- - - - RAID 1 (Mirroring) duplicates data on two disks, ensuring data integrity even if one disk fails.
      - RAID 5 (Striping with Parity) distributes data and parity information across multiple disks, allowing for data recovery if one disk fails.
- - - - Oracle Export (exp): This utility allows you to create a binary dump of specific Oracle database objects such as tables, schemas, or the entire database. The export file contains the database structure and data in a proprietary format.
      - Oracle Import (imp): This utility is used to import data from export files created with Oracle Export. It regenerates the database objects and data in a target database.
    - - Database Migration: You can use Export and Import to move data between databases, even on different platforms.
      - Backup and Recovery: By exporting specific data, you can have a snapshot of the database that can be used for recovery in case of data corruption or accidental deletions.
  - - - Full Backup: Exporting the entire database or specific schema for a full backup ensures that a complete copy of data is available.
      - Point-in-Time Recovery: Exported data can be used for point-in-time recovery, allowing you to restore data to a specific moment in the past.
- - - - In high availability discussions, it's crucial to quantify the availability of a system. This is often represented as a percentage
        
        Availability Percentage: It represents the portion of time a system is up and operational.
      - The availability percentage can be translated into the amount of annual downtime, which provides a clearer perspective of system reliability.
        
        Annual Downtime: This is the cumulative time in a year when a system is not operational. It's typically calculated based on the difference between 100% (full-time operation) and the availability percentage.
        
        Table 11-1: A table that translates the percentage of availability into days, minutes, and hours of annual downtime for a 365-day year.
    - - High availability requirements can vary based on business needs and operational hours.
        
        Normal Working Hours: Some organizations may prioritize availability during regular business hours (e.g., 8 a.m. to 5 p.m.). Downtime during these hours can be more disruptive and costly.
        
        24-Hour Availability: In contrast, other businesses, especially multinational companies, require 24/7 availability due to global operations.
      - Determining when availability is measured is as important as the percentage itself.
      - For example, planned downtime might make more sense after business hours to minimize the impact, reducing unplanned failures during critical business hours.