MSAMM
Back to course

Oracle Apps DBA: Keeping E-Business Suite Alive · Module 3 · The database itself

Redo: the reason recovery is possible

Lesson 26 of 184 · 2 min

What redo records, why it is written BEFORE the change, and what archiving it buys you. MODULE 5 DEPENDS ENTIRELY ON THIS. Redo is a record of every change made to the database, written as the change happens. Not the data, and not the SQL — a description of the physical modification, sufficient to reproduce it exactly. AND IT IS WRITTEN BEFORE THE CHANGED DATA REACHES DISK, WHICH IS THE PROPERTY THE WHOLE THING RESTS ON. A commit is not a promise that your data has been written to a datafile; it is a promise that a REDO RECORD describing it is safely on disk. So if the instance dies a second later, the change is not in the datafiles and is recoverable from redo — which is exactly what happens automatically on the next startup after an abort or a crash. THAT IS WHY A COMMIT IS FAST WHILE…

The full lesson is part of the course

The video, the complete written lesson and the module quiz are included in Oracle Apps DBA: Keeping E-Business Suite Alive, with a certificate on completion and a fourteen-day refund window.

See the course and enrol9 free lessons

Get the free lessons by email

We will email you a link to every free lesson in this course. No account needed, and one message only.

In this module: Module 3 · The database itself

  1. 1Instance and database: two different things
  2. 2Starting and stopping, properly
  3. 3Tablespaces and datafiles
  4. 4Redo: the reason recovery is possible
  5. 5Archive log mode, and the day it was off
  6. 6Undo, and read consistency
  7. 7Parameters, and the ones that matter here
  8. 8The data dictionary, as a diagnostic tool
  9. 9Reading an error you have never seenFree preview
  10. 10What breaks: four database-tier failures
  11. 11Lab briefing · Stop it, start it, break it