Fault Isolation During Recovery

The recovery procedures, known simply as “recovery,” rebuild the server’s databases from the transaction logs.

The recovery isolation mode setting controls how recovery behaves when it detects corrupt data while reversing or reapplying a transaction in a database.

If an index is marked as suspect, the system administrator can repair this by dropping and re-creating the index.

The ability to isolate only the suspect pages while bringing the rest of the database online provides a greater degree of flexibility in dealing with data corruption. You can diagnose problems, and sometimes correct them, while most of the database remains accessible to users. You can assess the extent of the damage and schedule emergency repairs or reload for a convenient time.

Recovery fault isolation applies only to user databases. Recovery always takes a system database entirely offline if it has any corrupt pages. You cannot recover a system database until you have repaired or removed all of its corrupt pages.

• Persistence of Offline Pages
  Suspect pages that you have taken offline remain offline when you restart the server. Information about offline pages is stored in master.dbo.sysattributes.
• Configuring Recovery Fault Isolation
  When SAP ASE is installed, the default recovery isolation mode is databases, which marks a database as suspect and takes the entire database offline if it detects any corrupt pages.
• Getting Information About Offline Databases and Pages
  Use sp_listsuspect_db to see which databases have offline pages.
• Bringing Offline Pages Online
  Use sp_forceonline_db to make all the offline pages in a database accessible, and use sp_forceonline_page to make an individual offline page accessible.
• Index-Level Fault Isolation for Data-Only-Locked Tables
  When pages of an index for a data-only-locked table are marked as suspect during recovery, the entire index is taken offline.
• Side Effects of Offline Pages
  Databases with offline pages include restrictions.
• Recovery Strategies Using Recovery Fault Isolation
  Strategies for returning a database with suspect pages to a consistent state while users are accessing it include reloading the database, or repairing it.
• Assessing the Extent of Corruption
  You can sometimes use recovery fault isolation to assess the extent of corruption by forcing recovery to run and examining the number of pages marked suspect and the objects to which they belong.