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Oracle 11g Database Fault Diagnosability Infrastructure can help to prevent, detect, diagnose and solve problems.

Diagnostic data is stored in the Automatic Diagnostic Repository (ADR), which is a file based repository outside the database.  It can later be retrieved by incident number and analyzed.

Two main concepts are as follows:
1. A Problem: a critical error in the database,such as ORA-00600, ...etc
    Each problem has a problem key, which is a text string describing the problem.

2. An Incident: a single occurence of a problem.
     When a problem occurs couple times, an incident is created for each occurrence.
     Incidents are timestamped and tracked in the ADR.
     Each incident is identified by a numeric incident ID that is unique within the 
     ADR.  Once an incident happens, the database will make an entry in the alert log, 
     sent an incident to OEM, collect first-failure diagnostic data into dump
     files  concerning incident, and store the incident dumps in an ADR directory
     created for that incident.

ADR Base is found in the new 11g  database parameter named "diagnostic_dest", which replaces background_dump_dest and user_dump_dest old initialization parameters that are deprecated.

The structure for ADR directory is shown below: