Automatic Diagnostic Repository (ADR)

Starting with Oracle 11g R1, traditional *_DUMP_DEST parameters are ignored and the trace location is decided based on DIAGNOSTIC_DEST parameter. If this parameter is not set explicitly, it defaults to ORACLE_BASE environment variable if this is set, if this is not set, then it defaults to ORACLE_HOME/log.

DIAGNOSTIC_DEST is the ADR root directory also known as ADR base.

Each instance's diagnostic data is stored in its own ADR home directory. Under ADR base there are multiple ADR homes. Each ADR home is the root directory for all traces within particular instance.

ADR base/diag
        /rdbms
                /dbname
                            /alerts
                            /cdump
                            /incident
                            /trace


show parameter diag - displays the ADR base