一．首先介绍2个新名词
Automatic Diagnostic Repository (ADR)—
一个存放数据库诊断日志、跟踪文件的目录，称作ADR base，对应初始化参数DIAGNOSTIC_DEST，
如果设置了ORACLE_BASE环境变量，DIAGNOSTIC_DEST等于ORACLE_BASE，
如果没有设置ORACLE_BASE，则等与ORACLE_HOME/log。

SQL> show parameter diag
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
diagnostic_dest string /oracle/app/oracle
......
ADRCI Command-Line Utility 命令行工具
使用该工具查看日志，跟踪信息，查看健康报告。

[oracle@ora1 ~]$ adrci
ADRCI: Release 11.2.0.1.0 - Production on Sat Jul 10 18:47:33 2010
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
ADR base = "/oracle/app/oracle"
adrci> ?
DIA-48415: Syntax error found in string [?
] at column [2]
adrci> help
HELP [topic]
Available Topics:
CREATE REPORT
ECHO
EXIT
HELP
HOST
IPS
PURGE
RUN
SET BASE
SET BROWSER
SET CONTROL
SET ECHO
SET EDITOR
SET HOMES | HOME | HOMEPATH
SET TERMOUT
SHOW ALERT
SHOW BASE
SHOW CONTROL
SHOW HM_RUN
SHOW HOMES | HOME | HOMEPATH
SHOW INCDIR
SHOW INCIDENT
SHOW PROBLEM
SHOW REPORT
SHOW TRACEFILE
SPOOL
There are other commands intended to be used directly by Oracle, type
"HELP EXTENDED" to see the list

二．一个比较大的变化：aelrt xml file
在oracle 11g中，alert文件的信息是以xml的文件格式存在的，另外提供了普通文本格式的alert文件。
这两份log文件的位置分别是V$DIAG_INFO中的Diag Alert 和Diag Trace 对应的目录。
代码:

alert_ora11g.log文件存放：
/oracle/app/oracle/diag/rdbms/ora11g/ora11g/trace/alert_ora11g.log
/oracle/app/oracle/diag/rdbms/ora11g/ora11g/alert/log.xml
SQL> col NAME format a30
SQL> col VALUE format a80
SQL> select * from v$diag_info; INST_ID NAME VALUE
---------- ------------------------------ --------------------------------------------------------------------------------
1 Diag Enabled TRUE
1 ADR Base /oracle/app/oracle
1 ADR Home /oracle/app/oracle/diag/rdbms/ora11g/ora11g
1 Diag Trace /oracle/app/oracle/diag/rdbms/ora11g/ora11g/trace
1 Diag Alert /oracle/app/oracle/diag/rdbms/ora11g/ora11g/alert
1 Diag Incident /oracle/app/oracle/diag/rdbms/ora11g/ora11g/incident
1 Diag Cdump /oracle/app/oracle/diag/rdbms/ora11g/ora11g/cdump
1 Health Monitor /oracle/app/oracle/diag/rdbms/ora11g/ora11g/hm
1 Default Trace File /oracle/app/oracle/diag/rdbms/ora11g/ora11g/trace/ora11g_ora_4991.trc
1 Active Problem Count 0
1 Active Incident Count 0
11 rows selected.

Alert文件记录了：关键错误（Critical errors (incidents) ），数据库管理操作，包括启动关闭数据库，创建、删除表空间，
物化视图刷新错误等信息，另外我做试验的时候还发现还包括有一般的ddl操作，

三．查看alert文件的方法：
1.使用Enterprise Manager，进入Oracle database home page，在Related Links点击Alert Log Contents.
见图：
2.使用vi等文本编辑alert_SID.log （text-only alert log, without the XML tags）
3.使用工具adrci：
SQL> host
[oracle@ora1 pfile]$ which adrci
/oracle/app/oracle/product/11.2.0/dbhome_1/bin/adrci
[oracle@ractest ~]$ which adrci
/home/oracle/11g/bin/adrci
[oracle@ractest ~]$ adrci
ADRCI: Release 11.1.0.4.0 - Beta on Tue Jul 3 09:02:14 200
Copyright (c) 1982, 2006, Oracle. All rights reserved.
ADR base = "/home/oracle"
adrci>>help show alert
Usage: SHOW ALERT [-p ] [-tail [num]] [-v]
[-file ]
…………
Examples:
show alert
show alert -p "message_text like '%incident%'"
show alert -tail 20
adrci>>show alert -tail 10
ADR Home = /home/oracle/diag/rdbms/orcl/orcl: