ORACLE告警日志文件（ alert log file）存储信息

存放位置：由初始化参数background_dump_dest决定（默认：$ORACLE_HOME/rdbms/log/alert_SID.log） 
内容包括：系统内部错误(Ora-600)；数据块损坏(Ora-1578,Ora-1498)；影响数据库结构，初始化参数等的操作记录；Instance启动时记录所有非默认值的初始化参数； 

（如果初始化参数log_checkpoints_to_alert设置为true，则还会记录checkpoit的开始和结束时间，未完成的checkpoint，归档日志需要的时间，实例恢复的开始和结束时间等）

官方说明：

The alert log is a chronological log of messages and errors, and includes the following items: 

All internal errors (ORA-00600), block corruption errors (ORA-01578), and deadlock errors (ORA-00060) that occur 

Administrative operations, such as CREATE, ALTER, and DROP statements and STARTUP, SHUTDOWN, and ARCHIVELOG statements 

Messages and errors relating to the functions of shared server and dispatcher processes 

Errors occurring during the automatic refresh of a materialized view 

The values of all initialization parameters that had nondefault values at the time the database and instance start 

Oracle Database uses the alert log to record these operations as an alternative to displaying the information on an operator's console (although some systems also display information on the console). If an operation is successful, a "completed" message is written in the alert log, along with a timestamp.