这篇文章给大家介绍ORACLE占用大量系统CPU致使系统宕机该怎么办，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。
Oracle数据库经常会遇到CPU利用率很高的情况，这种时候大都是数据库中存在着严重性能低下的SQL语句，这种SQL语句大大的消耗了CPU资源，导致整个系统性能低下。当然，引起严重性能低下的SQL语句的原因是多方面的，具体的原因要具体的来分析，下面通过一个实际的案例来说明如何来诊断和解决CPU利用率高的这类问题。
操作系统：Linux7.0
数据库：Oracle11.2.0.4
问题描述：现场工程师汇报数据库非常慢，几乎所有应用操作均无法正常进行。不久后，系统断开连接，宕机。
首先重启系统后，启动数据库。执行top发现CPU资源几乎消耗殆尽，存在很多占用CPU很高的进程，而内存和I/O都不高，具体如下：
last pid: 26136; load averages: 8.89, 8.91, 8.12
216 processes: 204 sleeping, 8 running, 4 on cpu
CPU states: 0.6% idle, 97.3% user, 1.8% kernel, 0.2% iowait, 0.0% swap
Memory: 8192M real, 1166M free, 14M swap in use, 8179M swap free
PID USERNAME THR PRI NICE SIZE RES STATE TIME CPU COMMAND
25725 oracle 1 50 0 4550M 4508M cpu2 12:23 11.23% oracle
25774 oracle 1 41 0 4550M 4508M run 14:25 10.66% oracle
26016 oracle 1 31 0 4550M 4508M run 5:41 10.37% oracle
26010 oracle 1 41 0 4550M 4508M run 4:40 9.81% oracle
26014 oracle 1 51 0 4550M 4506M cpu6 4:19 9.76% oracle
25873 oracle 1 41 0 4550M 4508M run 12:10 9.45% oracle
25723 oracle 1 50 0 4550M 4508M run 15:09 9.40% oracle
26121 oracle 1 41 0 4550M 4506M cpu0 1:13 9.28% oracle
25745 oracle 1 41 0 4551M 4512M run 9:33 9.28% oracle
26136 oracle 1 41 0 4550M 4506M run 0:06 5.61% oracle
409 root 15 59 0 7168K 7008K sleep 173.1H 0.52% picld
25653 oracle 1 59 0 4550M 4508M sleep 1:01 0.46% oracle
25565 oracle 1 59 0 4550M 4508M sleep 0:07 0.24% oracle
25703 oracle 1 59 0 4550M 4506M sleep 0:08 0.13% oracle
25701 oracle 1 59 0 4550M 4509M sleep 0:23 0.10% oracle
于是先查看数据库的告警日志ALERT文件，并没有发现有什么错误存在，日志显示数据库运行正常，排除数据库本身存在问题。
然后查看这些占用CPU资源很高的Oracle进程究竟是在做什么操作，使用如下SQL语句：
select sql_text,spid,v$session.program,process from
v$sqlarea,v$session,v$process
where v$sqlarea.address=v$session.sql_address
and v$sqlarea.hash_value=v$session.sql_hash_value
and v$session.paddr=v$process.addr
and v$process.spid in (PID);
用top中占用CPU很高的进程的PID替换脚本中的PID,得到相应的Oracle进程所执行的SQL语句，发现占用CPU资源很高的进程都是执行同一个SQL语句：
select username "username", to_char(timestamp,'DD-MON-YYYY HH24:MI:SS') "time_stamp", action_name "statement", os_username "os_username", userhost "userhost", returncode||decode(returncode,'1004','-Wrong Connection','1005','-NULL Password','1017','-Wrong Password','1045','-Insufficient Priviledge','0','-Login Accepted','--') "returncode" from sys.dba_audit_session where (sysdate - timestamp)*24 < 1 and returncode <> 0 order by timestamp;
基本上可以肯定是这个SQL引起了系统CPU资源大量被占用，那究竟是什么原因造成这个SQL这么大量占用CPU资源呢，从上面的SQL语句中我们可以看到sys.dba_audit_session这张表，由此可以确定是由于审计的原因导致数据库占用大量CPU。
查看数据库审计信息：
SQL> show parameter audit
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
audit_file_dest string /u01/app/oracle/admin/orcl/adump
audit_sys_operations boolean FALSE
audit_syslog_level string
audit_trail string DB
可以看到数据库审计为开启状态，并且将audited record的存放在数据库里（sys.aud$）中。
问题处理方法：
如果审计不是必须的，可以关掉审计功能；
SQL> alter system set audit_trail=none scope=spfile;
SQL>showdown immediate;
SQL>startup
删除已有的审计信息
可以直接truncate表aud$,
或者采取dbms_audit_mgmt来清除。
或者将aud$表移到另外一个表空间下，以减少system表空间的压力和被撑爆的风险。
附：11g中有关audit_trail参数的设置说明：
AUDIT_TRAIL
| Property | Description |
|---|---|
| Parameter type | String |
| Syntax | AUDIT_TRAIL = { none | os | db [, extended] | xml [, extended] } |
| Default value | none |
| Modifiable | No |
| Basic | No |
AUDIT_TRAIL enables or disables database auditing.
Values:
none
Disables standard auditing. This value is the default if the AUDIT_TRAIL parameter was not set in the initialization parameter file or if you created the database using a method other than Database Configuration Assistant. If you created the database using Database Configuration Assistant, then the default is db.
os
Directs all audit records to an operating system file. Oracle recommends that you use the os setting, particularly if you are using an ultra-secure database configuration.
db
Directs audit records to the database audit trail (the SYS.AUD$ table), except for records that are always written to the operating system audit trail. Use this setting for a general database for manageability.
If the database was started in read-only mode with AUDIT_TRAIL set to db, then Oracle Database internally sets AUDIT_TRAIL to os. Check the alert log for details.
db, extended
Performs all actions of AUDIT_TRAIL=db, and also populates the SQL bind and SQL text CLOB-type columns of the SYS.AUD$ table, when available. These two columns are populated only when this parameter is specified.
If the database was started in read-only mode with AUDIT_TRAIL set to db, extended, then Oracle Database internally sets AUDIT_TRAIL to os. Check the alert log for details.
xml
Writes to the operating system audit record file in XML format. Records all elements of the AuditRecord node except Sql_Text and Sql_Bind to the operating system XML audit file.
xml, extended
Performs all actions of AUDIT_TRAIL=xml, and populates the SQL bind and SQL text CLOB-type columns of the SYS.AUD$table, wherever possible. These columns are populated only when this parameter is specified.
You can use the SQL AUDIT statement to set auditing options regardless of the setting of this parameter.
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