ORA-00471 处理方法笔记
SA安装好系统--（版本sule 32bit)后通知我可以安装数据库了。忙活半天，安装好oracle 9204后，准备建表空间导入数据。因为数据量
公司新上架一台服务到机房，硬件是IBM X3850 X5,硬件配置算是好的，内存有128GB。SA安装好系统--（版本sule 32bit)后通知我可以安装数据库了。忙活半天，安装好Oracle 9204后，准备建表空间导入数据。因为数据量比较大，我打算建立一个10G的数据文件用来存储这写数据。打入创建表空间的命令后，没过多久数据库出现宕机现象。后来我又重新操作一遍还是故障依旧。以下是日志信息：
alert.log:
Errors in file /u01/oracle/admin/orcl/bdump/orcl_pmon_13918.trc:
ORA-00471: DBWR process terminated with error
Wed Aug 21 15:56:16 2013
PMON: terminating instance due to error 471
Instance terminated by PMON, pid = 13918
trace file:
*** 2013-08-21 15:56:16.296
*** SESSION ID:(1.1) 2013-08-21 15:56:16.277
error 471 detected in background process
ORA-00471: DBWR process terminated with error
/var/log/messages：
Aug 21 14:01:14 dzjg kernel: lowmem_reserve[]: 0 872 62301 62301
Aug 21 14:01:14 dzjg kernel: Node 0 Normal free:3704kB min:3744kB low:4680kB high:5616kB active:3096kB inactive:3092kB present:893200kB
…
…
Aug 21 14:01:14 dzjg kernel: Out of memory: kill process 12867 (oracle) score 414016 or a child
Aug 21 14:01:14 dzjg kernel: Killed process 12867 (oracle)
初步判断是系统内存不够，但是通过free -m查看系统有60G的内存。通过上网查阅相关文档对故障分析如下：
1.出现故障的原因：
在32位CPU下寻址范围是有限的，Linux内核定义了下面三个区域：
# DMA: 0x00000000 - 0x00999999 (0 - 16 MB)
# LowMem: 0x01000000 - 0x037999999 (16 - 896 MB) - size: 880MB
# HighMem: 0x038000000 - （由服务器硬件决定 ）
在 32位系统中，内存被分为 以上3 个区域，DMA zone，Normal zone（也叫做LowMem）和 HighMem zone其中 DMA zone主要用于 DMA 传输数据，位于低地址空间，其服务对象为各种驱动程序，其大小为 16MB，其中 LowMem (也叫做Normal zone)是 kernel 可以直接访问的地址空间，其大小为 880 MB，基本上所有的内核数据都在这个区域，同时如果内核要访问更高地址空间的内容，均需要通过 Normal zone映射过去才可以。地址空间大于 880 MB 的为 HIghMem zone.
截取的系统日志如下：
Aug 21 14:01:14 dzjg kernel: lowmem_reserve[]: 0 872 62301 62301
Aug 21 14:01:14 dzjg kernel: Node 0 Normal free:3704kB min:3744kB low:4680kB high:5616kB active:3096kB inactive:3092kB present:893200kB
…
…
Aug 21 14:01:14 dzjg kernel: Out of memory: kill process 12867 (oracle) score 414016 or a child
Aug 21 14:01:14 dzjg kernel: Killed process 12867 (oracle)
我们可以看到normal zone free 3704KB ，内核申请最小的内存3744KB，此时系统空闲的lowmem 3704KB，不能满足需求。该问题是low memory耗尽，因为内核使用low memory来跟踪所有的内存分配。当low memory耗尽，不管high memory剩多少，会触发oom-killer机制（out of memory killer）杀死进程，以保持系统的正常运行。根据一些文档描述，OOM-Killer 在 2.4 与 2.6 上表现是不一样的。2.4的版本中是把新进来(新申请内存)的进程杀掉。而 2.6上是杀掉占用内存最厉害的进程(这是很危险的，很容易导致系统应用瘫痪)。我们目前的系统内核版本为2.6，从而导致系统将数据库LGWR进程杀死.
相关阅读：
SPFILE 错误导致数据库无法启动(ORA-01565)
ORA-01172、ORA-01151错误处理
ORA-00600 [2662]错误解决
ORA-01078 和 LRM-00109 报错解决方法
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