【翻译自mos文章】当NFS server 宕机后，Oracle 数据库 冻结并且alert 文件里没有任何错误

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当NFS server 宕机后，Oracle 数据库 冻结并且alert 文件里没有任何错误

翻译自mos文章：When NFS Server Is Down, Oracle Server Freezes With No Errors In Alert Log File (文档 ID 1316251.1)

适用于：
Oracle Server - Enterprise Edition - Version: 10.2.0.4 and later   [Release: 10.2 and later ]
IBM AIX on POWER Systems (64-bit)
症状：
AIX上的Oracle instance 有一个NFS 挂载点，该挂载点基于backup 的目的。 该挂载点mount时的选项如下：

bg,hard,intr,rsize=32768,wsize=32768,sec=sys,noac,rw

当NFS Server 宕机时，Ooracle RDMBS 冻结，并且alert 日志中没有任何错误。当NFS Sserver 恢复后，database 也正常工作，没有任何问题。

改变：
环境没有改变，仅仅是丢失了NAS connectivity（to NFS Server）,因此远程的目录不可访问。
原因：

从上传的sqlplus 和df 的 tusss跟踪来看，我们可以看到statx 命令在 /backup处挂起。

462940: statx("./../../../../backup", 0x0FFFFFFFFFFF5980, 176, 021) (sleeping...)
561338: kread(14, " ÿ ÿ J ø\0\0\0\0\0\0\010".., 64) Err#82 ERESTART
561338: Received signal #2, SIGINT [caught]
561338: sigprocmask(0, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: sigprocmask(1, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: ksetcontext_sigreturn(0x0FFFFFFFFFFF37A0, 0x0000000000000000, 0x00000001100F04F0,
0x800000000000D032, 0x3000000000000000, 0x0000000000000360, 0x0000000000000000, 0x0000000000000000)
561338: kread(14, " ÿ ÿ J ø\0\0\0\0\0\0\010".., 64) Err#82 ERESTART
561338: Received signal #2, SIGINT [caught]
561338: sigprocmask(0, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: sigprocmask(1, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: ksetcontext_sigreturn(0x0FFFFFFFFFFF37A0, 0x0000000000000000, 0x00000001100F04F0,
0x800000000000D032, 0x3000000000000000, 0x0000000000000320, 0x0000000000000000, 0x0000000000000000)
561338: kread(14, " ÿ ÿ J ø\0\0\0\0\0\0\010".., 64) Err#82 ERESTART
561338: Received signal #2, SIGINT [caught]
561338: sigprocmask(0, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: sigprocmask(1, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: ksetcontext_sigreturn(0x0FFFFFFFFFFF37A0, 0x0000000000000000, 0x00000001100F04F0,
0x800000000000D032, 0x3000000000000000, 0x0000000000000310, 0x0000000000000000, 0x0000000000000000)
561338: kread(14, " ÿ ÿ J ø\0\0\0\0\0\0\010".., 64) Err#82 ERESTART
561338: Received signal #2, SIGINT [caught]
561338: sigprocmask(0, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: sigprocmask(1, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: ksetcontext_sigreturn(0x0FFFFFFFFFFF37A0, 0x0000000000000000, 0x00000001100F04F0,
0x800000000000D032, 0x3000000000000000, 0x0000000000000310, 0x0000000000000000, 0x0000000000000000)
561338: kread(14, " ÿ ÿ J ø\0\0\0\0\0\0\010".., 64) Err#82 ERESTART
561338: Received signal #2, SIGINT [caught]
561338: sigprocmask(0, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: sigprocmask(1, 0x0FFFFFFFFFFF3620, 0x0000000000000000) = 0
561338: ksetcontext_sigreturn(0x0FFFFFFFFFFF37A0, 0x0000000000000000, 0x00000001100F04F0,
0x800000000000D032, 0x3000000000000000, 0x0000000000000320, 0x0000000000000000, 0x0000000000000000)
561338: kread(14, " ÿ ÿ J ø\0\0\0\0\0\0\010".., 64) (sleeping...)
462940: statx("./../../../../backup", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../usr", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../lib", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../audit", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../dev", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../etc", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../u", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../lpp", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../mnt", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../proc", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../sbin", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../bin", 0x0FFFFFFFFFFF5980, 176, 021) = 0
462940: statx("./../../../../oracle", 0x0FFFFFFFFFFF5980, 176, 021) = 0

问题在下面的地方：

statx("./../../../../backup", 0x0FFFFFFFFFFF5980, 176, 021) (sleeping...)

Oracle 程序（代码）调用一个Unix 系统调用（system call）， ‘getcwd‘来得到当前的工作目录。在这之后，所有的控制权归还给操作系统。
从我们所看到的， 函数‘getcwd‘ 调用‘getwd‘，而‘getwd‘会依次调用‘statx‘。一旦‘statx‘被执行，它就按照 下面的顺序 通过执行‘statx‘ 开始处理directory entries

./
./..
./../..
./../../.. (this goes on until the root directory is reached)

一旦 root 目录（/）被到达，那么对于目录中的每个entry，‘lstat‘会调用 ‘statx‘。Oracle 完全不控制这个处理过程，因此为了防止此情况发生，我们做不了任何事情（这完全是os级别的事情）

解决方法：
从一个类似问题中，IBM 已经建议下面的 action plan  以避免这个问题。来自IBM的回答是：

Here's a solution to avoid the problem described by Oracle: 
DO NOT have the NFS mounts directly under /, but put them one level lower. Then, we can use symbolic links to them.

NFS mount point on node  /nfs/backup (/nfs is a directory we'll create, it can have any name) and create a softlink /backup -> /nfs/backup.
 
$ ln -s /nfs/backup /backup

This will avoid the statx problem without having to make changes in the setup (because /backup is still there).

Additionally you can ask IBM about APAR # IZ85027, IZ85029, IZ85032, IZ86102, IZ87374, IZ90533.

Check with IBM which one applies to your configuration.

【翻译自mos文章】当NFS server 宕机后，Oracle 数据库 冻结并且alert 文件里没有任何错误

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原文地址：http://blog.csdn.net/msdnchina/article/details/43866323