shmmax

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我是靠谱客的博主丰富身影，最近开发中收集的这篇文章主要介绍shmmax，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

shmmax内核参数定义是系统允许的单个共享内存段的最大值
现在模拟设置shmmax很小：
[root@localhost kernel]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.5 (Tikanga)

SQL> select * from v$version where rownum=1;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production

[root@localhost ~]# cd /proc/sys/kernel | echo 1000 > shmmax => 注意：该种修改会在os重启后失效

[oracle@localhost ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.1.0 Production on 星期日 5月 10 23:27:36 2015

Copyright (c) 1982, 2009, Oracle. All rights reserved.

ERROR:
ORA-12547: TNS: 丢失连接

请输入用户名:

告警日志：
......
......
Sun May 10 23:27:42 2015
Process J000 died, see its trace file
kkjcre1p: unable to spawn jobq slave process
Errors in file /u01/app/oracle/diag/rdbms/orcl3939/orcl3939/trace/orcl3939_cjq0_10511.trc:
Process J000 died, see its trace file
kkjcre1p: unable to spawn jobq slave process
Errors in file /u01/app/oracle/diag/rdbms/orcl3939/orcl3939/trace/orcl3939_cjq0_10511.trc:

/u01/app/oracle/diag/rdbms/orcl3939/orcl3939/trace/orcl3939_cjq0_10511.trc:

Trace file /u01/app/oracle/diag/rdbms/orcl3939/orcl3939/trace/orcl3939_cjq0_10511.trc
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
ORACLE_HOME = /u01/app/oracle/product/11.2.0/dbhome_1
System name: Linux
Node name: localhost.localdomain
Release: 2.6.18-194.el5
Version: #1 SMP Mon Mar 29 20:06:41 EDT 2010
Machine: i686
Instance name: orcl3939
Redo thread mounted by this instance: 1
Oracle process number: 25
Unix process pid: 10511, image: oracle@localhost.localdomain (CJQ0)

*** 2015-05-10 23:08:21.485
*** SESSION ID:(133.9) 2015-05-10 23:08:21.485
*** CLIENT ID:() 2015-05-10 23:08:21.485
*** SERVICE NAME:(SYS$BACKGROUND) 2015-05-10 23:08:21.485
*** MODULE NAME:() 2015-05-10 23:08:21.485
*** ACTION NAME:() 2015-05-10 23:08:21.485

Setting Resource Manager plan SCHEDULER[0x3009]:DEFAULT_MAINTENANCE_PLAN via scheduler window
Setting Resource Manager plan DEFAULT_MAINTENANCE_PLAN via parameter

*** 2015-05-10 23:27:42.805
Process J000 is dead (pid=11060 req_ver=3 cur_ver=3 state=KSOSP_SPAWNED).

*** 2015-05-10 23:27:43.876
Process J000 is dead (pid=11063 req_ver=16 cur_ver=16 state=KSOSP_SPAWNED).

*** 2015-05-10 23:28:43.621
Process J000 is dead (pid=11106 req_ver=5 cur_ver=5 state=KSOSP_SPAWNED).

*** 2015-05-10 23:28:44.743
Process J000 is dead (pid=11109 req_ver=17 cur_ver=17 state=KSOSP_SPAWNED).

*** 2015-05-10 23:34:43.874
Process J000 is dead (pid=11244 req_ver=6 cur_ver=6 state=KSOSP_SPAWNED).

*** 2015-05-10 23:34:44.888
Process J000 is dead (pid=11247 req_ver=18 cur_ver=18 state=KSOSP_SPAWNED).

*** 2015-05-10 23:35:42.550
Process J000 is dead (pid=11280 req_ver=7 cur_ver=7 state=KSOSP_SPAWNED).

*** 2015-05-10 23:35:43.565
Process J000 is dead (pid=11285 req_ver=19 cur_ver=19 state=KSOSP_SPAWNED).

[oracle@localhost ~]$ ipcs -a

------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00000000 3276801 oracle 600 393216 2 dest
0x00000000 3309571 oracle 600 393216 2 dest
0x00000000 3342340 oracle 600 393216 2 dest
0x00000000 3375109 oracle 600 393216 2 dest
0x00000000 3407878 oracle 600 393216 2 dest
0x00000000 3440647 oracle 600 393216 2 dest
0x00000000 3473416 oracle 600 393216 2 dest
0x00000000 3506185 oracle 600 393216 2 dest
0x00000000 3538954 oracle 600 393216 2 dest
0x00000000 3571723 oracle 600 393216 2 dest
0x05a35eec 4194316 oracle 660 4096 0
0x038880a0 3735567 oracle 755 1079228 0

------ Semaphore Arrays --------
key semid owner perms nsems
0xed251740 622592 oracle 660 154

------ Message Queues --------
key msqid owner perms used-bytes messages

SQL> select * from v$sgainfo;

NAME BYTES RES
-------------------------------- ---------- ---
Fixed SGA Size 1336960 No
Redo Buffers 6094848 No
Buffer Cache Size 79691776 Yes
Shared Pool Size 176160768 Yes
Large Pool Size 4194304 Yes
Java Pool Size 4194304 Yes
Streams Pool Size 4194304 Yes
Shared IO Pool Size 0 Yes
Granule Size 4194304 No
Maximum SGA Size 422670336 No
Startup overhead in Shared Pool 58720256 No

NAME BYTES RES
-------------------------------- ---------- ---
Free SGA Memory Available 146800640

如果shmmax的大小小于SGA设置，那么sga任然可以创建成功，但是会被分配多个共享内存段，但是这个shmmax的大小要有底线，
否则 OS资源被耗尽，Process J000 is dead
通常建议shmmax设置大些，把sga限制在一个共享内存段中。

官方文档：
Memory Resources

The resources provided by the UNIX default kernels are often inadequate for a medium or large instance of Oracle Database. The maximum size of a shared memory segment (SHMMAX) and maximum number of semaphores available (SEMMNS) may be too low for Oracle Database recommendations.
由UNIX默认内核提供的资源往往是不足的中型或大型的数据库实例。最大的共享内存段的大小（SHMMAX）和信号量可用的最大数目（SEMMNS）可能太低对Oracle数据库的建议。

On Windows, fewer resources are needed for interprocess communication (IPC), because the Oracle Database relational database management system is thread-based and not process-based. These resources, including shared memory and semaphores, are not adjustable by the user.

在Windows中，更少的资源用于进程间通信（IPC）所需要的，因为Oracle数据库的关系型数据库管理系统是基于线程的而不是进程。这些资源，包括共享内存和信号量，都是用户不可修改的。

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转载于:http://blog.itpub.net/29876893/viewspace-1647661/