linux 共享内存段研究
无论是在unix或者是linux都有命令查看主机共享内存段的使用情况，以下研究来自linux平台。
一、查看Oracle用户共享内存段使用情况
------SharedMemorySegments--------
keyshmidownerpermsbytesnattchstatus
0x00000000917504oracle6001966082dest
0x00000000950273oracle6001966082dest
0x00000000983042oracle6001966082dest
0x000000001015811oracle6001966082dest
0x000000001081349oracle6001966082dest
0x000000001179656oracle6001966082dest
0x4cd26024524300oracle64056204492855
0x000000001900559oracle600122882dest
0x000005061802260oracle666163840
0x000000001835029oracle6001966082dest
------SemaphoreArrays--------
keysemidownerpermsnsems
0xc7ef5bb098304oracle640152
0xc7ef5bb1131073oracle640152
0xc7ef5bb2163842oracle640152
------MessageQueues--------
keymsqidownerpermsused-bytesmessages
简单说明：
shmid：表示共享内存段id
owner：表示共享内存段属于哪个用户，需要注意的是默认情况下600表示除root用户外不允许其他用户查看
bytes：表示共享内存段大小
nattch：表示连接到共享内存段的进程数
status：表示共享内存段的状态，dest表示该内存段被标记为destroyed状态。
二、查看共享内存段进程连接信息
1、指定shmid，查看进程连接信息
查看shmid为524300的具体信息，可用如下命令
SharedmemorySegmentshmid=524300
uid=505gid=505cuid=505cgid=505
mode=0640access_perms=0640
bytes=562044928lpid=15216cpid=16790nattch=55
att_time=WedDec913:44:452009
det_time=WedDec913:44:452009
change_time=FriNov2715:58:442009
2、查看所有共享内存段，进程连接信息
------SharedMemoryCreator/Last-op--------
shmidownercpidlpid
917504oracle3043830967
950273oracle304401286
983042oracle3123430967
1015811oracle3123630967
1081349oracle317081275
1179656oracle3166130967
524300oracle1679015410
1900559oracle131529959
1802260oracle12860
1835029oracle131529959
简单说明：
cpid表示创建共享内存段进程的id
lpid表示上一次访问该共享内存的进程id
三、查看Oracle使用共享内存段使用情况
1、使用Oracle小工具查看共享内存段使用情况
Oracle软件装好之后自带一个工具（sysresv），可以清晰的看到每个实例的内存使用情况，默认安装在$ORACLE_HOME/bin目录下，以下是sysresv的输出情况
IPCResourcesforORACLE_SID"xe":
SharedMemory:
IDKEY
5243000x4cd26024
Semaphores:
IDKEY
983040xc7ef5bb0
1310730xc7ef5bb1
1638420xc7ef5bb2
OracleInstancealiveforsid"xe"
可以看到SID为xe的实例使用了shmid为524300的共享内存段
2、使用oradebug命令行查看共享内存段使用情况
1）连接到需要查看的数据库中
2）取得连接的ospid
oracle1649716496013:57?00:00:00oraclexe(DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
3）根据ospid利用oradebug产生跟踪文件
SQL>oradebugsetospid16497
Statementprocessed.
SQL>oradebugipc
Informationwrittentotracefile.
SQL>oradebugtracefile_name
/var/oracle/admin/xe/udump/xe_ora_16497.trc
4）打开跟踪文件可以看到该实例共享内存使用情况，其中shmid为524300
/var/oracle/admin/xe/udump/xe_ora_16497.trc
OracleDatabase10gEnterpriseEditionRelease10.2.0.1.0-64bitProduction
WiththePartitioning,OLAPandDataMiningoptions
ORACLE_HOME=/var/oracle/product/10.2.0/db_1
Systemname:Linux
Nodename:capaa
Release:2.6.18-53.el5xen
Version:#1SMPMonNov1202:46:57EST2007
Machine:x86_64
Instancename:xe
Redothreadmountedbythisinstance:1
Oracleprocessnumber:55
Unixprocesspid:16497,image:oracle@capaa(TNSV1-V3)
***2009-12-0914:02:27.230
***SERVICENAME:(SYS$USERS)2009-12-0914:02:27.171
***SESSIONID:(262.2351)2009-12-0914:02:27.171
Dumpofunix-genericskgmcontext
areaflags000000a7
realmflags0000000f
mapsize00001000
protectsize00001000
lcmsize00001000
seglen00001000
largestsize0000001000000000
smallestsize0000000000400000
stacklimit0x7fff2207dac0
stackdir-1
mode640
magicacc01ade
Handle:0x185252d0`/var/oracle/product/10.2.0/db_1xe'
Dumpofunix-genericrealmhandle`/var/oracle/product/10.2.0/db_1xe',flags=00000000
Area#0`FixedSize'containingSubareas0-0
Totalsize00000000001edba8MinimumSubareasize00000000
AreaSubareaShmidStableAddrActualAddr
005243000x000000600000000x00000060000000
SubareasizeSegmentsize
00000000001ee0000000000021802000
Area#1`VariableSize'containingSubareas2-2
Totalsize0000000021000000MinimumSubareasize00400000
AreaSubareaShmidStableAddrActualAddr
125243000x000000608000000x00000060800000
SubareasizeSegmentsize
00000000210000000000000021802000
Area#2`RedoBuffers'containingSubareas1-1
Totalsize0000000000612000MinimumSubareasize00000000
AreaSubareaShmidStableAddrActualAddr
215243000x000000601ee0000x000000601ee000
SubareasizeSegmentsize
00000000006120000000000021802000
Area#3`skgmoverhead'containingSubareas3-3
Totalsize0000000000002000MinimumSubareasize00000000
AreaSubareaShmidStableAddrActualAddr
335243000x000000818000000x00000081800000
SubareasizeSegmentsize
00000000000020000000000021802000
DumpofSolaris-specificskgmcontext
sharedmmu00000000
shareddec0
usedregion0:start0000000040000000length000000007fff80000000
Maximumprocesses:=300
Numberofsemaphoresperset:=152
Semaphoreskeyoverheadperset:=4
UserSemaphoresperset:=148
Numberofsemaphoresets:=3
Semaphoreidentifiers:=3
SemaphoreList=
98304
--------------systemsemaphoreinformation-------------
------SharedMemorySegments--------
keyshmidownerpermsbytesnattchstatus
0x00000000917504oracle6001966082dest
0x00000000950273oracle6001966082dest
0x00000000983042oracle6001966082dest
0x000000001015811oracle6001966082dest
0x000000001081349oracle6001966082dest
0x000000001179656oracle6001966082dest
0x4cd26024524300oracle64056204492855
0x000000001900559oracle600122882dest
0x000005061802260oracle666163840
0x000000001835029oracle6001966082dest
------SemaphoreArrays--------
keysemidownerpermsnsems
0xc7ef5bb098304oracle640152
0xc7ef5bb1131073oracle640152
0xc7ef5bb2163842oracle640152
------MessageQueues--------
keymsqidownerpermsused-bytesmessages
四、进一步研究
通过以上命令可以查看创建Oracle实例的初始进程
[oracle@capaa~]$ipcs-mi524300
SharedmemorySegmentshmid=524300
uid=505gid=505cuid=505cgid=505
mode=0640access_perms=0640
bytes=562044928lpid=19796cpid=16790nattch=54
att_time=WedDec914:10:262009
det_time=WedDec914:10:352009
change_time=FriNov2715:58:442009
通过cpid=16790可以知道pid为16790启动了Oracle实例，该进程只负责启动Oracle实例，启动完成后通过“自杀”结束进程，可以从两方面得到验证
1）启动日志
PSP0startedwithpid=3,OSid=30347
MMANstartedwithpid=4,OSid=30349
DBW0startedwithpid=5,OSid=30351
LGWRstartedwithpid=6,OSid=30353
CKPTstartedwithpid=7,OSid=30355
SMONstartedwithpid=8,OSid=30357
RECOstartedwithpid=9,OSid=30359
CJQ0startedwithpid=10,OSid=30361
MMONstartedwithpid=11,OSid=30363
2）从v$process表中查相关信息
ADDRPROGRAM
----------------------------------------------------------------
00000000817DA930PSEUDO
PSEUDO表示该进程已被killed