Topic: Oracle on Unix/Linux >> shared memory & shemaphore in Linux/Unix
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| Title: shared memory & shemaphore in Linux/Unix |
| micky |
Posted: Apr 21, 2008 02:22:43 PM |
Total Post: 2
Joined: Apr, 2008
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Hi,
Can any one explain me that why we configure shared memory and Semaphore kernel parameter in Linux/ Unix platform and why not in windows.
what happen if we did not configure it. Is it possible to install oracle on these flavor's. |
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 Murtuja |
| Posted: Apr 22, 2008 12:58:39 AM |  |
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Total Post: 814
Joined: Jan, 2006
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Please do not post the same thread in more than one forum. Picking the most relevant forum and posting it once there makes it easier for other members to help you and keeps the discussion all in one place.
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| Chandrasekharan |
| Posted: May 21, 2008 11:45:31 AM | |
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Total Post: 7
Joined: Mar, 2007
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Shared Memory,Semaphore and Message Queue are three kernel terms used in
Unix platforms very frequently with Oracle DB Installations.
If a Unix node is going to host more than one instance at a time,these
parameters have to be meticulously adjusted.
Every Unix OS have its on default values for various kernel parameters,and
it is sufficient in single instance case,most of the time.Among the above
three,semaphore and Message queue values will be derrived normally from PROCESS parameter value in INIT.ORA as a soft limit.But if the number of
users and process are large,we may have to adjust the hard limit also and
that hard limit we are setting through Kernel Parameters.
With respect to Shared memory a longer discussion is required.
SHMALL - Total shared memory availble
SHMMAX - Max Memory per segment
SHMMNI - Max number of segment
Suppose MAX = 200M and MNI = 10 then total will be 2000M -- I
and again,
suppose MAX = 50M and MNI = 40 Then total will be 2000M -- II
If an instance wants to have 1050M,then it have to use 6 segment in case I
and wasting 150M, where as in case II ,the allocation can be more refined
and will be using 21 segments and allocate exactly 1050M. So memory is
allocated more efficiently without wastage.When more than one instance
like that of ASM and 10G RAC of ORACLE ,to be hosted concurrently,memory
segmentation should be very efficient,as memory modules are costly.
I think this clarifies the question.
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