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Need an explanation of Intimate Shared Memory

3 posts in Unix Last posting was on 2001-05-22 13:58:31.0Z
Michael Heaney Posted on 2001-05-17 14:45:51.0Z
Message-ID: <3B03E41F.C14D6978@tigr.org>
Date: Thu, 17 May 2001 10:45:51 -0400
From: Michael Heaney <mheaney@tigr.org>
Organization: The Institute for Genomic Research
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Can someone with a better knowledge of Solaris than me (which probably
includes just about everyone else this group) please educate me about the
concept and usage of Intimate Shared Memory?

I'm running 11.9.2 on a Solaris 2.6 machine with 4GB of memory, of which
3.6GB is dedicated to my Sybase server. But the Unix guy who initially
configured the machine created just a single 2GB swap partition. While
foraging around in deja.com for information about how a user's program
could exhaust swap space, I came across several references to ISM, which
indicated that if a program could copy its shared memory segments
completely into swap, then it could take advantage of ISM.

So I'm wondering: what, exactly, is ISM? And if I were to add another
2GB swap partition (thus allowing all 3.6GB of Sybase to be copied
into it), would I see any performance improvement?

Thanks in advance...




Michael Heaney
TIGR


Shashikant Bhandari Posted on 2001-05-17 18:33:57.0Z
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Date: Thu, 17 May 2001 14:33:57 -0400
From: Shashikant Bhandari <bhandari@sybase.com>
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Michael,

Intimate shared memory is specific feature of sun solaris. This feature
was developed so that when multiple processes (at OS level) tries to access
shared memory region, do not use multiple TLB (Transalation lookaside buffer)
at OS kernel level. This saves lot of kernel memory space. Typically, using
Oracle server (I do not know about latest version, but some time back this
was true), client conneciton would appear as a OS process, while for Sybase,
client conneciton will not be seen as OS process, but it will only use socket
(plus few more resources).

With this said, another advantage I think is that if there is engough
memory available on the machine, typically sun solaris does not swap out
process memory marked as ISM. Swapping in solaris is done in three phases,
reserved, allocated and used. Locking the shared memory have an advantage of
increasing the performance. Of course, if there are lot's of processes on the
machine and if new processes starve for memory, it is a potential that ISM
would get swapped. If some one are looking for performance, they should make
sure that in the environment, never database memory get swapped out.

Personally I would recommend 1X physical memory as swap space. Adding
more swap may not improve performance, however it may help in case there is
some starvation of physical memory.

If some one has access to sunsolve web site, then they can check more
detail about this, also there was very good article about this on sunworld
few years back.

HTH

Regards,

Michael Heaney wrote:

> Can someone with a better knowledge of Solaris than me (which probably
> includes just about everyone else this group) please educate me about the
> concept and usage of Intimate Shared Memory?
>
> I'm running 11.9.2 on a Solaris 2.6 machine with 4GB of memory, of which
> 3.6GB is dedicated to my Sybase server. But the Unix guy who initially
> configured the machine created just a single 2GB swap partition. While
> foraging around in deja.com for information about how a user's program
> could exhaust swap space, I came across several references to ISM, which
> indicated that if a program could copy its shared memory segments
> completely into swap, then it could take advantage of ISM.
>
> So I'm wondering: what, exactly, is ISM? And if I were to add another
> 2GB swap partition (thus allowing all 3.6GB of Sybase to be copied
> into it), would I see any performance improvement?
>
> Thanks in advance...
>
> Michael Heaney
> TIGR


Michael Heaney Posted on 2001-05-22 13:58:31.0Z
Message-ID: <3B0A7087.3BCEE2E6@tigr.org>
Date: Tue, 22 May 2001 09:58:31 -0400
From: Michael Heaney <mheaney@tigr.org>
Organization: The Institute for Genomic Research
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Article PK: 1092521

Thanks very much - I reconfigured my swap partitions to be 1.5x RAM, and
now my server is using IMS.


Michael Heaney
TIGR

Shashikant Bhandari wrote:
>
> Michael,
>
> Intimate shared memory is specific feature of sun solaris. This feature
> was developed so that when multiple processes (at OS level) tries to access
> shared memory region, do not use multiple TLB (Transalation lookaside buffer)
> at OS kernel level. This saves lot of kernel memory space. Typically, using
> Oracle server (I do not know about latest version, but some time back this
> was true), client conneciton would appear as a OS process, while for Sybase,
> client conneciton will not be seen as OS process, but it will only use socket
> (plus few more resources).
>
> With this said, another advantage I think is that if there is engough
> memory available on the machine, typically sun solaris does not swap out
> process memory marked as ISM. Swapping in solaris is done in three phases,
> reserved, allocated and used. Locking the shared memory have an advantage of
> increasing the performance. Of course, if there are lot's of processes on the
> machine and if new processes starve for memory, it is a potential that ISM
> would get swapped. If some one are looking for performance, they should make
> sure that in the environment, never database memory get swapped out.
>
> Personally I would recommend 1X physical memory as swap space. Adding
> more swap may not improve performance, however it may help in case there is
> some starvation of physical memory.
>
> If some one has access to sunsolve web site, then they can check more
> detail about this, also there was very good article about this on sunworld
> few years back.
>
> HTH