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Cache Memory Size

2 posts in General Discussion Last posting was on 2010-08-11 14:09:32.0Z
SJ Posted on 2010-08-10 21:21:58.0Z
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Subject: Cache Memory Size
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Hello,

As for Sybase 11, I would like to know if they have the
limit of Cache Memory Size that I can specify when starting
database engine (-c server option), beside the size of
physical memory itself.

Some users told me that when using Sybase 6 back then. The
limit that they can specify is 1500m no matter how much
physical memory
the server has.

Do you still have this kind of limitation in Sybase 11?

Thanks,
Sudarat.


Jeff Albion [Sybase iAnywhere] Posted on 2010-08-11 14:09:32.0Z
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Hi Sudarat,

On 10/08/2010 5:21 PM, SJ wrote:
> As for Sybase 11, I would like to know if they have the
> limit of Cache Memory Size that I can specify when starting
> database engine (-c server option), beside the size of
> physical memory itself.
>
> Some users told me that when using Sybase 6 back then. The
> limit that they can specify is 1500m no matter how much
> physical memory
> the server has.
>
> Do you still have this kind of limitation in Sybase 11?

Beyond physical RAM, the database server is limited to any other memory
restrictions placed on a process by the operating system.

The limitation of ~1500M-1600M as an upper cache limit is a function of
the version 6.0.x server being a 32-bit process. On Windows, the total
32-bit memory space (4GB) is (by default*) split into 2GB/2GB - 2GB for
system space, 2GB for user process space. After loading libraries and
other reserved memory for OS functions, the leftover memory is the 1500M
you see as a hard limit.

*On most newer versions of Windows NT, you can use "/3GB" in the
boot.ini file to switch this split to become 3GB user process / 1GB
system space instead.

---

In the 32-bit world, this limit is overcome with Address Window
Extensions (AWE) - this is enabled using the "-cw" switch on the 32-bit
database server:
http://dcx.sybase.com/index.html#1101en/dbadmin_en11/cw-database-dbserver.html.
This allows the database server to lock read-only table pages in upper
areas of memory beyond the ~1600M for the cache.

In the 64-bit world, this limit is removed, so you are back to using a
maximum of physical RAM found on the system, subject to OS limits.

Regards,

--
Jeff Albion, Sybase iAnywhere

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