It does not work as advertised, in AIX either... I played with this in AIX 5L.
- Kirti
- "Hately, Mike (LogicaCMG)" <mike.hately_at_nedl.co.uk> wrote:
> Stephen,
>
> The documentation is pretty wooly regarding this issue but the way it seems
> to be intended to work is this:
> At startup Oracle will allocate an SGA sized as specified in the
> sga_max_size parameter. This is to ensure that the system has enough memory
> accomodate what you see as a maximum requirement for the SGA.
> After it's allocated this and started the database it should deallocate any
> memory it holds over and above that required to store the components of the
> SGA. In some platforms/versions this deallocation doesn't occur. Solaris for
> example behaves like this unless you move to version 8.
> It's possible that your version of Tru64 has a similar limitation or that
> you're seeing a bug.
> To my mind though, Oracle Support's claim that this is expected behaviour is
> a bit of a cop out. This is certainly not the way it was supposed to work.
> The concept guide states the following:
>
> "The SGA can grow in response to a database administrator statement, up to
> an operating system specified maximum and the SGA_MAX_SIZE specification."
>
> and
>
> "Oracle can start instances underconfigured and allow the instance to use
> more memory by growing the SGA components, up to a maximum of SGA_MAX_SIZE"
>
> Both of these statements imply that the unused memory is supposed to be
> released back to the operating system.
> The way that this feature operates on your system it allows you to juggle
> storage backwards and forwards between caches which is still useful but not
> 'what it says on the box'.
>
> I'd ask Oracle under what cirtcumstances this is normal behaviour. It's not
> the way the software is intended to work so maybe it's a platform
> limitation.
>
> In order to give you a better idea of what Oracle thinks it's SGA is using
> you can query the following views :
>
> - V$SGA_CURRENT_RESIZE_OPS:
> Information about SGA resize operations that are currently in progress.
> An operation can be a grow or a shrink of a dynamic SGA component.
>
> - V$SGA_RESIZE_OPS:
> Information about the last 100 completed SGA resize operations.
> This does not include any operations currently in progress.
>
> - V$SGA_DYNAMIC_COMPONENTS: Information about the dynamic components in
> SGA.
> This view summarizes information based on all completed SGA resize
> operations since startup.
>
> - V$SGA_DYNAMIC_FREE_MEMORY:
> Information about the amount of SGA memory available for future dynamic
> SGA resize operations.
>
>
> Hope this helps,
> Mike Hately
>
>
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Received on Fri Aug 01 2003 - 13:19:37 CDT