Oracle FAQ Your Portal to the Oracle Knowledge Grid

Home -> Community -> Usenet -> c.d.o.server -> Re: 2GB limit of memory for Oracle on WIndows 32 bit

Re: 2GB limit of memory for Oracle on WIndows 32 bit

From: <>
Date: Thu, 28 Jun 2007 23:17:31 +0200
Message-ID: <>

On Thu, 28 Jun 2007 13:04:19 -0700, wrote:

>On Jun 28, 2:15 pm, wrote:
>> On Thu, 28 Jun 2007 01:42:07 -0700, wrote:
>> >When /3GB switch is turned on, will all oracle instances (5 in my
>> >example) still have access only to 3GB memory combined or each
>> >instance will have limit of 3GB memory. Various metalink articels say
>> >this limit to be per instance so I am confused.
>> They are discussing *virtual* memory, not *physical* memory. As soon
>> as a system runs out of *physical* memory, it will swap memory it no
>> longer needs to disk. When this memory is needed again it will be read
>> from disk. This is called a page fault.
>> A disk is a *slow* device.
>> So, please, pray tell me, how desirable do you think it is to
>> configure 3 Gb *per instance*?
>> --
>> Sybrand Bakker
>> Senior Oracle DBA
>If my server has 8GB physical meory, it will be nice to make use of
>8GB instead of restricted only to 3GB. I have seen
>so many articles which talk about 3GB or 2GB per instance
>restriction, but now I am told that is not correct, 3GB or 2GB
>restriction is all instances combined, so it is confusing. Apparently
>there is some restriction related to how much shared memory one can
>allocate on Windows Server, otherwise each instance should be able to
>address 2GB or 3GB (with /3GB switch).

I don't know whether you are a developer or a DBA or a sysadmin. In the latter 2 cases (but also in the first case) you really should try to understand the virtual memory concept. Allocating virtual memory *beyond* physical memory doesn't make sense, as it will force your system to swap.
Even if you would have 8 Gb, it *doesn't make sense* to allocate 3 Gb for every instance, as that will allocate 15 Gb, which is 7 Gb beyond physical RAM. Is that going to work? OF COURSE NOT, as the SYSTEM is GOING TO SWAP LIKE HELL. If you still don't understand this, I would recommend you find a different profession.

Why is it that nowadays IT personell doesn't have a clue about the underlying technology?

Sybrand Bakker
Senior Oracle DBA
Received on Thu Jun 28 2007 - 16:17:31 CDT

Original text of this message