Enabling memory windows

[Gerry Tully]

I have an N-Class system with 4 databases and a SGA of less than 1.75gb. Would there be any benefit to enabling memory windows or would I see no difference? The system has 4 550mHZ processors and 6gb ram. Thanks.

[A. Clay Stephenson · Accepted solution]

Hi Gerry:

If these are 64-bit applications there is no point in doing it; if these are 32-bit apps and you want one or maybe two of these instances to have a larger SGA then maybe.

[Bill Hassell]

The advantage of memory wondows is in not having to fight with memory fragmentation that occurs in the primary memory window. In other words, all 4 instances of your database will request some amount for SGA (generally more is better) and if there is not a contiguous block of the requested size, then Oracle will report not enough memory.

By running each instance in its own window, the entire 32bit addressing space will be clean and available for maximum allocation (ie, SGA = 1700 megs if desired). Note that you need all the patches to enable memory windows on 11.0, and to avoid excessive swapping, you should provide enough RAM to hold all the SGA sizes pkus all the programs and a few hundred megs of buffer cache.

If RAM isn't large enough, all the advantages of memory windows will be erased with swapping.