RE: AS400/i5 etc general behaviour

["Walden H. Leverich" <WaldenL@xxxxxxxxxxxxxxx>]

> The difference between the single level store the i uses and the swap
> file system used by other systems, is that when the i swaps data out
> of memory, it only exists in one place on disk.  Whereas with other
> systems, data is swapped out of memory into a specific swap file on
> disk plus the original copy of the data still resides on the file
> system.

That really depends on the nature of the page being swapped out. Say you
fault in a page of an RPG program, and then the machine needs to use
that memory elsewhere, the i will simply drop that page on the floor
since it knows it can read that page from disk again. BTW, other OSs
will do that too. If Windows needs to swap out a DLL it will simply drop
it on the floor, it doesn't need to save it to the swap file.

However, if the memory page you're working with has modifications then
the i has to swap that page out to some sort of swap file as it can't
reload it from disk as the changes haven't made it to disk yet (and
might not ever do so). Likewise, if you've changed a page in memory on
Windows and windows needs that memory it has no choice but to write it
out to swap.

Of course, the nature of i programming makes it less likely you'll
modify pages of information as most things can't be changed by a
programmer.

-Walden