Re: AS400/i5 etc general behaviour

[Charles Wilt <charles.wilt@xxxxxxxxx>]

On Fri, Mar 13, 2009 at 5:48 PM, Tom Liotta <qsrvbas@xxxxxxxxxxxx> wrote:
> Charles Wilt wrote:
>
> > 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. In other words, with the i, a particular piece of data exists
> > at a given time either on disk, or in memory.
>
> Shouldn't that be "...with the i, a particular piece of data exists
> at a given time either on disk, or on disk _and_ in memory."? I
> don't think it's wiped from disk when it's paged into memory. I
> think it's more that whenever it's paged into memory, that becomes
> the page-image that everything (most things?) recognize as the "real
> thing". And unless it actually changes, it shouldn't ever be paged
> back out.

Of course the object page isn't wiped from disk, but for all practical
purposes it doesn't exist as long as the page is in memory.  Some
other job can't come along and access the object's page on disk.  In
contrast, with other OS's disk based file systems another program can
access the original data on disk.

Just because the system doesn't waste time wiping the page from disk,
doesn't mean it's still there.  When you delete a record, the system
doesn't wipe the record and condense the file.  But you wouldn't
consider the record still there would you?

Charles