Denys writes:

< snip >

> That is what to which I took exception.  I explained to Mr. Lalley that
> his understanding was faulty.  XM did not scan main memory during a
> checkpoint.  It only posted the pages contained in the XM log files to
> the various disk drives in the volume set being checkpointed.  Now,
> whether there are one or two logfiles is totally irrelevant to that
> discussion.  My point was to dispel the fantasy being perpetrated by Mr.
> Lalley and now being reinforced by Bill C.

My apologies... I was responding only to the most recent post and not to the
entire thread which I have to admit, I missed.

Yes, there are two logs per volume set, the system log and the user log, each
has two halves. One trigger for a checkpoint is when a loghalf fills. Another
trigger is when there are too many pages of XM-protected file objects frozen
in memory. There are a couple other triggers that I can't recall at the moment.

No, XM does not scan all of memory at a checkpoint. It maintains a list of
files (GUFD's) that have changed in a particular log half. A "dirty page" can
occur outside of XM, obviously,  all XM cares about are the pages of objects
it has to protect.

Cheers,

Bill
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