Michael writes:
>   I haven't looked at the Communicator article yet, but could
> it possibly be talking about the use of the 'DSEM' setting in
> DBUTIL?  If so, then what this means is that within any Image
> database, all datasets that are logically related (via set paths)
> are considered an atomic unit when placing a lock on the
> associated master dataset.

The term "lock" in this case doee not mean the kind of locks applied with
DBLOCK.  It refers to the internal Image semaphores (the "SEM" in DSEM)
which are used internally to control access to Image's own data structures.

Image used to have one semaphore for the whole database and there were
certain operations which required locking this briefly.  This probably
wasn't a very big issue for single CPU systems, since the semaphore wasn't
held all that long, but for very busy systems and especially for multi-CPU
boxes, the DSEM option can get you more throughput.

The question about whether there is any downside to turning on "DSEM" was
asked at SigImage at HP World and I believe the answer was essentially
that there is absolutely no downside to turning DSEM on, unless there are
bugs in it that haven't been discovered yet.  The only reason it defaults
to off is probably Image's historically conservative approach to enabling
new functionality.  Perhaps a future Image release will always enable
this functionality.

This points out a problem with new features like this.  They generally have
a flag in the root file only indicating whether the feature is enabled or
disabled.  I suggest that there should be a third option called "default"
which means that Image should do what it thinks is best.  This way a new
feature can be introduced and for a while the default action would be to
disable the feature, then later the default could be changed to enable the
feature for all databases.  A user could at any time change the flag from
"default" to "enabled" or "disabled", giving complete control over the
feature.  DBUTIL SHOW would indicate which features were set to "default"
and what the default value actually was for that Image version.  This
would allow HP to start out conservatively, then once the new feature has
proven to be safe, all databases (except those that specifically disable
the feature) would automatically start taking advantage of it when the
user upgraded to a new release.

G.