While browsing docs.hp.com,  I came across the online documentation (Thanks
HP, I'm sure that the trees of the world thank you as well!) for long
awaited and much kept under wraps, Master Dynamic eXpansion (MDX) feature.

http://docs.hp.com/dynaweb/smpe/b1019/b840/@Generic__BookTextView/30148;hf=o

What is not clear is why the master dataset is only expanded when it is
"almost full"! And, what the definition of "almost" is. This seriously
negates the value of this feature because many systems start to encounter
performance problems long before their master data sets get anywhere near
full! I have seen clustering erupt into a performance issue even in the %65
full levels.(yes, they did have prime capacities)

To further negate performance, once MDX is triggered, a 'Quick search' is
done for each DBput in the original (almost full) area to attempt to place
the entry. This assumes that some DBeletes have been done.

It seems to me that MDX should have been implemented using the 'Quick
search' from the beginning to see if the secondary can be placed in the same
prefetch as the primary. If it can't, meaning I have to do another IO
anyway, then place it in the expanded area.

I know that this deviates from the DDX design and implementation but given
the overall implications I think a change is required. Otherwise, this
'feature' will only be applicable to very small master datasets that usually
wouldn't require MDX anyway.

Mike Hornsby

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