🚀 go-pugleaf

pcg@odin.cs.aber.ac.uk (Piercarlo Grandi) writes:

>Let me disagree. Unfortunately almost all databases for which a
>mainframe is worth having are so immense that their working set is
>always much larger than real memory available.

You misunderstand.  I do not refer to keeping things resident.  Query
optimization, for instance has to do with minimizing search paths, not
optimizing use of fast store (although good query optimizers do figure
in costs of network latencies).  If your database is large, you might
concern yourself with avoiding unnecessary search components.  For
another example, deferred writes have to do with the timing
characteristics of disks, such as the interesting fact that it costs
about as much to write a byte as it does to write a bunch of them.  If
your database is large and active, you might find this method
worthwhile.  Neither method depends on large memory with respect to
database size.  Thus either would be particularly appropriate for cases
where the opposite will always be true.

Perhaps I misled you by my mention of the memory costs of avoiding
i/o.  This is simply a reference to the space required to store the
code that computes the query execution plan, the data that's waiting
to synchronize a table update with a committed logged write, and so
on.  None of this space represents storage for the database at any
time.  Buffering, for instance, might count as such.

-- Jon
-- 
Jonathan Krueger    jkrueger@dtic.dla.mil   uunet!dgis!jkrueger
The Philip Morris Companies, Inc: without question the strongest
and best argument for an anti-flag-waving amendment.