Thor/Merlin 4.5:
Datatree merging and garbage collection
Datatree merging
In Thor databases, data is added to existing datatrees by "tree merging"
via the
dt_thor_tdtmerge() method.
The implementation of this method has changed in 4.51.
Except for providing higher performance, this change should be
invisible to users and programmers.
Old method
Previously, tree-merging was done by the client process
rather than the thorserver.
(Thor toolkit programmers didn't have to be aware of this, since
the toolkit takes care of all such things.)
Also, merged datatrees were always written to the end of the database
file, leaving "holes" in the file which were recovered by "crunching".
The advantage of this method was that it allowed the thorserver to
be very simple (thorserver didn't have to know very much about datatrees).
The disadvantage of this method is that it is slow:
it requires three network transactions to perform a merge (~15 mS).
The old method is illustrated below:
New method
In Release 4.5, we are introducing a "smarter" thorserver which is
able to merge datatrees locally.
The new method for datatree merging allows the client to pass datatrees
to be merged to the server which then handles the rest of the task locally.
This allows datatree merging to be done with a single network transaction.
The 4.5 thorserver is also "smarter" about replacing datatrees in
database files: datatrees are replaced "in-place" if they'll fit,
reducing the amount of automatic database crunching required (which
is another slow step). To make this more effective, extra reserved
space is inserted following commonly-used cross-references in an
adaptive manner. Such space is not subject to garbage collection
(except when the database is explicitly crunched).
This change in a fundamental Thor method is entirely invisible to
users and programmers alike.
Such behavior is a consequence of the "transparent object interface"
used by the Daylight Toolkit.
(Ya gotta love it, ain't OOP grand?)
Daylight Chemical Information Systems, Inc.
info@daylight.com
