2004

694 | Chapter 23 Reference Other Drawing Files (Xrefs)
To use the xref log file
1 At the Command prompt, enter xrefctl.
2 Enter 1 to turn logging on or 0 to turn logging off.
3 Press
ENTER.
Logging is off by default.
Increase Performance with Large Xrefs
There are several features that can improve performance with large external
references.
Overview of Demand Loading
AutoCAD uses demand loading and saving drawings with indexes to increase
performance with large external references that have been clipped using
AutoCAD or that have many objects on frozen layers. With demand loading,
AutoCAD loads into memory only the data from the reference drawing that
is necessary to regenerate the current drawing. In other words, referenced
material is read in “on demand.” Demand loading works in conjunction with
the
INDEXCTL, XLOADCTL, and XLOADPATH system variables.
Unload Xrefs
When an xref is unloaded from the current drawing, the drawing opens
much faster and uses less memory. The xref definition is unloaded from the
drawing file, but the pointer to the reference drawing remains. The xref is not
displayed, and nongraphical object information does not appear in the draw-
ing. However, you can restore all the information by reloading the xref. If
XLOADCTL (demand loading) is set to 1, unloading the drawing unlocks the
original file.
You should unload a reference file if it is not needed in the current drawing
session but may be used later for plotting. You can maintain a working list of
unloaded xrefs in the drawing file that you can load as needed.