System Variables

There are many system variables which can affect the performance of running Lisp code ... many are already well-known, some are less known to have performance impact. So it is useful to set specific system variables to defined state to improve performance and to prevent side-effects.

CMDECHO	set as 0 does not only suppress unwanted output to commandline; many commands format a prompt string which is finally not used (string processing is rather slow)
OSMODE	set as 0 calculating snap points can be slow, and snapping is mostly unwanted during Lisp runtime; any point input by (command) or (vl-cmdf) is fully processed by object snapping !
DRAGMODE	set as 0 suppresses generation of temporary drag graphics for several commands
PICKSTYLE	set as 0 (unless you explicitly want the group entities to be included) disable group + associative hatch selection during entity selection; this is most important : if a drawing has groups, all group entities are verified against entities in primary selectionset; this can be very costly when a drawing has many groups and/or the primary selectionset
HIGHLIGHT	set as 0 to disable highlighting of objects when using (command)
UCSICON	set as 0 disable ucsicon display while Lisp code is running (reduces flickering, and updating temp. graphics is not fast)
UCSFOLLOW	set as 0 to prevent the actual view from following any ucs change (keeps redraw times small)
UCSDETECT	set as 0 prevent dynamic ucs changes, usually unwanted while Lisp code runs
AUTOSNAP	set as 0 disable any visual effects related to snapping (markers, tooltips, magnets etc.)
BLIPMODE	set as 0 do not draw temporary point markers
LOGFILEMODE	set as 0 disables recording of operations to logfile
REGENMODE	set as 0 turns off automatic regeneration triggered by several commands
SOLIDCHECK	set as 0 reduce any potential overhead when creating + modifying ACIS objects
SNAPMODE	set as 0 disable cursor snapping to reduce internal processing of input points
SELECTIONPREVIEW	set as 0 disable highlighting of entities

Of course, the majority of these system variables are effective in combinations with (command) only, not with API calls.
Nevertheless, it is a good habit to set desired system variables and restore them,
When the Lisp program switches to interactive user-input / operations, any changed system variables should be switched back to previous or appropriate settings.

Changing System Variables

System variables are often changed by (command "<sysvar-name") as each system variable is also available as a command name.

Highly recommended : never use (command "<sysvar-name") to change system variables - always use (setvar ""<sysvar-name" value) instead.

Execution of (command) is relatively slow, it has several side-effects which cost performance, like triggered command reactors, implied GUI updates, error status can not be retrieved and so on.