The dbcdup command duplicates the cursor, creates a new cursor
that uses the same transaction and locker ID as the original cursor. This
is useful when an application is using locking and requires two or more
cursors in the same thread of control.
The options are as follows:
-position
The newly created cursor is initialized to reference the same position in
the database as the original cursor and hold the same locks. If the
-position flag is not specified, then the created cursor is
uninitialized and will behave like a cursor newly created using the
dbcursor command.
The dbcdup command returns 0 on success, and in the case of error, a Tcl error
is thrown.