How to update a sparse directory?

Hi,

We're using SVN version 1.8.19 on Red Hat Enterprise Linux 6.8 .

For one of our projects, the SVN area is a sparse directory. I'm
wondering what's the best way to update that directory?

I've searched the web but haven't found a definitive answer to how to
_update_ a sparse directory.

Should I do an "svn update" at the root directory, and then traverse the
lower levels and do updates as well?

Based on a web answer, I thought "svn update *" at the root level would
work; but it turns out that it doesn't actually update all directories
(at least, not in my case).

Regards,

-- 
Mun