The mod_dav_svn module goes through a lot of work to make sure that data you've marked “unreadable” doesn't get accidentally leaked. This means that it needs to closely monitor all of the paths and file-contents returned by commands like svn checkout or svn update commands. If these commands encounter a path that isn't readable according to some authorization policy, then the path is typically omitted altogether. In the case of history or rename tracing—e.g. running a command like svn cat -r OLD foo.c on a file that was renamed long ago—the rename tracking will simply halt if one of the object's former names is determined to be read-restricted.

All of this path-checking can sometimes be quite expensive, especially in the case of svn log. When retrieving a list of revisions, the server looks at every changed path in each revision and checks it for readability. If an unreadable path is discovered, then it's omitted from the list of the revision's changed paths (normally seen with the --verbose option), and the whole log message is suppressed. Needless to say, this can be time-consuming on revisions that affect a large number of files. This is the cost of security: even if you haven't configured a module like mod_authz_svn at all, the mod_dav_svn module is still asking Apache httpd to run authorization checks on every path. The mod_dav_svn module has no idea what authorization modules have been installed, so all it can do is ask Apache to invoke whatever might be present.

On the other hand, there's also an escape-hatch of sorts, one which allows you to trade security features for speed. If you're not enforcing any sort of per-directory authorization (i.e. not using mod_authz_svn or similar module), then you can disable all of this path-checking. In your httpd.conf file, use the SVNPathAuthz directive:

<Location /repos>
  DAV svn
  SVNParentPath /var/svn

  SVNPathAuthz off
</Location>
          

The SVNPathAuthz directive is “on” by default. When set “off”, all path-based authorization checking is disabled; mod_dav_svn stops invoking authorization checks on every path it discovers.