Using svn for portfile management

Hi, As an occasional Portfile editor, I prefer to use svn to manage Portfiles than rsync because that allow me to check diffs or changelogs easily. One problem is PortIndex. Everytime I port update to get the latest port tree, I have to rebuild, which takes a long time to finish. Is there any easier way of doing this job? I'm using a bit old Mac, doing portindex everytime is not a easy job. Thanks.