show merge arrows is very slow

i tried the RevisionGraph/'Show merge arrows' feature but it is unusable slow. my repository has 6200 revisions and approx. 10 branches. after i select the Query/'show merge arrows' menu item, it begins to load 'Natural history for...' and this takes over 30 minutes.  is this a known bug? thanks.  os: mac os x 10.6.8 smartsvn: 7.6 preview 2 (build #29)  Java: 1.6.0_51-b11-457-10M4509  os: mac os x 10.6.8 smartsvn: 7.5.5 Java: 1.7.0_10-b18  svnserver: debian wheezy, subversion 1.7 from wandisco i can you provide connection logs