Comment 0 for bug 288910

See http://code.google.com/p/google-mysql-tools/wiki/SemiSyncReplication

There's a version in a MySQL 6.0 (from code provided to MySQL), this could be backported to 5.1 (or even 5.0), or the original code extracted from the big Google patches again. Backporting might make more sense, if the 6.0 code is ok.