On Fri, 2011-03-18 at 13:16 +0000, MARK CALLAGHAN wrote: > On Fri, Mar 18, 2011 at 9:27 AM, Markus Wanner <mar...@bluegap.ch> wrote: > > Google invented the term "semi-syncronous" for something that's > > essentially the same that we have, now, I think. However, I full > > heartedly hate that term (based on the reasoning that there's no > > semi-pregnant, either). > > We didn't invent the term, we just implemented something that Heikki > Tuuri briefly described, for example: > http://bugs.mysql.com/bug.php?id=7440 > > In the Google patch and official MySQL version, the sequence is: > 1) commit on master > 2) wait for slave to ack > 3) return to user > > After step 1 another user on the master can observe the commit and the > following is possible: > 1) commit on master > 2) other user observes that commit on master > 3) master blows up and a user observed a commit that never made it to a slave > > I do not think this sequence should be possible in a sync replication > system. But it is possible in what has been implemented for MySQL. > Thus it was named semi-sync rather than sync.
Thanks for clearing it up Mark. We should definitely not be calling what we have "semi-sync". The semantics are very different. In PostgreSQL other users cannot observe the commit until an acknowledgement has been received. -- Simon Riggs http://www.2ndQuadrant.com/books/ PostgreSQL Development, 24x7 Support, Training and Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
