On Fri, 2010-09-03 at 12:33 +0300, Heikki Linnakangas wrote: > On 03/09/10 10:45, Simon Riggs wrote: > > On Fri, 2010-09-03 at 09:55 +0300, Heikki Linnakangas wrote: > >> On 03/09/10 09:36, Simon Riggs wrote: > >>> On Fri, 2010-09-03 at 12:50 +0900, Fujii Masao wrote: > >>>> That design would affect what the standby should reply. If we choose > >>>> async/recv/fsync/replay on a per-transaction basis, the standby > >>>> should send multiple LSNs and the master needs to decide when > >>>> replication has been completed. OTOH, if we choose just sync/async, > >>>> the standby has only to send one LSN. > >>>> > >>>> The former seems to be more useful, but triples the number of ACK > >>>> from the standby. I'm not sure whether its overhead is ignorable, > >>>> especially when the distance between the master and the standby is > >>>> very long. > >>> > >>> No, it doesn't. There is no requirement for additional messages. > >> > >> Please explain how you do it then. When a commit record is sent to the > >> standby, it needs to acknowledge it 1) when it has received it, 2) when > >> it fsyncs it to disk and c) when it's replayed. I don't see how you can > >> get around that. > >> > >> Perhaps you can save a bit by combining multiple messages together, like > >> in Nagle's algorithm, but then you introduce extra delays which is > >> exactly what you don't want. > > > >> From my perspective, you seem to be struggling to find reasons why this > > should not happen, rather than seeing the alternatives that would > > obviously present themselves if your attitude was a positive one. We > > won't make any progress with this style of discussion. > > Huh? You made a very clear claim above that you don't need additional > messages. I explained why I don't think that's true, and asked you to > explain why you think it is true. Whether the claim is true or not does > not depend on my attitude.
Why exactly would we need to send 3 messages when we could send 1? Replace your statements of "it needs to" with "why would it" instead. -- Simon Riggs www.2ndQuadrant.com 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