On Fri, Jul 1, 2011 at 3:25 AM, Robert Haas <robertmh...@gmail.com> wrote: > On Thu, Jun 30, 2011 at 1:51 PM, Kevin Grittner > <kevin.gritt...@wicourts.gov> wrote: >> I think doing anything in PostgreSQL around this beyond allowing >> DBAs to trust their server clocks is insane. The arguments for >> using and trusting ntpd is pretty much identical to the arguments >> for using and trusting the OS file systems. > > Except that implementing our own file system would likely have more > benefit and be less work than implementing our own time > synchronization, at least if we want it to be reliable. > > Again, I am not trying to pretend that this is any great shakes. > MySQL's version of this feature apparently does somehow compensate for > time skew, which I assume must mean that their replication works > differently than ours - inter alia, it probably requires a TCP socket > connection between the servers. Since we don't require that, it > limits our options in this area, but also gives us more options in > other areas. Still, if I could think of a way to do this that didn't > depend on time synchronization, then I'd be in favor of eliminating > that requirement. I just can't; and I'm inclined to think it isn't > possible. > > I wouldn't be opposed to having an option to try to detect time skew > between the master and the slave and, say, display that information in > pg_stat_replication. It might be useful to have that data for > monitoring purposes, and it probably wouldn't even be that much code. > However, I'd be a bit hesitant to use that data to "correct" the > amount of time we spend waiting for time-delayed replication, because > it would doubtless be extremely imprecise compared to real time > synchronization, and considerably more error-prone. IOW, what you > said.
I agree with Robert. It's difficult to implement time-synchronization feature which can deal with all the cases, and I'm not sure if that's really worth taking our time. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
