On Wed, 2008-12-10 at 15:06 -0500, Aidan Van Dyk wrote: > Call me think, but I'm confused... In sync rep, there *can't be* any > catchign up do do... i.e. if the "slave" isn't accepting the WAL the > master "stops" doing *anything*...
In normal/steady state, yes, you are correct. But there is more... The simplest way to configure standby would be to freeze the primary while we setup the standby and then go straight into normal/steady state. That could mean hours of downtime for large databases, which is unacceptable in a feature aimed at increasing availability. So we need to allow the primary to continue working while the standby is setup. That then creates a log gap between the LSN of the primary and the LSN of the standby, which must be resolved. So the catchup occurs during the transient initial phase when standby is catching up with primary before they continue together in normal/steady state. Most of the architectural discussion over last few months has been about the need for the initial state and how to handle it. Most of the code complexity also. -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
