On Fri, 2007-10-26 at 14:39 -0700, Jeff Davis wrote: > On Fri, 2007-10-26 at 15:08 -0600, Brian Wipf wrote: > > I have a test PG 8.2.5 installation that has been left idle with no > > connections to it whatsoever for the last 24 hours plus. WALs are > > being archived exactly 5 minutes apart, even though archive_timeout > > is set to 60. Is this the expected behavior for a database with no > > changes? > > > > If it's set to just "60" that means 60 seconds. > > What's happening is that you have a checkpoint_timeout of 5 minutes, and > that checkpoint must write a checkpoint record in the WAL, prompting the > archiving.
archive_timeout is the maximum time to wait for a log switch that contains newly written WAL. That interval is not the same thing as how often WAL records are written. On the idle server a checkpoint is being written every checkpoint_timeout. Then archive_timeout kicks in 60 seconds later, switches the log which then archives that file. Then four minutes later a checkpoint occurs, sees that there is no immediately preceding checkpoint because of the log switch and writes a new checkpoint record. Then 60 seconds later... Overall this produces one WAL file every checkpoint_timeout during idle times, yet without relaxing the guarantee that WAL will be archived every archive_timeout seconds. We *could* force it to perform a log switch whether or not new WAL has been written. If that's what people think is wanted. I'd seen the behaviour as beneficial up til now. -- Simon Riggs 2ndQuadrant http://www.2ndQuadrant.com ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
