On 2015-11-04 16:01:28 +0900, Michael Paquier wrote: > On Wed, Nov 4, 2015 at 8:39 AM, Andres Freund <and...@anarazel.de> wrote: > > On November 4, 2015 12:37:02 AM GMT+01:00, Michael Paquier wrote: > >>On a completely idle system, I don't think we should log any standby > >>records. This is what ~9.3 does. > > > > Are you sure? I think it'll around checkpoints, no? I thought Heikki had > > fixed that, but looking sound that doesn't seem to be the case. > > Er, yes, sorry. I should have used clearer words: I meant idle system > with something running nothing including internal checkpoints.
Uh, but you'll always have checkpoints happen on wal_level = hot_standby, even in 9.3? Maybe I'm not parsing your sentence right. As soon as a single checkpoint ever happened the early-return logic in CreateCheckPoint() will fail to take the LogStandbySnapshot() in CreateCheckPoint() into account. The test is: if (curInsert == ControlFile->checkPoint + MAXALIGN(SizeOfXLogRecord + sizeof(CheckPoint)) && ControlFile->checkPoint == ControlFile->checkPointCopy.redo) which obviously doesn't work if there's been a WAL record logged after the redo pointer has been determined etc. The reason that a single checkpoint is needed to "jumpstart" the pointless checkpoints is that otherwise we'll never have issued a LogStandbySnapshot() and thus the above code block works if we started from a proper shutdown checkpoint. Independent of the idle issue, it seems to me that the location of the LogStandbySnapshot() is actually rather suboptimal - it really should really be before the CheckPointGuts(), not afterwards. As closer it's to the redo pointer of the checkpoint a hot standby node starts up from, the sooner that node can reach consistency. There's no difference for the first time a node starts from a basebackup (since we gotta replay that checkpoint anyway before we're consistent), but if we start from a restartpoint... Greetings, Andres Freund -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers