On 6 April 2016 at 10:09, Andres Freund <and...@anarazel.de> wrote: > On 2016-04-06 10:04:42 +0100, Simon Riggs wrote: > > On 6 April 2016 at 09:45, Andres Freund <and...@anarazel.de> wrote: > > > > > On 2016-04-06 09:18:54 +0100, Simon Riggs wrote: > > > > Rather than take that option, I went to the trouble of writing a > patch > > > that > > > > does the same thing but simpler, less invasive and more maintainable. > > > > Primarily, I did that for you, to avoid you having wasted your time > and > > > to > > > > allow you to backpatch a solution. > > > > > > But it doesn't. It doesn't solve the longstanding problem of > checkpoints > > > needlessly being repeated due to standby snapshots. > > > <sigh> I can't see why you say this. I am willing to listen, but this > > appears to be wrong. > > The issue there is that we continue to issue checkpoints if the only > activity since the last checkpoint was emitting a standby > snapshot. That's because: >
I agree this is the current situation in 9.4 and 9.5, hence the bug report. This no longer occurs with the patches I have proposed. The snapshot is skipped, so a further checkpoint never triggers. > The proposed patch allows to fix that in a more principled manner, > because we can simply check that no "important" records have been > emitted since the last checkpoint, and skip if that's the case. I understand the proposal you have made. The patch to implement it is what I object to; my comments made last Sunday. > > What issue is that? Previously you said it must not skip it at all for > > logical. > > It's fine to skip the records iff nothing important has happened since > the last time a snapshot has been logged. Again, the proposed approach > allowed to detect that. Agreed, both proposals do that. > > > We now log more WAL with > > > XLogArchiveTimeout > 0 than without. > > > And the problem with that is what? > > That an idle system unnecessarily produces WAL? Waking up disks and > everything? > The OP discussed a problem with archive_timeout > 0. Are you saying we should put in a fix that applies whatever the setting of archive_timeout? Are we concerned that a master sends a small amount of data every few minutes to a standby it is connected to? I hadn't read that in the thread. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
