Re: archive status ".ready" files may be created too early

On 2021-Aug-18, Bossart, Nathan wrote:

> As long as XLogBackgroundFlush() found work to do, it would take care
> of notifying, but I don't think we can depend on that.  However, since
> we're primarily using the WAL writer to take care of the case when the
> record has already been flushed, notifying beforehand seems fine to
> me.  If XLogBackgroundFlush() does end up calling XLogWrite(), it'll
> call it again, anyway.

Agreed.

> In the attached patch, I modified XLogInsertRecord() to simply set the
> latch if we detect that flushRecPtr has advanced.

Right, that's what I was thinking.  I modified that slightly to use
LogwrtResult.Flush (which should be fresh enough) instead of calling
GetFlushRecPtr again, which saves a bit.  I also changed it to > instead
of >=, because if I understand you correctly we only care to notify if
the flush pointer advanced, not in the case it stayed the same.

I made a few other cosmetic tweaks -- added comment to
SegmentBoundaryEntry and renamed the 'pos' to 'endpos'; renamed argument
'notify' of XLogArchiveNotify to 'nudge' (because having two different
"notify" concepts in that function seemed confusing).

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/
"It takes less than 2 seconds to get to 78% complete; that's a good sign.
A few seconds later it's at 90%, but it seems to have stuck there.  Did
somebody make percentages logarithmic while I wasn't looking?"
                http://smylers.hates-software.com/2005/09/08/1995c749.html