Hello.
# Sorry, I wrongly thought that I replied to this thread..
At Tue, 7 Jul 2020 09:02:56 +0000, "matsumura.ryo@fujitsu.com" <matsumura.ryo@fujitsu.com> wrote in
> At Monday, July 6, 2020 05:13:40 +0000, "Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>" wrote in
> > > > after WAL buffer is filled up to the requested position. So when it
> > > > crosses segment boundary we know the all past corss segment-boundary
> > > > records are stable. That means all we need to remember is only the
> > > > position of the latest corss-boundary record.
> > >
> > > I could not agree. In the following case, it may not work well.
> > > - record-A and record-B (record-B is a newer one) is copied, and
> > > - lastSegContRecStart/End points to record-B's, and
> > > - FlushPtr is proceeded to in the middle of record-A.
> >
> > IIUC, that means record-B is a cross segment-border record and we hav e
> > flushed beyond the recrod-B. In that case crash recovery afterwards
> > can read the complete record-B and will finish recovery *after* the
> > record-B. That's what we need here.
>
> I'm sorry I didn't explain enough.
>
> Record-A and Record-B are cross segment-border records.
> Record-A spans segment X and X+1
> Record-B spans segment X+2 and X+3.
Ok.
> If both records have been inserted to WAL buffer, lastSegContRecStart/End points to Record-B.
> If a writer flushes upto the middle of segment-X+1, NotifyStableSegments() allows the writer to notify segment-X.
> Is my understanding correct?
I think that that cannot happen since the segment X must have been
flushed at the time Record-A is completely flushed out. When we write
to the next segment, we have already flushed and closed the whole last
segment. If it is not the case we are to archive segment files not
fully flushed, and would get broken archive files.
Am I missing something here?
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center