Re: prevent immature WAL streaming

On Thu, Oct 14, 2021 at 6:14 PM Amul Sul <sulamul@gmail.com> wrote:
>
> On Wed, Oct 13, 2021 at 10:58 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> >
> > On 2021-Oct-13, Amul Sul wrote:
> >
> > > I have one more question, regarding the need for other global
> > > variables i.e. abortedRecPtr.  (Sorry for coming back after so long.)
> > >
> > > Instead of abortedRecPtr point, isn't enough to write
> > > overwrite-contrecord at XLogCtl->lastReplayedEndRecPtr?  I think both
> > > are pointing to the same location then can't we use
> > > lastReplayedEndRecPtr instead of abortedRecPtr to write
> > > overwrite-contrecord and remove need of extra global variable, like
> > > attached?
> >
> > I'm a bit fuzzy on the difference "the end+1" and "the start of the next
> > record".  Are they always the same?  We do have XLogRecPtrToBytePos()
> > and XLogBytePosToEndRecPtr() to convert unadorned XLogRecPtr values to
> > "usable byte positions", which suggests to me that the proposed patch
> > may fail if end+1 is a page or segment boundary.
> >
>
> Yes, you are correct, that could be a possible failure.
>
> How about calculating that from the lastReplayedEndRecPtr by
> converting it first to "usable byte positions" and then recalculating
> the record pointer from that, like attached?
>

Any thoughts about the patch posted previously?

Regards,
Amul