Re: Global snapshots

On Fri, Jun 19, 2020 at 6:33 PM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
> On Fri, Jun 19, 2020 at 05:03:20PM +0800, movead(dot)li(at)highgo(dot)ca wrote:
> >
> > >> would like to know if the patch related to CSN based snapshot [2] is a
> > >> precursor for this, if not, then is it any way related to this patch
> > >> because I see the latest reply on that thread [2] which says it is an
> > >> infrastructure of sharding feature but I don't understand completely
> > >> whether these patches are related?
> > >I need some time to study this patch.. At first sight it is different.
> >
> > This patch[2] is almost base on [3], because I think [1] is talking about 2PC
> > and FDW, so this patch focus on CSN only and I detach the global snapshot
> > part and FDW part from the [1] patch.
> >
> > I notice CSN will not survival after a restart in [1] patch, I think it may not
> > the
> > right way, may be it is what in last mail "Needs guarantees of monotonically
> > increasing of the CSN in the case of an instance restart/crash etc" so I try to
> > add wal support for CSN on this patch.
> >
> > That's why this thread exist.
>
> I was certainly missing how these items fit together. Sharding needs
> parallel FDWs, atomic commits, and atomic snapshots. To get atomic
> snapshots, we need CSN. This new sharding wiki pages has more details:
>
> https://wiki.postgresql.org/wiki/WIP_PostgreSQL_Sharding
>

Thanks for maintaining this page. It is quite helpful!

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com