Re: Global snapshots

On Sat, Jun 20, 2020 at 05:54:18PM +0530, Amit Kapila wrote:
> 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!

Ahsan Hadi <ahsan(dot)hadi(at)highgo(dot)ca> created that page, and I just made a
few wording edits. Ahsan is copying information from this older
sharding wiki page:

https://wiki.postgresql.org/wiki/Built-in_Sharding

to the new one you listed above.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com

The usefulness of a cup is in its emptiness, Bruce Lee