Re: Pluggable storage

On Fri, Oct 13, 2017 at 11:55 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Thu, Oct 12, 2017 at 8:00 PM, Haribabu Kommi
> <kommi(dot)haribabu(at)gmail(dot)com> wrote:
> > Currently I added a snapshot_satisfies API to find out whether the tuple
> > satisfies the visibility or not with different types of visibility
> routines.
> > I feel these
> > are some how enough to develop a different storage methods like UNDO.
> > The storage methods can decide internally how to provide the visibility.
> >
> > + amroutine->snapshot_satisfies[MVCC_VISIBILITY] =
> HeapTupleSatisfiesMVCC;
> > + amroutine->snapshot_satisfies[SELF_VISIBILITY] =
> HeapTupleSatisfiesSelf;
> > + amroutine->snapshot_satisfies[ANY_VISIBILITY] = HeapTupleSatisfiesAny;
> > + amroutine->snapshot_satisfies[TOAST_VISIBILITY] =
> HeapTupleSatisfiesToast;
> > + amroutine->snapshot_satisfies[DIRTY_VISIBILITY] =
> HeapTupleSatisfiesDirty;
> > + amroutine->snapshot_satisfies[HISTORIC_MVCC_VISIBILITY] =
> > HeapTupleSatisfiesHistoricMVCC;
> > + amroutine->snapshot_satisfies[NON_VACUUMABLE_VISIBILTY] =
> > HeapTupleSatisfiesNonVacuumable;
> > +
> > + amroutine->snapshot_satisfiesUpdate = HeapTupleSatisfiesUpdate;
> > + amroutine->snapshot_satisfiesVacuum = HeapTupleSatisfiesVacuum;
> >
> > Currently no changes are carried out in snapshot logic as that is kept
> > seperate
> > from storage API.
>
> That seems like a strange choice of API. I think it should more
> integrated with the scan logic. For example, if I'm doing an index
> scan, and I get a TID, then I should be able to just say "here's a
> TID, give me any tuples associated with that TID that are visible to
> the scan snapshot". Then for the current heap it will do
> heap_hot_search_buffer, and for zheap it will walk the undo chain and
> return the relevant tuple from the chain.

OK, Understood.
I will check along these lines and come up with storage API's.

Regards,
Hari Babu
Fujitsu Australia