Re: [HACKERS] PG10 transition tables, wCTEs and multiple operationson the same table

On Wed, Jun 7, 2017 at 4:48 PM, Thomas Munro
<thomas.munro@enterprisedb.com> wrote:

> Is there anything about that semantics that is incompatible with the
> incremental matview use case?

Nothing incompatible at all.  If we had separate "new" tables for
UPDATE and DELETE we would logically need to do a "counting"-style
UNION of them just like we will want to do with the OLD (with a
count of -1) and NEW (with a count of 1) to get to a delta now.  So
keeping them separate would be marginally more work for incremental
matview, but not a big deal.

> For example, are the "counting" and
> "DRed" algorithms you've proposed (for non-recursive and recursive
> views) driven entirely by deletions and insertions, so that updates
> look like deletes followed by inserts anyway?

Counting is best done from a "delta" relation which has old and new
combined with opposite counts.  I'm sure that will be fine with
DRed, too.

> If so, I think our
> current treatment of ON CONFLICT DO UPDATE should be fine: you can't
> tell whether the tuples in the new table result from insert or update
> without also consulting the old table, but if the algorithm treats all
> tuples in the old table as deletes (even though in this case they
> result from updates) and all tuples in the new table as inserts (even
> though in this case *some* of them result from updates) anyway then I
> don't think it matters.

I don't think so, either.

--
Kevin Grittner
VMware vCenter Server
https://www.vmware.com/