Re: Implementing Incremental View Maintenance

Hi Greg,

On Wed, 3 Apr 2019 17:41:36 -0400
Greg Stark <stark(at)mit(dot)edu> wrote:

> On Sun, 31 Mar 2019 at 23:22, Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp> wrote:
> >
> > Firstly, this will handle simple definition views which includes only
> > selection, projection, and join. Standard aggregations (count, sum, avg,
> > min, max) are not planned to be implemented in the first patch, but these
> > are commonly used in materialized views, so I'll implement them later on.
>
> It's fine to not have all the features from day 1 of course. But I
> just picked up this comment and the followup talking about splitting
> AVG into SUM and COUNT and I had a comment. When you do look at
> tackling aggregates I don't think you should restrict yourself to
> these specific standard aggregations. We have all the necessary
> abstractions to handle all aggregations that are feasible, see
> https://www.postgresql.org/docs/devel/xaggr.html#XAGGR-MOVING-AGGREGATES
>
> What you need to do -- I think -- is store the "moving aggregate
> state" before the final function. Then whenever a row is inserted or
> deleted or updated (or whenever another column is updated which causes
> the value to row to enter or leave the aggregation) apply either
> aggtransfn or aggminvtransfn to the state. I'm not sure if you want to
> apply the final function on every update or only lazily either may be
> better in some usage.

Thank you for your suggestion! I submitted the latest patch just now supporting
some aggregate functions, but this supports only sum and count, and lacking a
kind of generalization. However, I would like to refine this to support more
general aggregate functions. I think your suggestions is helpful for me to do
this. Thank you!

Best regards,
Yugo Nagata

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>