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From: Kirill Reshke <reshkekirill@gmail.com>
Date: Sat, 27 Jul 2024 13:26:46 +0500
Message-ID: <CALdSSPhj1H1NS7QiYkSQNCksPCwjtLcyt3==evgkBX1SrKyVdQ@mail.gmail.com>
Subject: Re: Incremental View Maintenance, take 2
To: Yugo NAGATA <nagata@sraoss.co.jp>
Cc: Peter Smith <smithpb2250@gmail.com>, jian he <jian.universality@gmail.com>, 
	Tatsuo Ishii <ishii@sraoss.co.jp>, pgsql-hackers@postgresql.org
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Precedence: bulk

Hi!
Cloudberry DB (Greenplum fork) uses IMMV feature for AQUMV (auto query
use matview) feature, so i got interested in how it is implemented.

On Thu, 11 Jul 2024 at 09:24, Yugo NAGATA <nagata@sraoss.co.jp> wrote:
>
> I updated the patch to bump up the version numbers in psql and pg_dump codes
> from 17 to 18.

Few suggestions:

1) `Add-relisivm-column-to-pg_class-system-catalog` commit message
should be fixed, there is "isimmv" in the last line.
2) I dont get why `Add-Incremental-View-Maintenance-support.patch`
goes after 0005 & 0004. Shoulndt we first implement feature server
side, only when client (psql & pg_dump) side?
3) Can we provide regression tests for each function separately? Test
for main feature in main patch, test for DISTINCT support in
v34-0007-Add-DISTINCT-support-for-IVM.patch etc? This way the patchset
will be easier to review, and can be committed separelety.
4) v34-0006-Add-Incremental-View-Maintenance-support.patch no longer
applies due to 4b74ebf726d444ba820830cad986a1f92f724649. After
resolving issues manually, it does not compile, because
4b74ebf726d444ba820830cad986a1f92f724649 also removes
save_userid/save_sec_context fields from ExecCreateTableAs.

>   if (RelationIsIVM(matviewRel) && stmt->skipData)
Now this function accepts skipData param.

5) For DISTINCT support patch uses hidden __ivm* columns. Is this
design discussed anywhere? I wonder if this is a necessity (only
solution) or if there are alternatives.
6)
What are the caveats of supporting some simple cases for aggregation
funcs like in example?
```
regress=# CREATE INCREMENTAL MATERIALIZED VIEW mv_ivm_2 AS SELECT
sum(j) + sum(i) from mv_base_a;
ERROR:  expression containing an aggregate in it is not supported on
incrementally maintainable materialized view
```
I can see some difficulties with division CREATE IMMV .... AS SELECT
1/sum(i) from mv_base_a;  (sum(i) == 0 case), but adding &
multiplication should be ok, aren't they?


Overall, patchset looks mature, however it is far from being
committable due to lack of testing/feedback/discussion. There is only
one way to fix this... Test and discuss it!


[1] https://github.com/cloudberrydb/cloudberrydb