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From: Kirill Reshke <reshkekirill@gmail.com>
Date: Tue, 30 Jul 2024 03:32:19 +0500
Message-ID: <CALdSSPip9ruUoQMmsD_hQ0xY72qB=_jB-ayHeUWUH-dd0MB60A@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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On Sat, 27 Jul 2024 at 13:26, Kirill Reshke <reshkekirill@gmail.com> wrote:
>
> 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

Hi! Small update: I tried to run a regression test and all
IMMV-related tests failed on my vm. Maybe I'm doing something wrong, I
will try to investigate.

Another suggestion: support for \d and \d+ commands in psql. With v34
patchset applied, psql does not show anything IMMV-related in \d mode.

```
reshke=# \d m1
           Materialized view "public.m1"
 Column |  Type   | Collation | Nullable | Default
--------+---------+-----------+----------+---------
 i      | integer |           |          |
Distributed by: (i)


reshke=# \d+ m1
                                     Materialized view "public.m1"
 Column |  Type   | Collation | Nullable | Default | Storage |
Compression | Stats target | Description
--------+---------+-----------+----------+---------+---------+-------------+--------------+-------------
 i      | integer |           |          |         | plain   |
    |              |
View definition:
 SELECT t1.i
   FROM t1;
Distributed by: (i)
Access method: heap

```

Output should be 'Incrementally materialized view "public.m1"' IMO.