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Re: Pgoutput not capturing the generated columns

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Shubham Khanna <khannashubham1197@gmail.com>, Peter Smith <smithpb2250@gmail.com>, vignesh C <vignesh21@gmail.com>, Rajendra Kumar Dangwal <dangwalrajendra888@gmail.com>, pgsql-hackers@lists.postgresql.org, euler@eulerto.com
Date: 2024-10-22T10:50:00Z
Lists: pgsql-hackers 
On Wed, Oct 9, 2024 at 10:19 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> Regarding the 0001 patch, it seems to me that UPDATE and DELETE are
> allowed on the table even if its replica identity is set to generated
> columns that are not published. For example, consider the following
> scenario:
>
> create table t (a int not null, b int generated always as (a + 1)
> stored not null);
> create unique index t_idx on t (b);
> alter table t replica identity using index t_idx;
> create publication pub for table t with (publish_generated_columns = false);
> insert into t values (1);
> update t set a = 100 where a = 1;
>
> The publication pub doesn't include the generated column 'b' which is
> the replica identity of the table 't'. Therefore, the update message
> generated by the last UPDATE would have NULL for the column 'b'. I
> think we should not allow UPDATE and DELETE on such a table.
>

I see the same behavior even without a patch on the HEAD. See the
following example executed on HEAD:

postgres=# create table t (a int not null, b int generated always as (a + 1)
postgres(# stored not null);
CREATE TABLE
postgres=# create unique index t_idx on t (b);
CREATE INDEX
postgres=# alter table t replica identity using index t_idx;
ALTER TABLE
postgres=# create publication pub for table t;
CREATE PUBLICATION
postgres=# insert into t values (1);
INSERT 0 1
postgres=# update t set a = 100 where a = 1;
UPDATE 1

So, the update is allowed even when we don't publish generated
columns, if so, why do we need to handle it in this patch when the
user gave publish_generated_columns=false?

Also, on the subscriber side, I see the ERROR: "publisher did not send
replica identity column expected by the logical replication target
relation "public.t"".

Considering this, I feel if find this behavior buggy then we should
fix this separately rather than part of this patch. What do you think?

-- 
With Regards,
Amit Kapila.

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Doc: Generated column replication.

  2. Rename pubgencols_type to pubgencols in pg_publication.

  3. Doc: Fix column name in pg_publication catalog.

  4. Fix buildfarm failure introduced by commit e65dbc9927.

  5. Change publication's publish_generated_columns option type to enum.

  6. Fix \dRp+ output when describing publications with a lower server version.

  7. Replicate generated columns when 'publish_generated_columns' is set.

  8. Doc: Update the behavior of generated columns in Logical Replication.

  9. Replicate generated columns when specified in the column list.

  10. Doc: Generated columns are skipped for logical replication.