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RE: Pgoutput not capturing the generated columns

Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com>

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From: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
To: 'vignesh C' <vignesh21@gmail.com>
Cc: Shubham Khanna <khannashubham1197@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Rajendra Kumar Dangwal <dangwalrajendra888@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Peter Smith <smithpb2250@gmail.com>, "euler@eulerto.com" <euler@eulerto.com>
Date: 2024-11-01T07:57:03Z
Lists: pgsql-hackers 
Dear Vignesh,

Thanks for rebasing the patch! Before reviewing deeply, I want to confirm the specification.
I understood like below based on the documentation.

- If publish_generated_columns is false, the publication won't replicate generated columns
- If publish_generated_columns is true, the behavior on the subscriber depends on the table column:
  - If it is a generated column even on the subscriber, it causes an ERROR.
  - If it is a regular column, the generated value is replicated.
  - If the column is missing, it causes an ERROR.

However, below test implies that generated columns can be replicated even if
publish_generated_columns is false. Not sure...

```
# Verify that incremental replication of generated columns occurs
# when they are included in the column list, regardless of the
# publish_generated_columns option.
$result =
  $node_subscriber->safe_psql('postgres', "SELECT * FROM tab3 ORDER BY a");
is( $result, qq(|2
|4
|6
|8),
	'tab3 incremental replication, when publish_generated_columns=false');
```

Also, I've tested the case both pub and sub had the generated column, but the ERROR was strange for me.

```
test_pub=# CREATE TABLE gencoltable (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
test_pub=# CREATE PUBLICATION pub FOR TABLE gencoltable(a, b) WITH (publish_generated_columns = true);
test_pub=# INSERT INTO gencoltable (a) VALUES (generate_series(1, 10));

test_sub=# CREATE TABLE gencoltable (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
test_sub=# CREATE SUBSCRIPTION sub CONNECTION ... PUBLICATION pub;

-> ERROR: logical replication target relation "public.gencoltable" is missing replicated column: "b"
```

The attribute existed on the sub but it was reported as missing column. I think
we should somehow report like "generated column on publisher is replicated the
generated column on the subscriber".

Best regards,
Hayato Kuroda
FUJITSU LIMITED

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.