Subject: [PATCH] Fix pg_dump emitting OVERRIDING SYSTEM VALUE for tables with dropped identity columns

From: William Bernbaum <[email-masked]>
Date: Fri, 17 Apr 2026 23:29:05 +0000

Hey hackers,

I've encountered a small issue in pg_dump.

It currently emits OVERRIDING SYSTEM VALUE in INSERTs for
a table that doesn't have an identity column if it used to have
a GENERATED ALWAYS AS IDENTITY column that was later dropped.

Simple repro:

    CREATE TABLE demo (
        id   BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
        fk_a BIGINT NOT NULL,
        fk_b BIGINT NOT NULL
    );

    INSERT INTO demo (fk_a, fk_b)
        OVERRIDING SYSTEM VALUE VALUES (1, 2);

    ALTER TABLE demo DROP COLUMN id;
    ALTER TABLE demo ADD PRIMARY KEY (fk_a, fk_b);

    pg_dump --data-only --inserts --table=demo mydb

Expected:

    INSERT INTO public.demo VALUES (1, 2);

Actual:

    INSERT INTO public.demo OVERRIDING SYSTEM VALUE VALUES (1, 2);

The clause is harmless, but it's misleading and causes noisy diffs.

In CI setups that rely on deterministic dumps, this can add significant friction
to reviews. We currently work around it by first clearing the stale markers:

UPDATE pg_catalog.pg_attribute a
   SET attidentity = ''
 FROM pg_catalog.pg_class c
  JOIN pg_catalog.pg_namespace n
    ON n.oid = c.relnamespace
WHERE a.attrelid = c.oid
   AND a.attisdropped
   AND a.attidentity <> ''
   AND n.nspname = 'public'
   AND c.relkind IN ('r', 'p');

Background:

After DROP COLUMN, the pg_attribute row is marked attisdropped = true,
but attidentity still has its old value ('a').

getTableAttrs() loops over all attributes (attnum > 0), including dropped
attributes, and does:

    tbinfo->needs_override = tbinfo->needs_override ||
        (tbinfo->attidentity[j] == ATTRIBUTE_IDENTITY_ALWAYS);

So a dropped column with attidentity = 'a' still flips needs_override to true,
and dumpTableData_insert() then always emits OVERRIDING SYSTEM VALUE
for the table.

The attached patch fixes this by ignoring dropped columns when setting
needs_override (i.e., checking !attisdropped).

I also considered clearing attidentity in DROP COLUMN, but that wouldn't
address the problem for already-stale catalog entries.

This seems to have been around since identity columns were added.

Patch attached.

Thoughts?

---

From: Andreas Karlsson <[email-masked]>
Date: Fri, 1 May 2026 09:28:28 +0200

On 4/18/26 01:29, William Bernbaum wrote:
> Hey hackers,
> 
> I’ve encountered a small issue in pg_dump.
> 
> [...]

Nicely spotted and thanks for the patch! Please add it to the currently 
open commitfest (https://commitfest.postgresql.org/59/) so it is not lost.

I have two pieces of feedback:

1. I think the code would be easier to read as

if (!tbinfo->attisdropped[j])
     tbinfo->needs_override = tbinfo->needs_override || 
tbinfo->attidentity[j] == ATTRIBUTE_IDENTITY_ALWAYS;

or even

if (tbinfo->attidentity[j] == ATTRIBUTE_IDENTITY_ALWAYS && 
!tbinfo->attisdropped[j])
     tbinfo->needs_override = true;

since then we do not get such a long line.

2. While I am not personally a fan of that file it would be more 
consistent if the new test was added as part of 002_pg_dump.pl if 
possible. Plus then it would mean that we would not need to create and 
tear down a PostgreSQL cluster.

Andreas

---

From: Andreas Karlsson <[email-masked]>
Date: Fri, 1 May 2026 09:39:07 +0200

> On 4/18/26 01:29, William Bernbaum wrote:

Forgot this: Maybe it is just a bit too early in the morning and I have 
not had coffee yet but I struggled a bit to apply your patch. A 
recommendation for making patches easy to apply for other developers is 
to generate them with the "git format-patch" command which makes them 
easy to apply with "git am". You can use the "-v" flag to "git 
format-patch" if you want to add a version number to the generated file 
names.
Also another question worth looking into is if this same bug affects 
other things, e.g. the setting of hasdefaults.

Thanks again for the patch!

--
Andreas Karlsson
Percona