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Subject: BUG #19739: Parameterized first autocommit statement can have
 different `transaction_timestamp()` and `statement
To: pgsql-bugs@lists.postgresql.org
From: PG Bug reporting form <noreply@postgresql.org>
Cc: theshallow27@gmail.com
Reply-To: theshallow27@gmail.com, pgsql-bugs@lists.postgresql.org
Date: Fri, 02 Oct 2026 22:37:31 +0000
Message-ID: <19739-bdca3e8fd9b496fa@postgresql.org>
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Archived-At: 
 <https://www.postgresql.org/message-id/19739-bdca3e8fd9b496fa%40postgresql.org>
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The following bug has been logged on the website:

Bug reference:      19739
Logged by:          Shallow
Email address:      theshallow27@gmail.com
PostgreSQL version: 18.6
Operating system:   Linux
Description:       =20

The documentation says `transaction_timestamp()` and
`statement_timestamp()` return the same value during the first statement of
a
transaction. With a parameterized query executed as the first command on a
fresh autocommit connection, they differ. The same query without parameters
returns equality. Parameterized execution uses the extended query protocol,
so
this may expose a distinction between Parse/Bind/Execute message timing and
the documented =E2=80=9Cfirst statement=E2=80=9D guarantee.

**Reproduction:** Using Psycopg with autocommit enabled on a fresh
connection:

```python
cur.execute(
    "SELECT transaction_timestamp() =3D statement_timestamp() WHERE %s::int=
 =3D
0",
    (0,),
)
print(cur.fetchone())  # (False,)
```

Control query on a fresh autocommit connection:

```sql
SELECT transaction_timestamp() =3D statement_timestamp(); -- true
```

**Expected result:** The parameterized query, as the first SQL statement in
an
implicit transaction, should return `true`; alternatively, the documentation
should clarify how extended-protocol messages affect the guarantee.