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Subject: Re: show size of DSAs and dshash tables in
 pg_dsm_registry_allocations
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: <aS20Z42rPHecTljS@nathan>
Date: Tue, 2 Dec 2025 05:35:34 +0800
Cc: Rahila Syed <rahilasyed90@gmail.com>,
 Robert Haas <robertmhaas@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <E4CEC5F7-BCCE-47D7-B206-48FD31F06F3C@gmail.com>
References: <aSeEDeznAsHR1_YF@nathan>
 <CAH2L28tr5q965MbD2TroyTc-Ey+b-z3=3kpWAuGg6w7qQwwChA@mail.gmail.com>
 <aS20Z42rPHecTljS@nathan>
To: Nathan Bossart <nathandbossart@gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/E4CEC5F7-BCCE-47D7-B206-48FD31F06F3C%40gmail.com>
Precedence: bulk

Hi Nathan,

V2 overall looks good to me. I just got a question and a few nit =
comments.

> On Dec 1, 2025, at 23:29, Nathan Bossart <nathandbossart@gmail.com> =
wrote:
>=20
> --=20
> nathan
> <v2-0001-rework-DSM-registry-view.patch>

1 - dsa.c
```
+size_t
+dsa_get_total_size_from_handle(dsa_handle handle)
+{
+	size_t		size;
+	bool		already_attached;
+	dsm_segment *segment;
+	dsa_area_control *control;
+
+	already_attached =3D dsa_is_attached(handle);
+	if (already_attached)
+		segment =3D dsm_find_mapping(handle);
+	else
+		segment =3D dsm_attach(handle);
+
+	if (segment =3D=3D NULL)
+		ereport(ERROR,
+				=
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("could not attach to dynamic =
shared area")));
```

Why do you error out instead of reporting 0/NULL usage here? When users =
call this function as shown in the test script:
```
CREATE VIEW pg_dsm_registry_allocations AS
SELECT * FROM pg_get_dsm_registry_allocations();
```

User doesn=E2=80=99t pass in a handle, if the DSA has been released, it =
should treat a missing mapping as =E2=80=9Cno size available=E2=80=9D =
and maybe return NULL.=20


2
```
+		else if (entry->type =3D=3D DSMR_ENTRY_TYPE_DSH &&
+				 entry->dsh.dsa_handle =
!=3DDSA_HANDLE_INVALID)
```

Missing a white space after !=3D.

3
```
-       Size of the allocation in bytes.  NULL for entries of type
-       <literal>area</literal> and <literal>hash</literal>.
+       Size of the allocation in bytes.  NULL for entries that failed
+       initialization.
```

=E2=80=9CFailed initialization=E2=80=9D, I guess =E2=80=9Cto=E2=80=9D is =
needed after =E2=80=9Cfailed=E2=80=9D.

4
```
-SELECT name, type, size IS DISTINCT FROM 0 AS size
+SELECT name, type, size > 0 AS size
```

As you changed the third column from =E2=80=9Csize=E2=80=9D to =E2=80=9Csi=
ze > 0=E2=80=9D, now it=E2=80=99s a bool column, so maybe rename the =
column alias from =E2=80=9Csize=E2=80=9D to something indicating a bool =
type, such as =E2=80=9Csize_ok=E2=80=9D, =E2=80=9Chas_size=E2=80=9D, =
etc.


Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/