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Subject: Re: doc: Improve wal_level and effective_wal_level GUC around logical
 replication
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: 
 <CAKFQuwY=WLF0OH8JE5T8S=aj0LBydiSn02fkRE73Sm_KSLRqJQ@mail.gmail.com>
Date: Wed, 8 Apr 2026 10:40:10 +0800
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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Message-Id: <33F33315-9A7D-41A2-9F37-0A361E5A4C7F@gmail.com>
References: 
 <CAKFQuwY=WLF0OH8JE5T8S=aj0LBydiSn02fkRE73Sm_KSLRqJQ@mail.gmail.com>
To: "David G. Johnston" <david.g.johnston@gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/33F33315-9A7D-41A2-9F37-0A361E5A4C7F%40gmail.com>
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> On Mar 4, 2026, at 23:55, David G. Johnston =
<david.g.johnston@gmail.com> wrote:
>=20
> Hi,
>=20
> In evaluating the proposed change to wal_level docs in [1] I found it =
to be undesirable, but the discussion and my own review discovered some =
other changes that should be considered.
>=20
> Since effective_wal_level now exists, Logical Replication Getting =
Started needs to be updated.
> Add links to the main topics that the different levels apply to.
> Be explicit about the ordering of minimal, replica, and logical.
> Move the behavior of effective_wal_level to the GUC for it, leaving =
behind just the pointer that wal_level is now just a "minimum".
>=20
> David J.
>=20
> [1] =
https://www.postgresql.org/message-id/CA%2Bv5N42vKtY17653eBHFx%2BCw06E2fSm=
PrXmX2qKYG23%3D4Ycd7A%40mail.gmail.com
> <v1-0001-doc-Add-some-clarity-around-wal_level.patch>


A few comments:

1
```
--- a/doc/src/sgml/logical-replication.sgml
+++ b/doc/src/sgml/logical-replication.sgml
@@ -3508,11 +3508,12 @@ pg_ctl -D /opt/PostgreSQL/data2_upgraded start =
-l logfile
   <title>Quick Setup</title>
=20
   <para>
-   First set the configuration options in =
<filename>postgresql.conf</filename>:
+   Ensure that <xref linkend=3D"guc-effective-wal-level"/> is at least =
replica
+   (this is the default).
 <programlisting>
-wal_level =3D logical
+SHOW effective_wal_level;
 </programlisting>
-   The other required settings have default values that are sufficient =
for a
+   The other required settings also have default values that are =
sufficient for a
    basic setup.
   </para>
```

I think wal_level should be at least =E2=80=9Clogical=E2=80=9D. I =
don=E2=80=99t get why did you change to =E2=80=9Creplica=E2=80=9D? =
It=E2=80=99s clear that we still need =E2=80=9Clogical=E2=80=9D to =
support logical replication.

2
```
+        <literal>replica</literal>, which writes enough data to support
+        WAL archiving (see <xref linkend=3D"continuous-archiving"/>) =
and
+        physical replication (see <xref =
linkend=3D"streaming-replication"/>)
+        Running read-only queries on a standby server. Below that is =
<literal>minimal</literal>,
```

Here, =E2=80=9CRunning read-only =E2=80=A6=E2=80=9D sentence looks not =
smooth, and there is not a period for the last sentence before =
=E2=80=9CRunning". The old wording was =E2=80=9Cincluding running =
read-only =E2=80=A6.=E2=80=9D.

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