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From: Chao Li <[email protected]>
To: David G. Johnston <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: doc: Improve wal_level and effective_wal_level GUC around logical replication
Date: Wed, 8 Apr 2026 10:40:10 +0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAKFQuwY=WLF0OH8JE5T8S=aj0LBydiSn02fkRE73Sm_KSLRqJQ@mail.gmail.com>
References: <CAKFQuwY=WLF0OH8JE5T8S=aj0LBydiSn02fkRE73Sm_KSLRqJQ@mail.gmail.com>



> On Mar 4, 2026, at 23:55, David G. Johnston <[email protected]> wrote:
> 
> Hi,
> 
> 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.
> 
> 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".
> 
> David J.
> 
> [1] https://www.postgresql.org/message-id/CA%2Bv5N42vKtY17653eBHFx%2BCw06E2fSmPrXmX2qKYG23%3D4Ycd7A%40ma...
> <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>
 
   <para>
-   First set the configuration options in <filename>postgresql.conf</filename>:
+   Ensure that <xref linkend="guc-effective-wal-level"/> is at least replica
+   (this is the default).
 <programlisting>
-wal_level = 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 “logical”. I don’t get why did you change to “replica”? It’s clear that we still need “logical” to support logical replication.

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

Here, “Running read-only …” sentence looks not smooth, and there is not a period for the last sentence before “Running". The old wording was “including running read-only ….”.

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

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