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%40mail.gmail.com
From f4f229b4f16cfb674950e08f213dc64d854c980d Mon Sep 17 00:00:00 2001 From: "David G. Johnston" <[email protected]> Date: Wed, 4 Mar 2026 08:04:42 -0700 Subject: [PATCH v1] doc: Add some clarity around wal_level --- doc/src/sgml/config.sgml | 51 ++++++++++++--------------- doc/src/sgml/logical-replication.sgml | 7 ++-- 2 files changed, 27 insertions(+), 31 deletions(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index f670e2d4c31..406518aae63 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -3072,15 +3072,21 @@ include_dir 'conf.d' </term> <listitem> <para> - <varname>wal_level</varname> determines how much information is written to - the WAL. The default value is <literal>replica</literal>, which writes enough - data to support WAL archiving and replication, including running - read-only queries on a standby server. <literal>minimal</literal> removes all - logging except the information required to recover from a crash or - immediate shutdown. Finally, - <literal>logical</literal> adds information necessary to support logical - decoding. Each level includes the information logged at all lower - levels. This parameter can only be set at server start. + <varname>wal_level</varname> determines the minimum amount of information + that is to be written to the WAL. The default, and middle, value is + <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>, + which removes all logging except the information required to recover from a crash or + immediate shutdown. Finally, above replica, is <literal>logical</literal>, + which adds information necessary to support logical decoding and + logical replication (see <xref linkend="logical-replication"/>). + Each level includes the information logged at all lower levels. + The <xref linkend="guc-effective-wal-level"/> parameter reports the actual + level used by the system. Namely, whether replica has been promoted to + logical (minimal never promotes). + This parameter can only be set at server start. </para> <para> The <literal>minimal</literal> level generates the least WAL @@ -3117,17 +3123,6 @@ include_dir 'conf.d' many <command>UPDATE</command> and <command>DELETE</command> statements are executed. </para> - <para> - It is important to note that when <varname>wal_level</varname> is set to - <literal>replica</literal>, the effective WAL level can automatically change - based on the presence of <link linkend="logicaldecoding-replication-slots"> - logical replication slots</link>. The system automatically increases the - effective WAL level to <literal>logical</literal> when creating the first - logical replication slot, and decreases it back to <literal>replica</literal> - when dropping or invalidating the last logical replication slot. The current - effective WAL level can be monitored through - <xref linkend="guc-effective-wal-level"/> parameter. - </para> <para> In releases prior to 9.6, this parameter also allowed the values <literal>archive</literal> and <literal>hot_standby</literal>. @@ -11945,17 +11940,17 @@ dynamic_library_path = '/usr/local/lib/postgresql:$libdir' system. This parameter shares the same set of values as <xref linkend="guc-wal-level"/>, but reflects the operational WAL level rather than the configured setting. For descriptions of - possible values, refer to the <varname>wal_level</varname> + possible values, refer to the <xref linkend="guc-wal-level"/> parameter documentation. </para> <para> - The effective WAL level can differ from the configured - <varname>wal_level</varname> in certain situations. For example, - when <varname>wal_level</varname> is set to <literal>replica</literal> - and the system has one or more logical replication slots, - <varname>effective_wal_level</varname> will show <literal>logical</literal> - to indicate that the system is maintaining WAL records at - <literal>logical</literal> level equivalent. + Presently, on primary servers, differences from <xref linkend="guc-wal-level"/> + only happen when <xref linkend="guc-wal-level"/> is set to <literal>replica</literal>. + Based on the presence of <link linkend="logicaldecoding-replication-slots"> + logical replication slots</link>, the system automatically increases the + effective WAL level to <literal>logical</literal> when creating the first + logical replication slot, and decreases it back to <literal>replica</literal> + when dropping or invalidating the last logical replication slot. </para> <para> On standby servers, <varname>effective_wal_level</varname> matches diff --git a/doc/src/sgml/logical-replication.sgml b/doc/src/sgml/logical-replication.sgml index 5028fe9af09..c709224de0a 100644 --- 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> -- 2.43.0
