doc: improve wal_level docs for the 'minimal' level

Reported-by: David G. Johnston
Discussion: https://postgr.es/m/CAKFQuwZ24UcfkoyLLSW3PMGQATomOcw1nuYFRuMev-NoOF+mYw@mail.gmail.com

Author: David G. Johnston

Backpatch-through: 14, partial to 13

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 37fd80388c0e602fe7d01a8208b04df84b551cd4..c2bdacb6a78c645427406553e915566de0ad9cf5 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2764,9 +2764,10 @@ include_dir 'conf.d'
         levels.  This parameter can only be set at server start.
        
        
-        In minimal level, no information is logged for
-        permanent relations for the remainder of a transaction that creates or
-        rewrites them.  This can make operations much faster (see
+        The minimal level generates the least WAL
+        volume.  It logs no row information for permanent relations
+        in transactions that create or
+        rewrite them.  This can make operations much faster (see
         ).  Operations that initiate this
         optimization include:
         
@@ -2778,19 +2779,20 @@ include_dir 'conf.d'
          REINDEX
          TRUNCATE
         
-        But minimal WAL does not contain enough information to reconstruct the
-        data from a base backup and the WAL logs, so replica or
-        higher must be used to enable WAL archiving
-        () and streaming replication.
+        However, minimal WAL does not contain sufficient information for
+        point-in-time recovery, so replica or
+        higher must be used to enable continuous archiving
+        () and streaming binary replication.
+        In fact, the server will not even start in this mode if
+        max_wal_senders is non-zero.
         Note that changing wal_level to
-        minimal makes any base backups taken before
-        unavailable for archive recovery and standby server, which may
-        lead to data loss.
+        minimal makes previous base backups unusable
+        for point-in-time recovery and standby servers.
        
        
         In logical level, the same information is logged as
-        with replica, plus information needed to allow
-        extracting logical change sets from the WAL. Using a level of
+        with replica, plus information needed to
+        extract logical change sets from the WAL. Using a level of
         logical will increase the WAL volume, particularly if many
         tables are configured for REPLICA IDENTITY FULL and
         many UPDATE and DELETE statements are