diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 074afee..e02b94d 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4290,7 +4290,8 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
        executing command for each active session, for the
        <structname>pg_stat_activity</>.<structfield>query</> field.
        The default value is 1024. This parameter can only be set at server
-       start.
+       start and will also not take effect until any pre-existing statistics
+       are cleared.
        </para>
       </listitem>
      </varlistentry>