Document hazards of --slot.

diff --git a/doc/src/sgml/ref/pg_receivexlog.sgml b/doc/src/sgml/ref/pg_receivexlog.sgml
index e592699ac766cb2c35be7b3771d228f86d176252..2a44af46c529784335192b62fc0c5a8585f25770 100644 (file)
--- a/doc/src/sgml/ref/pg_receivexlog.sgml
+++ b/doc/src/sgml/ref/pg_receivexlog.sgml
@@ -232,6 +232,14 @@ PostgreSQL documentation
         <para>
          Require <application>pg_receivexlog</application> to use an existing
          replication slot (see <xref linkend="streaming-replication-slots">).
+         When this option is used, <application>pg_receivexlog</> will report
+         a flush position to the server, indicating when each segment has been
+         synchronized to disk so that the server can remove that segment if it
+         is not otherwise needed.  When using this paramter, it is important
+         to make sure that <application>pg_receivexlog</> cannot become the
+         synchronous standby through an incautious setting of
+         <xref linkend="guc-synchronous-standby-names">; it does not flush
+         data frequently enough for this to work correctly.
         </para>
       </listitem>
      </varlistentry>