From fc3a69b6fa82c9f6ecdc11b0885d34a39f5e5884 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Thu, 11 Jan 2018 15:00:32 +0900
Subject: [PATCH 4/4] Documentation for slot-limit feature

---
 doc/src/sgml/catalogs.sgml          | 28 ++++++++++++++++++++++++++++
 doc/src/sgml/config.sgml            | 23 +++++++++++++++++++++++
 doc/src/sgml/high-availability.sgml |  8 +++++---
 3 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 9edba96fab..fc4cbc9239 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -9881,6 +9881,34 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
       </entry>
      </row>

+     <row>
+      <entry><structfield>wal_status</structfield></entry>
+      <entry><type>text</type></entry>
+      <entry></entry>
+
+      <entry>Availability of WAL records claimed by the
+      slot. <literal>streaming</literal>, <literal>keeping</literal>,
+      <literal>lost</literal>
+      or <literal>unknown</literal>. <literal>streaming</literal> means that
+      the claimed records are available. <literal>keeping</literal> means that
+      some of them are to be removed by the next checkpoint.
+      <literal>lost</literal> means that some of them are no longer
+      available. The last two states are seen only when
+      <xref linkend="guc-max-slot-wal-keep-size"/> is non-negative. If the
+      slot doesn't have valid restart_lsn, this field
+      is <literal>unknown</literal>.
+      </entry>
+     </row>
+
+     <row>
+      <entry><structfield>remain</structfield></entry>
+      <entry><type>bigint</type></entry>
+      <entry></entry>
+      <entry>The amount in bytes that WAL location (LSN) can advance until the
+        slot may lose required WAL records.
+      </entry>
+     </row>
+
     </tbody>
    </tgroup>
   </table>
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 7554cba3f9..f3e504862c 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3117,6 +3117,29 @@ include_dir 'conf.d'
        </listitem>
       </varlistentry>

+      <varlistentry id="guc-max-slot-wal-keep-size" xreflabel="max_slot_wal_keep_size">
+       <term><varname>max_slot_wal_keep_size</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_slot_wal_keep_size</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+       <para>
+        Specify the maximum size of WAL files
+        that <link linkend="streaming-replication-slots">replication
+        slots</link> are allowed to retain in the <filename>pg_wal</filename>
+        directory at checkpoint time.
+        If <varname>max_slot_wal_keep_size</varname> is -1 (the default),
+        replication slots retain unlimited size of WAL files.  If restart_lsn
+        of a replication slot gets behind more than that bytes from the
+        current LSN, the standby using the slot may no longer be able to
+        reconnect due to removal of required WAL records. You can see the WAL
+        availability of replication slots
+        in <link linkend="view-pg-replication-slots">pg_replication_slots</link>.
+       </para>
+       </listitem>
+      </varlistentry>
+
      <varlistentry id="guc-wal-sender-timeout" xreflabel="wal_sender_timeout">
       <term><varname>wal_sender_timeout</varname> (<type>integer</type>)
       <indexterm>
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index ebcb3daaed..15a98340a6 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -927,9 +927,11 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass'
     <xref linkend="guc-archive-command"/>.
     However, these methods often result in retaining more WAL segments than
     required, whereas replication slots retain only the number of segments
-    known to be needed.  An advantage of these methods is that they bound
-    the space requirement for <literal>pg_wal</literal>; there is currently no way
-    to do this using replication slots.
+    known to be needed.  On the other hand, replication slots can retain so
+    many WAL segments that they fill up the space allotted
+    for <literal>pg_wal</literal>;
+    <xref linkend="guc-max-slot-wal-keep-size"/> limits the size of WAL files
+    retained by replication slots.
    </para>
    <para>
     Similarly, <xref linkend="guc-hot-standby-feedback"/>
-- 
2.16.3