fix_GetWalAvailability.patch

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 700271fd40..199053dd4a 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -11240,18 +11240,25 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
        <itemizedlist>
         <listitem>
          <para><literal>normal</literal> means that the claimed files
-          are within <varname>max_wal_size</varname>.</para>
+          are within <varname>max_wal_size</varname>. If
+          <varname>max_slot_wal_keep_size</varname> is smaller than
+          <varname>max_wal_size</varname>, this state will not appear.</para>
         </listitem>
         <listitem>
          <para><literal>reserved</literal> means
           that <varname>max_wal_size</varname> is exceeded but the files are
           still held, either by some replication slot or
-          by <varname>wal_keep_segments</varname>.</para>
+          by <varname>wal_keep_segments</varname>.
+          </para>
         </listitem>
         <listitem>
-         <para><literal>lost</literal> means that some WAL files are
-          definitely lost and this slot cannot be used to resume replication
-          anymore.</para>
+          <para>
+            <literal>lost</literal> means that some required WAL files are
+			removed and this slot is no longer usable after once disconnected
+			during this state. Note that there are cases where the state moves
+			back to reserved or normal state when all wal senders have left
+			the just removed segment before being terminated.
+          </para>
         </listitem>
        </itemizedlist>
        The last two states are seen only when
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 55cac186dc..d1501d0cf7 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9528,8 +9528,8 @@ GetWALAvailability(XLogRecPtr targetLSN)
 
 	/* calculate oldest segment by max_wal_size and wal_keep_segments */
 	XLByteToSeg(currpos, currSeg, wal_segment_size);
-	keepSegs = ConvertToXSegs(Max(max_wal_size_mb, wal_keep_segments),
-							  wal_segment_size) + 1;
+	keepSegs = Max(ConvertToXSegs(max_wal_size_mb, wal_keep_segments),
+				   wal_segment_size) + 1;
 
 	if (currSeg > keepSegs)
 		oldestSegMaxWalSize = currSeg - keepSegs;