diff --git a/doc/src/sgml/biblio.sgml b/doc/src/sgml/biblio.sgml
index b40c06eb38..e72a65ff8a 100644
--- a/doc/src/sgml/biblio.sgml
+++ b/doc/src/sgml/biblio.sgml
@@ -230,6 +230,64 @@ ssimkovi@ag.or.at
   <bibliodiv>
    <title>Proceedings and Articles</title>
 
+   <biblioentry id="ports12">
+    <biblioset relation="article">
+     <title><ulink url="https://arxiv.org/pdf/1208.4179">Serializable Snapshot Isolation in PostgreSQL</ulink></title>
+     <authorgroup>
+      <author>
+       <firstname>D.</firstname>
+       <surname>Ports</surname>
+      </author>
+      <author>
+       <firstname>K.</firstname>
+       <surname>Grittner</surname>
+      </author>
+     </authorgroup>
+    </biblioset>
+    <confgroup>
+     <conftitle>VLDB Conference</conftitle>
+     <confdates>August 2012</confdates>
+     <address>Istanbul, Turkey</address>
+    </confgroup>
+   </biblioentry>
+
+   <biblioentry id="berenson95">
+    <biblioset relation="article">
+     <title><ulink url="https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/tr-95-51.pdf">A Critique of ANSI SQL Isolation Levels</ulink></title>
+     <authorgroup>
+      <author>
+       <firstname>H.</firstname>
+       <surname>Berenson</surname>
+      </author>
+      <author>
+       <firstname>P.</firstname>
+       <surname>Bernstein</surname>
+      </author>
+      <author>
+       <firstname>J.</firstname>
+       <surname>Gray</surname>
+      </author>
+      <author>
+       <firstname>J.</firstname>
+       <surname>Melton</surname>
+      </author>
+      <author>
+       <firstname>E.</firstname>
+       <surname>O'Neil</surname>
+      </author>
+      <author>
+       <firstname>P.</firstname>
+       <surname>O'Neil</surname>
+      </author>
+     </authorgroup>
+    </biblioset>
+    <confgroup>
+     <conftitle>ACM-SIGMOD Conference on Management of Data</conftitle>
+     <confdates>June 1995</confdates>
+     <address>San Jose, California</address>
+    </confgroup>
+   </biblioentry>
+
    <biblioentry id="olson93">
     <title>Partial indexing in POSTGRES: research project</title>
     <authorgroup>
diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index a826f2b4e4..dda6f1f2ad 100644
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -535,6 +535,20 @@ ERROR:  could not serialize access due to concurrent update
     of explicit locks to block conflicting transactions.
    </para>
 
+   <para>
+    The Repeatable Read isolation level is implemented using a technique
+    known in academic database literature and in some other database products
+    as <firstterm>Snapshot Isolation</firstterm>.  Differences in behavior
+    and performance may be observed when compared with systems that use a
+    traditional locking technique that reduces concurrency.  Some other
+    systems may even offer Repeatable Read and Snapshot Isolation as distinct
+    isolation levels with different behavior.  The permitted phenomena that
+    distinguish the two techniques were not formalized by database researchers
+    until after the SQL standard was developed, and are outside the scope of
+    this manual.  For a full treatment, please see
+    <xref linkend="berenson95"/>.
+   </para>
+
    <note>
     <para>
      Prior to <productname>PostgreSQL</productname> version 9.1, a request
@@ -783,6 +797,15 @@ ERROR:  could not serialize access due to read/write dependencies among transact
      </listitem>
     </itemizedlist>
    </para>
+
+   <para>
+    The Serializable isolation level is implemented using a technique known
+    in academic database literature as Serializable Snapshot Isolation, which
+    builds on Snapshot Isolation by adding checks for serialization anomalies.
+    Some differences in behavior and performance may be observed when compared
+    with other systems that use a traditional locking technique.  Please see
+    <xref linkend="ports12"/> for detailed information.
+   </para>
   </sect2>
  </sect1>
 
@@ -1726,6 +1749,16 @@ SELECT pg_advisory_lock(q.id) FROM
     see a transient state that is inconsistent with any serial execution
     of the transactions on the master.
    </para>
+
+   <para>
+    Internal access to the system catalogs is not done using the isolation
+    level of the current transaction.  This means that newly created database
+    objects such as tables are visible to concurrent Repeatable Read and
+    Serializable transactions, even though the rows they contain are not.  In
+    contrast, queries that explicitly examine the system catalogs don't see
+    rows representing concurrently created database objects, in the higher
+    isolation levels.
+   </para>
   </sect1>
 
   <sect1 id="locking-indexes">