diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index d5c6076d4a..db820d6f43 100644
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -515,8 +515,9 @@ ERROR: could not serialize access due to concurrent update
- The Serializable isolation level provides the strictest transaction
- isolation. This level emulates serial transaction execution,
+ The Serializable isolation level provides
+ the strictest transaction isolation. This level emulates serial
+ transaction execution for all committed transactions;
as if transactions had been executed one after another, serially,
rather than concurrently. However, like the Repeatable Read level,
applications using this level must
@@ -571,6 +572,20 @@ ERROR: could not serialize access due to read/write dependencies among transact
computed by A.
+
+ When relying on Serializable transactions to prevent anomalies, it is
+ important that any data read from a permanent user table not be
+ considered valid until the transaction which read it has successfully
+ committed. This is true even for read-only transactions, except that
+ data read within a deferrable read-only
+ transaction is known to be valid as soon as it is read, because such a
+ transaction waits until it can acquire a snapshot guaranteed to be free
+ from such problems before starting to read any data. In all other cases
+ applications must not depend on results read during a transaction that
+ later aborted; instead, they should retry the transaction until it
+ succeeds.
+
+
To guarantee true serializability PostgreSQL
uses predicate locking>, which means that it keeps locks