Reword alpha release note item on SSI.

Per Josh Berkus; some additional explanatory text by me.

diff --git a/doc/src/sgml/release-9.1.sgml b/doc/src/sgml/release-9.1.sgml
index be8d65ae4be9408746420282fd7d69d6f0159169..6682106820c1e1f34a19d50a36b0ef3567d44552 100644 (file)
--- a/doc/src/sgml/release-9.1.sgml
+++ b/doc/src/sgml/release-9.1.sgml
@@ -196,7 +196,14 @@
 
        
         
-         Implement a truly serializable isolation level
+         Implement Serializable Snapshot Isolation, in order to
+         provide a more robust serializable transaction mode.
+        
+        
+         In previous releases, the REPEATABLE READ and SERIALIZABLE isolation
+         levels were identical.  The historical behavior of REPEATABLE READ is
+         unchanged in this release, but SERIALIZABLE now provides stronger
+         guarantees.