docs: PG 12 relnotes, update btree items

Reported-by: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-Wzn-aH4ToZEWR05ELSSp7bO_JMn=sMPfUhNruwVmCXKh-w@mail.gmail.com

diff --git a/doc/src/sgml/release-12.sgml b/doc/src/sgml/release-12.sgml
index 4a6c989f3f064cd2c1855bb46f04963f71217f4a..fcc49ffcf9ada0d7075f6394896ab51807d009f4 100644 (file)
--- a/doc/src/sgml/release-12.sgml
+++ b/doc/src/sgml/release-12.sgml
@@ -606,22 +606,64 @@ Author: Tom Lane 
 
       
 
 
        
-        Improve speed of btree index insertions (Peter Geoghegan,
-        Alexander Korotkov)
+        Improve performance and space utilization of btree indexes with
+        many duplicates (Peter Geoghegan, Heikki Linnakangas)
+       
+
+       
+        Previously, duplicate index entries were stored unordered within
+        their duplicate groups.  This caused overhead during index
+        inserts, wasted space due to excessive page splits, and reduced
+        VACUUM's ability to recycle entire pages.
+        Duplicate index entries are now sorted in heap-storage order.
+       
+
+       
+        Indexes pg_upgraded from previous
+        releases will not have these benefits.
+       
+      
+
+      
+
+
+       
+        Allow multi-column btree indexes to be smaller (Peter Geoghegan,
+        Heikki Linnakangas)
+       
+
+       
+        Internal pages and min/max leaf page indicators now only store
+        index keys until the change key, rather than all indexed keys.
+        This also improves the locality of index access.
        
 
        
-        The new code improves the space-efficiency of page splits,
-        reduces locking overhead, and gives better performance for
-        UPDATEs and DELETEs on
-        indexes with many duplicates.
+        Indexes pg_upgraded from previous
+        releases will not have these benefits.
+       
+      
+
+      
+
+
+       
+        Improve speed of btree index insertions by reducing locking
+        overhead (Alexander Korotkov)
        
       
 
@@ -680,25 +722,6 @@ Author: Tom Lane 
 
       
 
-
-       
-        Have new btree indexes sort duplicate index entries in heap-storage
-        order (Peter Geoghegan, Heikki Linnakangas)
-       
-
-       
-        Indexes pg_upgraded from previous
-        releases will not have this ordering.
-       
-      
-
-      
-