[WHATSNEW] Add text about GUID index change

[Andrew Bartlett]

Sorry this was missed when this feature was done a few months back.

Please include in 4.8

Andrew Bartlett
-- 
Andrew Bartlett
https://samba.org/~abartlet/
Authentication Developer, Samba Team         https://samba.org
Samba Development and Support, Catalyst IT   
https://catalyst.net.nz/services/samba



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From c59157c0973b39d708e86470beeee4ae7f02e65f Mon Sep 17 00:00:00 2001
From: Andrew Bartlett <abartlet at samba.org>
Date: Thu, 22 Feb 2018 14:01:07 +1300
Subject: [PATCH] WHATSNEW: Explain implications of GUID index change

Signed-off-by: Andrew Bartlett <abartlet at samba.org>
---
 WHATSNEW.txt | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/WHATSNEW.txt b/WHATSNEW.txt
index 6b111c4cdd5..357a8f637d1 100644
--- a/WHATSNEW.txt
+++ b/WHATSNEW.txt
@@ -12,10 +12,32 @@ Samba 4.8 will be the next version of the Samba suite.
 UPGRADING
 =========
 
+New GUID Index mode in sam.ldb for the AD DC
+--------------------------------------------
+
+Users who upgrade a Samba AD DC in-place will experience a short delay
+in the first startup of Samba while the sam.ldb is re-indexed.
+
+Unlike in previous releases a transparent downgrade is not possible.
+If you wish to downgrade such a DB to a Samba 4.7 or earlier version,
+please run the source4/scripting/bin/sambaundoguididx script first.
 
 NEW FEATURES/CHANGES
 ====================
 
+New GUID Index mode in sam.ldb for the AD DC
+--------------------------------------------
+
+The new layout used for sam.ldb is GUID, rather than DN oriented.
+This provides Samba's Active Directory Domain Controller with a faster
+database, particularly at larger scale.
+
+The underlying DB is still TDB, simply the choice of key has changed.
+
+The new mode is not optional, so no configuration is required.  Older
+Samba versions cannot read the new database (see the upgrade
+note above).
+
 KDC GPO application
 -------------------
 
-- 
2.11.0