Add CHANGES and release note for #1775

CHANGES

+5473.	[func]		The rbt hashtable implementation has been changed
+			to use faster hash-function (HalfSipHash2-4) and
+			uses Fibonacci hashing for better distribution.
+			Setting the max-cache-size now preallocates fixed
+			size hashtable, so the rehashing doesn't cause
+			resolution brownouts when growing the hashtable.
+			[GL #1775]
+
 5472.	[func]		The statistics channel has been updated to use the
 			new network manager. [GL #2022]
 

doc/notes/notes-current.rst

@@ -39,7 +39,12 @@ New Features
 Feature Changes
 ~~~~~~~~~~~~~~~
 
-- None.
+- BIND's cache database implementation has been updated to use a faster
+  hash-function with better distribution.  In addition, the effective
+  max-cache-size (configured explicitly, defaulting to a value based on system
+  memory or set to 'unlimited') now pre-allocates fixed size hash tables. This
+  prevents interruption to query resolution when the hash tables need to be
+  increased in size. [GL #1775]
 
 Bug Fixes
 ~~~~~~~~~