Add a release note about the more aggressive reclamation of deleted documents.
The fact that Elasticsearch 6.5 will be based on Lucene 7.5 means that it will
benefit from improvements to merging, in particular more aggressive reclamation
of deleted documents.
@@ -78,9 +78,17 @@ location of the hosts file has moved from
// [[feature-6.5.0]]
// === New Features
-// [float]
-// [[enhancement-6.5.0]]
-// === Enhancements
+[float]
+[[enhancement-6.5.0]]
+=== Enhancements
+
+Merging::
+* The default merge policy (`tiered`) used to allow up to 50% of deleted
+documents per shard, possibly more in the case of a
+<<indices-forcemerge,force-merged index>>. This threshold is now 33%, meaning
+that deleted documents may only make an index up to about 50% larger than the
+same index without deleted document, versus 2x previously. Also this threshold
+now also applies to indices that have been force-merged in the past.
// [float]
// [[bug-6.5.0]]
