Improve log compaction efficiency/correctness in AtomixDocumentTree.

Change-Id: I48305d38236c8f773928de1874b21ecc57a7a7de
diff --git a/core/store/primitives/src/main/java/org/onosproject/store/primitives/resources/impl/AtomixDocumentTreeCommands.java b/core/store/primitives/src/main/java/org/onosproject/store/primitives/resources/impl/AtomixDocumentTreeCommands.java
index 9921b88..153dbcb 100644
--- a/core/store/primitives/src/main/java/org/onosproject/store/primitives/resources/impl/AtomixDocumentTreeCommands.java
+++ b/core/store/primitives/src/main/java/org/onosproject/store/primitives/resources/impl/AtomixDocumentTreeCommands.java
@@ -187,6 +187,11 @@
         }
 
         @Override
+        public CompactionMode compaction() {
+            return value == null ? CompactionMode.TOMBSTONE : CompactionMode.QUORUM;
+        }
+
+        @Override
         public String toString() {
             return MoreObjects.toStringHelper(getClass())
                     .add("path", path())
@@ -209,6 +214,11 @@
         @Override
         public void readObject(BufferInput<?> buffer, Serializer serializer) {
         }
+
+        @Override
+        public CompactionMode compaction() {
+            return CompactionMode.TOMBSTONE;
+        }
     }
 
     /**
@@ -226,6 +236,11 @@
         }
 
         @Override
+        public CompactionMode compaction() {
+            return CompactionMode.QUORUM;
+        }
+
+        @Override
         public String toString() {
             return MoreObjects.toStringHelper(getClass())
                     .add("path", path())
@@ -248,6 +263,11 @@
         }
 
         @Override
+        public CompactionMode compaction() {
+            return CompactionMode.TOMBSTONE;
+        }
+
+        @Override
         public String toString() {
             return MoreObjects.toStringHelper(getClass())
                     .add("path", path())