From 87ef072436f327228e132c2547c8c94c2f2150e7 Mon Sep 17 00:00:00 2001
From: Robert Varga <rovarga@cisco.com>
Date: Sun, 21 Dec 2014 01:53:08 +0100
Subject: [PATCH] BUG-2350: improve performance of data tree merges

Profiling has revealed that performing a merge on a large subtree
results in all pre-existing nodes being verified. The MD-SAL performs an
empty merge whenever the user asks for parents to be created --
resulting in up to 75% overhead.

Change-Id: I94310b2cb27c8585a8b8c4933ff0f0f658fda9be
Signed-off-by: Robert Varga <rovarga@cisco.com>
---
 .../yang/data/impl/schema/tree/ModifiedNode.java | 13 +++++++++++++
 .../schema/tree/OperationWithModification.java   | 16 ++++++++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/schema/tree/ModifiedNode.java b/yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/schema/tree/ModifiedNode.java
index ecda366de0..bc6b46d46f 100644
--- a/yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/schema/tree/ModifiedNode.java
+++ b/yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/schema/tree/ModifiedNode.java
@@ -270,6 +270,19 @@ final class ModifiedNode implements StoreTreeNode<ModifiedNode>, Identifiable<Pa
                 + modificationType + ", childModification=" + children + "]";
     }
 
+    /**
+     * Create a node which will reflect the state of this node, except it will behave as newly-written
+     * value. This is useful only for merge validation.
+     *
+     * @param value Value associated with the node
+     * @return An isolated node. This node should never reach a datatree.
+     */
+    ModifiedNode asNewlyWritten(final NormalizedNode<?, ?> value) {
+        final ModifiedNode ret = new ModifiedNode(getIdentifier(), Optional.<TreeNode>absent(), false);
+        ret.write(value);
+        return ret;
+    }
+
     public static ModifiedNode createUnmodified(final TreeNode metadataTree, final boolean isOrdered) {
         return new ModifiedNode(metadataTree.getIdentifier(), Optional.of(metadataTree), isOrdered);
     }
diff --git a/yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/schema/tree/OperationWithModification.java b/yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/schema/tree/OperationWithModification.java
index bcf2101ff0..3293a05b06 100644
--- a/yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/schema/tree/OperationWithModification.java
+++ b/yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/schema/tree/OperationWithModification.java
@@ -31,13 +31,13 @@ final class OperationWithModification {
         applyOperation.verifyStructure(modification);
     }
 
-    private void mergeImpl(final NormalizedNode<?,?> data) {
+    private void recursiveMerge(final NormalizedNode<?,?> data) {
         if (data instanceof NormalizedNodeContainer<?,?,?>) {
             @SuppressWarnings({ "rawtypes", "unchecked" })
             NormalizedNodeContainer<?,?,NormalizedNode<PathArgument, ?>> dataContainer = (NormalizedNodeContainer) data;
             for (NormalizedNode<PathArgument, ?> child : dataContainer.getValue()) {
                 PathArgument childId = child.getIdentifier();
-                forChild(childId).mergeImpl(child);
+                forChild(childId).recursiveMerge(child);
             }
         }
 
@@ -45,8 +45,16 @@ final class OperationWithModification {
     }
 
     void merge(final NormalizedNode<?, ?> data) {
-        mergeImpl(data);
-        applyOperation.verifyStructure(modification);
+        /*
+         * A merge operation will end up overwriting parts of the tree, retaining others.
+         * We want to make sure we do not validate the complete resulting structure, but
+         * rather just what was written. In order to do that, we first pretend the data
+         * was written, run verification and then perform the merge -- with the explicit
+         * assumption that adding the newly-validated data with the previously-validated
+         * data will not result in invalid data.
+         */
+        applyOperation.verifyStructure(modification.asNewlyWritten(data));
+        recursiveMerge(data);
     }
 
     void delete() {
-- 
2.36.6