From bbffd871a28cf2c7b4dc9ba92f9e3ab7e246e3c5 Mon Sep 17 00:00:00 2001
From: Jason Tedor <jason@tedor.me>
Date: Mon, 16 Jan 2017 08:04:02 -0500
Subject: [PATCH] Clarify handling of version conflict

This commit adds a comment explaining why version conflicts during
recovery and on replicas are considered normal and thus why we return a
successful result.
---
 .../java/org/elasticsearch/index/engine/InternalEngine.java   | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/core/src/main/java/org/elasticsearch/index/engine/InternalEngine.java b/core/src/main/java/org/elasticsearch/index/engine/InternalEngine.java
index 72daca9b8f54f..d024c876f47c7 100644
--- a/core/src/main/java/org/elasticsearch/index/engine/InternalEngine.java
+++ b/core/src/main/java/org/elasticsearch/index/engine/InternalEngine.java
@@ -487,6 +487,10 @@ private <T extends Result> Optional<T> checkVersionConflict(
                         op.versionType().explainConflictForWrites(currentVersion, expectedVersion, deleted));
                 result = onFailure.apply(e);
             } else {
+                /*
+                 * Version conflicts during recovery and on replicas are normal due to asynchronous execution; as such, we should return a
+                 * successful result.
+                 */
                 result = onSuccess.get();
             }
             return Optional.of(result);