apply review comments

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataIndexUpgradeService.java

@@ -166,7 +166,7 @@ public class MetaDataIndexUpgradeService extends AbstractComponent {
 
     /**
      * Elasticsearch 3.0 no longer supports indices with pre Lucene v5.0 (Elasticsearch v2.0.0.beta1) segments. All indices
-     * that were created before Elasticsearch v2.0.0.beta1 should be upgraded using upgrade plugin before they can
+     * that were created before Elasticsearch v2.0.0.beta1 should be upgraded using upgrade API before they can
      * be open by this version of elasticsearch.
      */
     private void checkSupportedVersion(IndexMetaData indexMetaData) {
@@ -185,10 +185,6 @@ public class MetaDataIndexUpgradeService extends AbstractComponent {
             // The index was created with elasticsearch that was using Lucene 5.2.1
             return true;
         }
-        if (indexMetaData.getUpgradeVersion().onOrAfter(Version.V_2_0_0_beta1) == false) {
-            // early terminate if we are not upgrade - we don't even need to look at the segment version
-            return false;
-        }
         if (indexMetaData.getMinimumCompatibleVersion() != null &&
                 indexMetaData.getMinimumCompatibleVersion().onOrAfter(org.apache.lucene.util.Version.LUCENE_5_0_0)) {
             //The index was upgraded we can work with it

core/src/main/java/org/elasticsearch/index/engine/InternalEngine.java

@@ -172,21 +172,12 @@ public class InternalEngine extends Engine {
     }
 
     private Translog openTranslog(EngineConfig engineConfig, IndexWriter writer, boolean createNew) throws IOException {
-        final Translog.TranslogGeneration generation = loadTranslogIdFromCommit(writer);
+        final Translog.TranslogGeneration generation = loadTranslogIdFromCommit(writer, createNew);
         final TranslogConfig translogConfig = engineConfig.getTranslogConfig();
-
+        translogConfig.setTranslogGeneration(generation);
-        if (createNew == false) {
-            // We expect that this shard already exists, so it must already have an existing translog else something is badly wrong!
-            if (generation == null) {
-                throw new IllegalStateException("no translog generation present in commit data but translog is expected to exist");
-            }
-            translogConfig.setTranslogGeneration(generation);
-            if (generation != null && generation.translogUUID == null) {
-                throw new IndexFormatTooOldException("trasnlog", "translog has no generation nor a UUID - this might be an index from a previous version consider upgrading to N-1 first");
-            }
-        }
         final Translog translog = new Translog(translogConfig);
         if (generation == null || generation.translogUUID == null) {
+            assert createNew;
             if (generation == null) {
                 logger.debug("no translog ID present in the current generation - creating one");
             } else if (generation.translogUUID == null) {
@@ -249,7 +240,7 @@ public class InternalEngine extends Engine {
      * translog id into lucene and returns null.
      */
     @Nullable
-    private Translog.TranslogGeneration loadTranslogIdFromCommit(IndexWriter writer) throws IOException {
+    private Translog.TranslogGeneration loadTranslogIdFromCommit(IndexWriter writer, boolean createNew) throws IOException {
         // commit on a just opened writer will commit even if there are no changes done to it
         // we rely on that for the commit data translog id key
         final Map<String, String> commitUserData = writer.getCommitData();
@@ -262,8 +253,16 @@ public class InternalEngine extends Engine {
             }
             final String translogUUID = commitUserData.get(Translog.TRANSLOG_UUID_KEY);
             final long translogGen = Long.parseLong(commitUserData.get(Translog.TRANSLOG_GENERATION_KEY));
+            if (createNew == false &&  translogUUID == null) {
+                throw new IndexFormatTooOldException("translog", "translog has no generation nor a UUID - this might be an index from a previous version consider upgrading to N-1 first");
+            }
             return new Translog.TranslogGeneration(translogUUID, translogGen);
         }
+
+        if (createNew == false) {
+            // We expect that this shard already exists, so it must already have an existing translog else something is badly wrong!
+            throw new IllegalStateException("no translog generation present in commit data but translog is expected to exist");
+        }
         return null;
     }
 

core/src/test/java/org/elasticsearch/ExceptionSerializationTests.java

@@ -705,7 +705,7 @@ public class ExceptionSerializationTests extends ESTestCase {
         ids.put(61, org.elasticsearch.cluster.routing.RoutingValidationException.class);
         ids.put(62, org.elasticsearch.common.io.stream.NotSerializableExceptionWrapper.class);
         ids.put(63, org.elasticsearch.indices.AliasFilterParsingException.class);
-        ids.put(64, org.elasticsearch.index.engine.DeleteByQueryFailedEngineException.class);
+        ids.put(64, null); // DeleteByQueryFailedEngineException was removed in 3.0
         ids.put(65, org.elasticsearch.gateway.GatewayException.class);
         ids.put(66, org.elasticsearch.index.shard.IndexShardNotRecoveringException.class);
         ids.put(67, org.elasticsearch.http.HttpException.class);