Use the smallest version rather than the default version

The minimum version comparison was always using the default version
sicne the comparison was flipped.

Closes #11474

src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -23,8 +23,6 @@
 import com.google.common.base.Preconditions;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.index.CheckIndex;
-import org.apache.lucene.search.Query;
-import org.apache.lucene.search.join.BitDocIdSetFilter;
 import org.apache.lucene.store.AlreadyClosedException;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.ThreadInterruptedException;
@@ -41,14 +39,11 @@
 import org.elasticsearch.cluster.routing.ShardRoutingState;
 import org.elasticsearch.common.Booleans;
 import org.elasticsearch.common.Nullable;
-import org.elasticsearch.common.Strings;
-import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.logging.ESLogger;
 import org.elasticsearch.common.lucene.Lucene;
-import org.elasticsearch.common.lucene.search.Queries;
 import org.elasticsearch.common.metrics.MeanMetric;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.ByteSizeValue;
@@ -720,13 +715,13 @@ public org.apache.lucene.util.Version upgrade(UpgradeRequest upgrade) {
     }
 
     public org.apache.lucene.util.Version minimumCompatibleVersion() {
-        org.apache.lucene.util.Version luceneVersion = Version.LUCENE_3_EMULATION_VERSION;
+        org.apache.lucene.util.Version luceneVersion = null;
         for(Segment segment : engine().segments(false)) {
-            if (luceneVersion.onOrAfter(segment.getVersion())) {
+            if (luceneVersion == null || luceneVersion.onOrAfter(segment.getVersion())) {
                 luceneVersion = segment.getVersion();
             }
         }
-        return luceneVersion;
+        return luceneVersion == null ?  Version.indexCreated(indexSettings).luceneVersion : luceneVersion;
     }
 
     public SnapshotIndexCommit snapshotIndex(boolean flushFirst) throws EngineException {

src/test/java/org/elasticsearch/index/shard/IndexShardTests.java

@@ -50,6 +50,7 @@
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_REPLICAS;
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_SHARDS;
 import static org.elasticsearch.common.settings.Settings.settingsBuilder;
+import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_VERSION_CREATED;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertNoFailures;
 import static org.hamcrest.Matchers.equalTo;
@@ -362,4 +363,19 @@ public void testDeleteByQueryBWC() {
             assertEquals(numDocs, searcher.reader().numDocs());
         }
     }
+
+    public void testMinimumCompatVersion() {
+        Version versionCreated = VersionUtils.randomVersion(random());
+        assertAcked(client().admin().indices().prepareCreate("test")
+                .setSettings(SETTING_NUMBER_OF_SHARDS, 1, SETTING_NUMBER_OF_REPLICAS, 0, SETTING_VERSION_CREATED, versionCreated.id));
+        client().prepareIndex("test", "test").setSource("{}").get();
+        ensureGreen("test");
+        IndicesService indicesService = getInstanceFromNode(IndicesService.class);
+        IndexShard test = indicesService.indexService("test").shard(0);
+        assertEquals(versionCreated.luceneVersion, test.minimumCompatibleVersion());
+        client().prepareIndex("test", "test").setSource("{}").get();
+        assertEquals(versionCreated.luceneVersion, test.minimumCompatibleVersion());
+        test.engine().flush();
+        assertEquals(Version.CURRENT.luceneVersion, test.minimumCompatibleVersion());
+    }
 }

src/test/java/org/elasticsearch/rest/action/admin/indices/upgrade/UpgradeReallyOldIndexTest.java

@@ -19,7 +19,11 @@
 
 package org.elasticsearch.rest.action.admin.indices.upgrade;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.bwcompat.StaticIndexBackwardCompatibilityTest;
+import org.elasticsearch.cluster.metadata.IndexMetaData;
+import org.elasticsearch.index.IndexService;
+import org.elasticsearch.indices.IndicesService;
 
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertNoFailures;
 
@@ -29,13 +33,26 @@ public void testUpgrade_0_90_6() throws Exception {
         String indexName = "index-0.90.6";
 
         loadIndex(indexName);
+        assertMinVersion(indexName, org.apache.lucene.util.Version.parse("4.5.1"));
         UpgradeTest.assertNotUpgraded(client(), indexName);
         assertTrue(UpgradeTest.hasAncientSegments(client(), indexName));
         assertNoFailures(client().admin().indices().prepareUpgrade(indexName).setUpgradeOnlyAncientSegments(true).get());
 
         assertFalse(UpgradeTest.hasAncientSegments(client(), "index-0.90.6"));
         // This index has only ancient segments, so it should now be fully upgraded:
         UpgradeTest.assertUpgraded(client(), indexName);
+        assertEquals(Version.CURRENT.luceneVersion.toString(), client().admin().indices().prepareGetSettings(indexName).get().getSetting(indexName, IndexMetaData.SETTING_VERSION_MINIMUM_COMPATIBLE));
+        assertMinVersion(indexName, Version.CURRENT.luceneVersion);
+    }
+
+    private void assertMinVersion(String index, org.apache.lucene.util.Version version) {
+        for (IndicesService services : internalCluster().getInstances(IndicesService.class)) {
+            IndexService indexService = services.indexService(index);
+            if (indexService != null) {
+                assertEquals(version, indexService.shard(0).minimumCompatibleVersion());
+            }
+        }
+
     }
 
 }