Fix Index Deletion during Snapshot Finalization

server/src/main/java/org/elasticsearch/snapshots/SnapshotsService.java

@@ -1510,7 +1510,7 @@ private static ImmutableOpenMap<ShardId, SnapshotsInProgress.ShardSnapshotStatus
     }
 
     /**
-     * Returns the indices that are currently being snapshotted (with partial == false) and that are contained in the indices-to-check set.
+     * Returns the indices that are currently being snapshotted and that are contained in the indices-to-check set.
      */
     public static Set<Index> snapshottingIndices(final ClusterState currentState, final Set<Index> indicesToCheck) {
         final SnapshotsInProgress snapshots = currentState.custom(SnapshotsInProgress.TYPE);
@@ -1521,21 +1521,10 @@ public static Set<Index> snapshottingIndices(final ClusterState currentState, fi
         final Set<Index> indices = new HashSet<>();
         for (final SnapshotsInProgress.Entry entry : snapshots.entries()) {
             if (entry.partial() == false) {
-                if (entry.state() == State.INIT) {
-                    for (IndexId index : entry.indices()) {
-                        IndexMetaData indexMetaData = currentState.metaData().index(index.getName());
-                        if (indexMetaData != null && indicesToCheck.contains(indexMetaData.getIndex())) {
-                            indices.add(indexMetaData.getIndex());
-                        }
-                    }
-                } else {
-                    for (ObjectObjectCursor<ShardId, SnapshotsInProgress.ShardSnapshotStatus> shard : entry.shards()) {
-                        Index index = shard.key.getIndex();
-                        if (indicesToCheck.contains(index)
-                            && shard.value.state().completed() == false
-                            && currentState.getMetaData().index(index) != null) {
-                            indices.add(index);
-                        }
+                for (IndexId index : entry.indices()) {
+                    IndexMetaData indexMetaData = currentState.metaData().index(index.getName());
+                    if (indexMetaData != null && indicesToCheck.contains(indexMetaData.getIndex())) {
+                        indices.add(indexMetaData.getIndex());
                     }
                 }
             }

server/src/test/java/org/elasticsearch/snapshots/SnapshotResiliencyTests.java

@@ -80,6 +80,7 @@
 import org.elasticsearch.action.support.ActiveShardCount;
 import org.elasticsearch.action.support.AutoCreateIndex;
 import org.elasticsearch.action.support.DestructiveOperations;
+import org.elasticsearch.action.support.GroupedActionListener;
 import org.elasticsearch.action.support.PlainActionFuture;
 import org.elasticsearch.action.support.TransportAction;
 import org.elasticsearch.action.support.WriteRequest;
@@ -502,6 +503,50 @@ public void testConcurrentSnapshotCreateAndDeleteOther() {
         }
     }
 
+    public void testConcurrentSnapshotDeleteAndDeleteIndex() {
+        setupTestCluster(randomFrom(1, 3, 5), randomIntBetween(2, 10));
+
+        String repoName = "repo";
+        String snapshotName = "snapshot";
+        final String index = "test";
+
+        TestClusterNodes.TestClusterNode masterNode =
+            testClusterNodes.currentMaster(testClusterNodes.nodes.values().iterator().next().clusterService.state());
+
+        final StepListener<Collection<CreateIndexResponse>> createIndicesListener = new StepListener<>();
+
+        continueOrDie(createRepoAndIndex(repoName, index, 1), createIndexResponse -> {
+            // create a few more indices to make it more likely that the subsequent index delete operation happens before snapshot
+            // finalization
+            final int indices = randomIntBetween(5, 20);
+            final GroupedActionListener<CreateIndexResponse> listener = new GroupedActionListener<>(createIndicesListener, indices);
+            for (int i = 0; i < indices; ++i) {
+                client().admin().indices().create(new CreateIndexRequest("index-" + i), listener);
+            }
+        });
+
+        final StepListener<CreateSnapshotResponse> createSnapshotResponseStepListener = new StepListener<>();
+
+        continueOrDie(createIndicesListener, createIndexResponses ->
+            client().admin().cluster().prepareCreateSnapshot(repoName, snapshotName).setWaitForCompletion(false)
+                .execute(createSnapshotResponseStepListener));
+
+        continueOrDie(createSnapshotResponseStepListener,
+            createSnapshotResponse -> client().admin().indices().delete(new DeleteIndexRequest(index), noopListener()));
+
+        deterministicTaskQueue.runAllRunnableTasks();
+
+        SnapshotsInProgress finalSnapshotsInProgress = masterNode.clusterService.state().custom(SnapshotsInProgress.TYPE);
+        assertFalse(finalSnapshotsInProgress.entries().stream().anyMatch(entry -> entry.state().completed() == false));
+        final Repository repository = masterNode.repositoriesService.repository(repoName);
+        Collection<SnapshotId> snapshotIds = getRepositoryData(repository).getSnapshotIds();
+        assertThat(snapshotIds, hasSize(1));
+
+        final SnapshotInfo snapshotInfo = repository.getSnapshotInfo(snapshotIds.iterator().next());
+        assertEquals(SnapshotState.SUCCESS, snapshotInfo.state());
+        assertEquals(0, snapshotInfo.failedShards());
+    }
+
     /**
      * Simulates concurrent restarts of data and master nodes as well as relocating a primary shard, while starting and subsequently
      * deleting a snapshot.