Allow excluding folder names when scanning for dangling indices (#34349)

ES is scanning for dangling indices on every cluster state update. For this, it lists the subfolders of
the indices directory to determine which extra index directories exist on the node where there's no
corresponding index in the cluster state. These are potential targets for dangling index import. On
certain machine types, and with large number of indices, this subfolder listing can be horribly slow.
This means that every cluster state update will be slowed down by potentially hundreds of
milliseconds. One of the reasons for this poor performance is that Files.isDirectory() is a relatively
expensive call on some OS and JDK versions. There is no need though to do all these isDirectory
calls for folders which we know we are going to discard anyhow in the next step of the dangling
indices logic. This commit allows adding an exclusion predicate to the availableIndexFolders
methods which can dramatically speed up this method when scanning for dangling indices.

benchmarks/src/main/java/org/elasticsearch/benchmark/fs/AvailableIndexFoldersBenchmark.java

@@ -0,0 +1,94 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.benchmark.fs;
+
+import org.elasticsearch.common.logging.LogConfigurator;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.env.Environment;
+import org.elasticsearch.env.NodeEnvironment;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
+@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
+@Fork(3)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+public class AvailableIndexFoldersBenchmark {
+
+    private NodeEnvironment.NodePath nodePath;
+    private NodeEnvironment nodeEnv;
+    private Set<String> excludedDirs;
+
+    @Setup
+    public void setup() throws IOException {
+        Path path = Files.createTempDirectory("test");
+        String[] paths = new String[] {path.toString()};
+        nodePath = new NodeEnvironment.NodePath(path);
+
+        LogConfigurator.setNodeName("test");
+        Settings settings = Settings.builder()
+            .put(Environment.PATH_HOME_SETTING.getKey(), path)
+            .putList(Environment.PATH_DATA_SETTING.getKey(), paths).build();
+        nodeEnv = new NodeEnvironment(settings, new Environment(settings, null));
+
+        Files.createDirectories(nodePath.indicesPath);
+        excludedDirs = new HashSet<>();
+        int numIndices = 5000;
+        for (int i = 0; i < numIndices; i++) {
+            String dirName = "dir" + i;
+            Files.createDirectory(nodePath.indicesPath.resolve(dirName));
+            excludedDirs.add(dirName);
+        }
+        if (nodeEnv.availableIndexFoldersForPath(nodePath).size() != numIndices) {
+            throw new IllegalStateException("bad size");
+        }
+        if (nodeEnv.availableIndexFoldersForPath(nodePath, excludedDirs::contains).size() != 0) {
+            throw new IllegalStateException("bad size");
+        }
+    }
+
+
+    @Benchmark
+    public Set<String> availableIndexFolderNaive() throws IOException {
+        return nodeEnv.availableIndexFoldersForPath(nodePath);
+    }
+
+    @Benchmark
+    public Set<String> availableIndexFolderOptimized() throws IOException {
+        return nodeEnv.availableIndexFoldersForPath(nodePath, excludedDirs::contains);
+    }
+
+}

server/src/main/java/org/elasticsearch/env/NodeEnvironment.java

@@ -82,6 +82,7 @@ import java.util.concurrent.Semaphore;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Predicate;
 
 import static java.util.Collections.unmodifiableSet;
 
@@ -818,13 +819,21 @@ public final class NodeEnvironment  implements Closeable {
      * Returns all folder names in ${data.paths}/nodes/{node.id}/indices folder
      */
     public Set<String> availableIndexFolders() throws IOException {
+        return availableIndexFolders(p -> false);
+    }
+
+    /**
+     * Returns folder names in ${data.paths}/nodes/{node.id}/indices folder that don't match the given predicate.
+     * @param excludeIndexPathIdsPredicate folder names to exclude
+     */
+    public Set<String> availableIndexFolders(Predicate<String> excludeIndexPathIdsPredicate) throws IOException {
         if (nodePaths == null || locks == null) {
             throw new IllegalStateException("node is not configured to store local location");
         }
         assertEnvIsLocked();
         Set<String> indexFolders = new HashSet<>();
         for (NodePath nodePath : nodePaths) {
-            indexFolders.addAll(availableIndexFoldersForPath(nodePath));
+            indexFolders.addAll(availableIndexFoldersForPath(nodePath, excludeIndexPathIdsPredicate));
         }
         return indexFolders;
 
@@ -838,6 +847,19 @@ public final class NodeEnvironment  implements Closeable {
      * @throws IOException if an I/O exception occurs traversing the filesystem
      */
     public Set<String> availableIndexFoldersForPath(final NodePath nodePath) throws IOException {
+        return availableIndexFoldersForPath(nodePath, p -> false);
+    }
+
+    /**
+     * Return directory names in the nodes/{node.id}/indices directory for the given node path that don't match the given predicate.
+     *
+     * @param nodePath the path
+     * @param excludeIndexPathIdsPredicate folder names to exclude
+     * @return all directories that could be indices for the given node path.
+     * @throws IOException if an I/O exception occurs traversing the filesystem
+     */
+    public Set<String> availableIndexFoldersForPath(final NodePath nodePath, Predicate<String> excludeIndexPathIdsPredicate)
+        throws IOException {
         if (nodePaths == null || locks == null) {
             throw new IllegalStateException("node is not configured to store local location");
         }
@@ -847,8 +869,9 @@ public final class NodeEnvironment  implements Closeable {
         if (Files.isDirectory(indicesLocation)) {
             try (DirectoryStream<Path> stream = Files.newDirectoryStream(indicesLocation)) {
                 for (Path index : stream) {
-                    if (Files.isDirectory(index)) {
-                        indexFolders.add(index.getFileName().toString());
+                    final String fileName = index.getFileName().toString();
+                    if (excludeIndexPathIdsPredicate.test(fileName) == false && Files.isDirectory(index)) {
+                        indexFolders.add(fileName);
                     }
                 }
             }

server/src/main/java/org/elasticsearch/gateway/MetaStateService.java

@@ -85,10 +85,9 @@ public class MetaStateService extends AbstractComponent {
      */
     List<IndexMetaData> loadIndicesStates(Predicate<String> excludeIndexPathIdsPredicate) throws IOException {
         List<IndexMetaData> indexMetaDataList = new ArrayList<>();
-        for (String indexFolderName : nodeEnv.availableIndexFolders()) {
-            if (excludeIndexPathIdsPredicate.test(indexFolderName)) {
-                continue;
-            }
+        for (String indexFolderName : nodeEnv.availableIndexFolders(excludeIndexPathIdsPredicate)) {
+            assert excludeIndexPathIdsPredicate.test(indexFolderName) == false :
+                "unexpected folder " + indexFolderName + " which should have been excluded";
             IndexMetaData indexMetaData = IndexMetaData.FORMAT.loadLatestState(logger, namedXContentRegistry,
                 nodeEnv.resolveIndexFolder(indexFolderName));
             if (indexMetaData != null) {

server/src/test/java/org/elasticsearch/env/NodeEnvironmentTests.java

@@ -19,6 +19,7 @@
 package org.elasticsearch.env;
 
 import org.apache.lucene.index.SegmentInfos;
+import org.elasticsearch.common.util.set.Sets;
 import org.elasticsearch.core.internal.io.IOUtils;
 import org.apache.lucene.util.LuceneTestCase;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
@@ -186,6 +187,27 @@ public class NodeEnvironmentTests extends ESTestCase {
         env.close();
     }
 
+    public void testAvailableIndexFoldersWithExclusions() throws Exception {
+        final NodeEnvironment env = newNodeEnvironment();
+        final int numIndices = randomIntBetween(1, 10);
+        Set<String> excludedPaths = new HashSet<>();
+        Set<String> actualPaths = new HashSet<>();
+        for (int i = 0; i < numIndices; i++) {
+            Index index = new Index("foo" + i, "fooUUID" + i);
+            for (Path path : env.indexPaths(index)) {
+                Files.createDirectories(path.resolve(MetaDataStateFormat.STATE_DIR_NAME));
+                actualPaths.add(path.getFileName().toString());
+            }
+            if (randomBoolean()) {
+                excludedPaths.add(env.indexPaths(index)[0].getFileName().toString());
+            }
+        }
+
+        assertThat(Sets.difference(actualPaths, excludedPaths), equalTo(env.availableIndexFolders(excludedPaths::contains)));
+        assertTrue("LockedShards: " + env.lockedShards(), env.lockedShards().isEmpty());
+        env.close();
+    }
+
     public void testResolveIndexFolders() throws Exception {
         final NodeEnvironment env = newNodeEnvironment();
         final int numIndices = randomIntBetween(1, 10);