[RCI] Add NoOpEngine for closed indices (#33903)

This commit adds a new NoOpEngine implementation based on the current 
ReadOnlyEngine. This new implementation uses an empty DirectoryReader 
with no segments readers and will always returns 0 docs. The NoOpEngine 
is the default Engine created for IndexShards of closed indices. It expects 
an empty translog when it is instantiated.

Relates to #33888

server/src/main/java/org/elasticsearch/index/engine/NoOpEngine.java

@@ -0,0 +1,149 @@
+/*
+ * 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.index.engine;
+
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexCommit;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.LeafReader;
+import org.apache.lucene.store.Directory;
+import org.elasticsearch.common.Nullable;
+import org.elasticsearch.core.internal.io.IOUtils;
+import org.elasticsearch.index.translog.Translog;
+import org.elasticsearch.index.translog.TranslogConfig;
+import org.elasticsearch.index.translog.TranslogCorruptedException;
+import org.elasticsearch.index.translog.TranslogDeletionPolicy;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+import java.util.function.LongSupplier;
+import java.util.stream.Stream;
+
+/**
+ * NoOpEngine is an engine implementation that does nothing but the bare minimum
+ * required in order to have an engine. All attempts to do something (search,
+ * index, get), throw {@link UnsupportedOperationException}. This does maintain
+ * a translog with a deletion policy so that when flushing, no translog is
+ * retained on disk (setting a retention size and age of 0).
+ *
+ * It's also important to notice that this does list the commits of the Store's
+ * Directory so that the last commit's user data can be read for the historyUUID
+ * and last committed segment info.
+ */
+public final class NoOpEngine extends ReadOnlyEngine {
+
+    public NoOpEngine(EngineConfig engineConfig) {
+        super(engineConfig, null, null, true, directoryReader -> directoryReader);
+        boolean success = false;
+        try {
+            // The deletion policy for the translog should not keep any translogs around, so the min age/size is set to -1
+            final TranslogDeletionPolicy translogDeletionPolicy = new TranslogDeletionPolicy(-1, -1);
+
+            // The translog is opened and closed to validate that the translog UUID from lucene is the same as the one in the translog
+            try (Translog translog = openTranslog(engineConfig, translogDeletionPolicy, engineConfig.getGlobalCheckpointSupplier())) {
+                final int nbOperations = translog.totalOperations();
+                if (nbOperations != 0) {
+                    throw new IllegalArgumentException("Expected 0 translog operations but there were " + nbOperations);
+                }
+            }
+            success = true;
+        } catch (IOException | TranslogCorruptedException e) {
+            throw new EngineCreationFailureException(shardId, "failed to create engine", e);
+        } finally {
+            if (success == false) {
+                IOUtils.closeWhileHandlingException(this);
+            }
+        }
+    }
+
+    @Override
+    protected DirectoryReader open(final Directory directory) throws IOException {
+        final List<IndexCommit> indexCommits = DirectoryReader.listCommits(directory);
+        assert indexCommits.size() == 1 : "expected only one commit point";
+        IndexCommit indexCommit = indexCommits.get(indexCommits.size() - 1);
+        return new DirectoryReader(directory, new LeafReader[0]) {
+            @Override
+            protected DirectoryReader doOpenIfChanged() throws IOException {
+                return null;
+            }
+
+            @Override
+            protected DirectoryReader doOpenIfChanged(IndexCommit commit) throws IOException {
+                return null;
+            }
+
+            @Override
+            protected DirectoryReader doOpenIfChanged(IndexWriter writer, boolean applyAllDeletes) throws IOException {
+                return null;
+            }
+
+            @Override
+            public long getVersion() {
+                return 0;
+            }
+
+            @Override
+            public boolean isCurrent() throws IOException {
+                return true;
+            }
+
+            @Override
+            public IndexCommit getIndexCommit() throws IOException {
+                return indexCommit;
+            }
+
+            @Override
+            protected void doClose() throws IOException {
+            }
+
+            @Override
+            public CacheHelper getReaderCacheHelper() {
+                return null;
+            }
+        };
+    }
+
+    private Translog openTranslog(EngineConfig engineConfig, TranslogDeletionPolicy translogDeletionPolicy,
+                                  LongSupplier globalCheckpointSupplier) throws IOException {
+        final TranslogConfig translogConfig = engineConfig.getTranslogConfig();
+        final String translogUUID = loadTranslogUUIDFromLastCommit();
+        // We expect that this shard already exists, so it must already have an existing translog else something is badly wrong!
+        return new Translog(translogConfig, translogUUID, translogDeletionPolicy, globalCheckpointSupplier,
+                engineConfig.getPrimaryTermSupplier());
+    }
+
+    /**
+     * Reads the current stored translog ID from the last commit data.
+     */
+    @Nullable
+    private String loadTranslogUUIDFromLastCommit() {
+        final Map<String, String> commitUserData = getLastCommittedSegmentInfos().getUserData();
+        if (commitUserData.containsKey(Translog.TRANSLOG_GENERATION_KEY) == false) {
+            throw new IllegalStateException("Commit doesn't contain translog generation id");
+        }
+        return commitUserData.get(Translog.TRANSLOG_UUID_KEY);
+    }
+
+    @Override
+    public boolean ensureTranslogSynced(Stream<Translog.Location> locations) {
+        throw new UnsupportedOperationException("Translog synchronization should never be needed");
+    }
+}

server/src/main/java/org/elasticsearch/indices/IndicesService.java

@@ -84,6 +84,7 @@
 import org.elasticsearch.index.engine.CommitStats;
 import org.elasticsearch.index.engine.EngineFactory;
 import org.elasticsearch.index.engine.InternalEngineFactory;
+import org.elasticsearch.index.engine.NoOpEngine;
 import org.elasticsearch.index.fielddata.IndexFieldDataCache;
 import org.elasticsearch.index.flush.FlushStats;
 import org.elasticsearch.index.get.GetStats;
@@ -532,6 +533,12 @@ private synchronized IndexService createIndexService(final String reason,
     }
 
     private EngineFactory getEngineFactory(final IndexSettings idxSettings) {
+        final IndexMetaData indexMetaData = idxSettings.getIndexMetaData();
+        if (indexMetaData != null && indexMetaData.getState() == IndexMetaData.State.CLOSE) {
+            // NoOpEngine takes precedence as long as the index is closed
+            return NoOpEngine::new;
+        }
+
         final List<Optional<EngineFactory>> engineFactories =
                 engineFactoryProviders
                         .stream()

server/src/test/java/org/elasticsearch/index/engine/NoOpEngineTests.java

@@ -0,0 +1,221 @@
+/*
+ * 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.index.engine;
+
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.MergePolicy;
+import org.apache.lucene.index.NoMergePolicy;
+import org.apache.lucene.store.LockObtainFailedException;
+import org.elasticsearch.cluster.routing.IndexShardRoutingTable;
+import org.elasticsearch.cluster.routing.ShardRouting;
+import org.elasticsearch.cluster.routing.ShardRoutingState;
+import org.elasticsearch.cluster.routing.TestShardRouting;
+import org.elasticsearch.common.bytes.BytesArray;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.core.internal.io.IOUtils;
+import org.elasticsearch.index.IndexSettings;
+import org.elasticsearch.index.mapper.ParsedDocument;
+import org.elasticsearch.index.seqno.ReplicationTracker;
+import org.elasticsearch.index.seqno.SequenceNumbers;
+import org.elasticsearch.index.shard.DocsStats;
+import org.elasticsearch.index.store.Store;
+import org.elasticsearch.index.translog.Translog;
+import org.elasticsearch.index.translog.TranslogCorruptedException;
+import org.elasticsearch.index.translog.TranslogDeletionPolicy;
+import org.elasticsearch.test.IndexSettingsModule;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.Path;
+import java.util.Collections;
+import java.util.concurrent.atomic.AtomicLong;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.instanceOf;
+import static org.hamcrest.Matchers.is;
+
+public class NoOpEngineTests extends EngineTestCase {
+    private static final IndexSettings INDEX_SETTINGS = IndexSettingsModule.newIndexSettings("index", Settings.EMPTY);
+
+    public void testNoopEngine() throws IOException {
+        engine.close();
+        final NoOpEngine engine = new NoOpEngine(noOpConfig(INDEX_SETTINGS, store, primaryTranslogDir));
+        expectThrows(UnsupportedOperationException.class, () -> engine.syncFlush(null, null));
+        expectThrows(UnsupportedOperationException.class, () -> engine.ensureTranslogSynced(null));
+        assertThat(engine.refreshNeeded(), equalTo(false));
+        assertThat(engine.shouldPeriodicallyFlush(), equalTo(false));
+        engine.close();
+    }
+
+    public void testTwoNoopEngines() throws IOException {
+        engine.close();
+        // Ensure that we can't open two noop engines for the same store
+        final EngineConfig engineConfig = noOpConfig(INDEX_SETTINGS, store, primaryTranslogDir);
+        try (NoOpEngine ignored = new NoOpEngine(engineConfig)) {
+            UncheckedIOException e = expectThrows(UncheckedIOException.class, () -> new NoOpEngine(engineConfig));
+            assertThat(e.getCause(), instanceOf(LockObtainFailedException.class));
+        }
+    }
+
+    public void testNoopAfterRegularEngine() throws IOException {
+        int docs = randomIntBetween(1, 10);
+        ReplicationTracker tracker = (ReplicationTracker) engine.config().getGlobalCheckpointSupplier();
+        ShardRouting routing = TestShardRouting.newShardRouting("test", shardId.id(), "node",
+            null, true, ShardRoutingState.STARTED, allocationId);
+        IndexShardRoutingTable table = new IndexShardRoutingTable.Builder(shardId).addShard(routing).build();
+        tracker.updateFromMaster(1L, Collections.singleton(allocationId.getId()), table, Collections.emptySet());
+        tracker.activatePrimaryMode(SequenceNumbers.NO_OPS_PERFORMED);
+        for (int i = 0; i < docs; i++) {
+            ParsedDocument doc = testParsedDocument("" + i, null, testDocumentWithTextField(), B_1, null);
+            engine.index(indexForDoc(doc));
+            tracker.updateLocalCheckpoint(allocationId.getId(), i);
+        }
+
+        flushAndTrimTranslog(engine);
+
+        long localCheckpoint = engine.getLocalCheckpoint();
+        long maxSeqNo = engine.getSeqNoStats(100L).getMaxSeqNo();
+        engine.close();
+
+        final NoOpEngine noOpEngine = new NoOpEngine(noOpConfig(INDEX_SETTINGS, store, primaryTranslogDir, tracker));
+        assertThat(noOpEngine.getLocalCheckpoint(), equalTo(localCheckpoint));
+        assertThat(noOpEngine.getSeqNoStats(100L).getMaxSeqNo(), equalTo(maxSeqNo));
+        try (Engine.IndexCommitRef ref = noOpEngine.acquireLastIndexCommit(false)) {
+            try (IndexReader reader = DirectoryReader.open(ref.getIndexCommit())) {
+                assertThat(reader.numDocs(), equalTo(docs));
+            }
+        }
+        noOpEngine.close();
+    }
+
+    public void testNoopEngineWithInvalidTranslogUUID() throws IOException {
+        IOUtils.close(engine, store);
+        final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
+        try (Store store = createStore()) {
+            EngineConfig config = config(defaultSettings, store, createTempDir(), newMergePolicy(), null, null, globalCheckpoint::get);
+            int numDocs = scaledRandomIntBetween(10, 100);
+            try (InternalEngine engine = createEngine(config)) {
+                for (int i = 0; i < numDocs; i++) {
+                    ParsedDocument doc = testParsedDocument(Integer.toString(i), null, testDocument(), new BytesArray("{}"), null);
+                    engine.index(new Engine.Index(newUid(doc), doc, i, primaryTerm.get(), 1, null, Engine.Operation.Origin.REPLICA,
+                        System.nanoTime(), -1, false));
+                    if (rarely()) {
+                        engine.flush();
+                    }
+                    globalCheckpoint.set(engine.getLocalCheckpoint());
+                }
+                flushAndTrimTranslog(engine);
+            }
+
+            final Path newTranslogDir = createTempDir();
+            // A new translog will have a different UUID than the existing store/noOp engine does
+            Translog newTranslog = createTranslog(newTranslogDir, () -> 1L);
+            newTranslog.close();
+
+            EngineCreationFailureException e = expectThrows(EngineCreationFailureException.class,
+                () -> new NoOpEngine(noOpConfig(INDEX_SETTINGS, store, newTranslogDir)));
+            assertThat(e.getCause(), instanceOf(TranslogCorruptedException.class));
+        }
+    }
+
+    public void testNoopEngineWithNonZeroTranslogOperations() throws IOException {
+        IOUtils.close(engine, store);
+        final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
+        try (Store store = createStore()) {
+            final MergePolicy mergePolicy = NoMergePolicy.INSTANCE;
+            EngineConfig config = config(defaultSettings, store, createTempDir(), mergePolicy, null, null, globalCheckpoint::get);
+            int numDocs = scaledRandomIntBetween(10, 100);
+            try (InternalEngine engine = createEngine(config)) {
+                for (int i = 0; i < numDocs; i++) {
+                    ParsedDocument doc = testParsedDocument(Integer.toString(i), null, testDocument(), new BytesArray("{}"), null);
+                    engine.index(new Engine.Index(newUid(doc), doc, i, primaryTerm.get(), 1, null, Engine.Operation.Origin.REPLICA,
+                        System.nanoTime(), -1, false));
+                    if (rarely()) {
+                        engine.flush();
+                    }
+                    globalCheckpoint.set(engine.getLocalCheckpoint());
+                }
+                engine.syncTranslog();
+                engine.flushAndClose();
+                engine.close();
+
+                IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> new NoOpEngine(engine.engineConfig));
+                assertThat(e.getMessage(), is("Expected 0 translog operations but there were " + numDocs));
+            }
+        }
+    }
+
+    public void testNoOpEngineDocStats() throws Exception {
+        IOUtils.close(engine, store);
+        final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
+        try (Store store = createStore()) {
+            EngineConfig config = config(defaultSettings, store, createTempDir(), newMergePolicy(), null, null, globalCheckpoint::get);
+            final int numDocs = scaledRandomIntBetween(10, 3000);
+            int deletions = 0;
+            try (InternalEngine engine = createEngine(config)) {
+                for (int i = 0; i < numDocs; i++) {
+                    engine.index(indexForDoc(createParsedDoc(Integer.toString(i), null)));
+                    if (rarely()) {
+                        engine.flush();
+                    }
+                    globalCheckpoint.set(engine.getLocalCheckpoint());
+                }
+
+                for (int i = 0; i < numDocs; i++) {
+                    if (randomBoolean()) {
+                        String delId = Integer.toString(i);
+                        Engine.DeleteResult result = engine.delete(new Engine.Delete("test", delId, newUid(delId), primaryTerm.get()));
+                        assertTrue(result.isFound());
+                        globalCheckpoint.set(engine.getLocalCheckpoint());
+                        deletions += 1;
+                    }
+                }
+                engine.waitForOpsToComplete(numDocs + deletions - 1);
+                flushAndTrimTranslog(engine);
+                engine.close();
+            }
+
+            final DocsStats expectedDocStats;
+            try (InternalEngine engine = createEngine(config)) {
+                expectedDocStats = engine.docStats();
+            }
+
+            try (NoOpEngine noOpEngine = new NoOpEngine(config)) {
+                assertEquals(expectedDocStats.getCount(), noOpEngine.docStats().getCount());
+                assertEquals(expectedDocStats.getDeleted(), noOpEngine.docStats().getDeleted());
+                assertEquals(expectedDocStats.getTotalSizeInBytes(), noOpEngine.docStats().getTotalSizeInBytes());
+                assertEquals(expectedDocStats.getAverageSizeInBytes(), noOpEngine.docStats().getAverageSizeInBytes());
+            } catch (AssertionError e) {
+                logger.error(config.getMergePolicy());
+                throw e;
+            }
+        }
+    }
+
+    private void flushAndTrimTranslog(final InternalEngine engine) {
+        engine.flush(true, true);
+        final TranslogDeletionPolicy deletionPolicy = engine.getTranslog().getDeletionPolicy();
+        deletionPolicy.setRetentionSizeInBytes(-1);
+        deletionPolicy.setRetentionAgeInMillis(-1);
+        deletionPolicy.setMinTranslogGenerationForRecovery(engine.getTranslog().getGeneration().translogFileGeneration);
+        engine.flush(true, true);
+    }
+}