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[RCI] Add NoOpEngine for closed indices (#33903)
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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
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tlrx committed Oct 26, 2018
1 parent 33345d9 commit 8e93bc4
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Showing 7 changed files with 423 additions and 4 deletions.
149 changes: 149 additions & 0 deletions server/src/main/java/org/elasticsearch/index/engine/NoOpEngine.java
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/*
* 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");
}
}
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*
* @see #ReadOnlyEngine(EngineConfig, SeqNoStats, TranslogStats, boolean, Function)
*/
public final class ReadOnlyEngine extends Engine {
public class ReadOnlyEngine extends Engine {

private final SegmentInfos lastCommittedSegmentInfos;
private final SeqNoStats seqNoStats;
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Expand Up @@ -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;
Expand Down Expand Up @@ -517,6 +518,12 @@ 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()
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