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Elasticsearch - Open Source, Distributed, RESTful Search Engine
/*
* 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.SegmentInfos;
import org.apache.lucene.search.SearcherFactory;
import org.apache.lucene.search.SearcherManager;
import org.apache.lucene.store.AlreadyClosedException;
import org.apache.lucene.util.IOUtils;
import org.elasticsearch.common.lucene.Lucene;
import org.elasticsearch.common.lucene.index.ElasticsearchDirectoryReader;
import org.elasticsearch.common.unit.TimeValue;
import org.elasticsearch.common.util.concurrent.ReleasableLock;
import org.elasticsearch.index.deletionpolicy.SnapshotIndexCommit;
import org.elasticsearch.index.translog.Translog;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
/**
* ShadowEngine is a specialized engine that only allows read-only operations
* on the underlying Lucene index. An {@code IndexReader} is opened instead of
* an {@code IndexWriter}. All methods that would usually perform write
* operations are no-ops, this means:
*
* - No operations are written to or read from the translog
* - Create, Index, and Delete do nothing
* - Flush does not fsync any files, or make any on-disk changes
*
* In order for new segments to become visible, the ShadowEngine may perform
* stage1 of the traditional recovery process (copying segment files) from a
* regular primary (which uses {@link org.elasticsearch.index.engine.InternalEngine})
*
* Notice that since this Engine does not deal with the translog, any
* {@link #get(Get get)} request goes directly to the searcher, meaning it is
* non-realtime.
*/
public class ShadowEngine extends Engine {
/** how long to wait for an index to exist */
public final static String NONEXISTENT_INDEX_RETRY_WAIT = "index.shadow.wait_for_initial_commit";
public final static TimeValue DEFAULT_NONEXISTENT_INDEX_RETRY_WAIT = TimeValue.timeValueSeconds(5);
private volatile SearcherManager searcherManager;
private volatile SegmentInfos lastCommittedSegmentInfos;
public ShadowEngine(EngineConfig engineConfig) {
super(engineConfig);
SearcherFactory searcherFactory = new EngineSearcherFactory(engineConfig);
final long nonexistentRetryTime = engineConfig.getIndexSettings()
.getAsTime(NONEXISTENT_INDEX_RETRY_WAIT, DEFAULT_NONEXISTENT_INDEX_RETRY_WAIT)
.getMillis();
try {
DirectoryReader reader = null;
store.incRef();
boolean success = false;
try {
if (Lucene.waitForIndex(store.directory(), nonexistentRetryTime)) {
reader = ElasticsearchDirectoryReader.wrap(DirectoryReader.open(store.directory()), shardId);
this.searcherManager = new SearcherManager(reader, searcherFactory);
this.lastCommittedSegmentInfos = readLastCommittedSegmentInfos(searcherManager, store);
success = true;
} else {
throw new IllegalStateException("failed to open a shadow engine after" +
nonexistentRetryTime + "ms, " +
"directory is not an index");
}
} catch (Throwable e) {
logger.warn("failed to create new reader", e);
throw e;
} finally {
if (success == false) {
IOUtils.closeWhileHandlingException(reader);
store.decRef();
}
}
} catch (IOException ex) {
throw new EngineCreationFailureException(shardId, "failed to open index reader", ex);
}
logger.trace("created new ShadowEngine");
}
@Override
public void create(Create create) throws EngineException {
throw new UnsupportedOperationException(shardId + " create operation not allowed on shadow engine");
}
@Override
public boolean index(Index index) throws EngineException {
throw new UnsupportedOperationException(shardId + " index operation not allowed on shadow engine");
}
@Override
public void delete(Delete delete) throws EngineException {
throw new UnsupportedOperationException(shardId + " delete operation not allowed on shadow engine");
}
/** @deprecated This was removed, but we keep this API so translog can replay any DBQs on upgrade. */
@Deprecated
@Override
public void delete(DeleteByQuery delete) throws EngineException {
throw new UnsupportedOperationException(shardId + " delete-by-query operation not allowed on shadow engine");
}
@Override
public SyncedFlushResult syncFlush(String syncId, CommitId expectedCommitId) {
throw new UnsupportedOperationException(shardId + " sync commit operation not allowed on shadow engine");
}
@Override
public CommitId flush() throws EngineException {
return flush(false, false);
}
@Override
public CommitId flush(boolean force, boolean waitIfOngoing) throws EngineException {
logger.trace("skipping FLUSH on shadow engine");
// reread the last committed segment infos
refresh("flush");
/*
* we have to inc-ref the store here since if the engine is closed by a tragic event
* we don't acquire the write lock and wait until we have exclusive access. This might also
* dec the store reference which can essentially close the store and unless we can inc the reference
* we can't use it.
*/
store.incRef();
try (ReleasableLock lock = readLock.acquire()) {
// reread the last committed segment infos
lastCommittedSegmentInfos = readLastCommittedSegmentInfos(searcherManager, store);
} catch (Throwable e) {
if (isClosed.get() == false) {
logger.warn("failed to read latest segment infos on flush", e);
if (Lucene.isCorruptionException(e)) {
throw new FlushFailedEngineException(shardId, e);
}
}
} finally {
store.decRef();
}
return new CommitId(lastCommittedSegmentInfos.getId());
}
@Override
public void forceMerge(boolean flush, int maxNumSegments, boolean onlyExpungeDeletes, boolean upgrade, boolean upgradeOnlyAncientSegments) throws EngineException {
// no-op
logger.trace("skipping FORCE-MERGE on shadow engine");
}
@Override
public GetResult get(Get get) throws EngineException {
// There is no translog, so we can get it directly from the searcher
return getFromSearcher(get);
}
@Override
public Translog getTranslog() {
throw new UnsupportedOperationException("shadow engines don't have translogs");
}
@Override
public List segments(boolean verbose) {
try (ReleasableLock lock = readLock.acquire()) {
Segment[] segmentsArr = getSegmentInfo(lastCommittedSegmentInfos, verbose);
for (int i = 0; i < segmentsArr.length; i++) {
// hard code all segments as committed, because they are in
// order for the shadow replica to see them
segmentsArr[i].committed = true;
}
return Arrays.asList(segmentsArr);
}
}
@Override
public void refresh(String source) throws EngineException {
// we obtain a read lock here, since we don't want a flush to happen while we are refreshing
// since it flushes the index as well (though, in terms of concurrency, we are allowed to do it)
try (ReleasableLock lock = readLock.acquire()) {
ensureOpen();
searcherManager.maybeRefreshBlocking();
} catch (AlreadyClosedException e) {
ensureOpen();
} catch (EngineClosedException e) {
throw e;
} catch (Throwable t) {
failEngine("refresh failed", t);
throw new RefreshFailedEngineException(shardId, t);
}
}
@Override
public SnapshotIndexCommit snapshotIndex(boolean flushFirst) throws EngineException {
throw new UnsupportedOperationException("Can not take snapshot from a shadow engine");
}
@Override
protected SearcherManager getSearcherManager() {
return searcherManager;
}
@Override
protected void closeNoLock(String reason) {
if (isClosed.compareAndSet(false, true)) {
try {
logger.debug("shadow replica close searcher manager refCount: {}", store.refCount());
IOUtils.close(searcherManager);
} catch (Throwable t) {
logger.warn("shadow replica failed to close searcher manager", t);
} finally {
store.decRef();
}
}
}
@Override
public boolean hasUncommittedChanges() {
return false;
}
@Override
protected SegmentInfos getLastCommittedSegmentInfos() {
return lastCommittedSegmentInfos;
}
@Override
public long indexWriterRAMBytesUsed() {
// No IndexWriter
throw new UnsupportedOperationException("ShadowEngine has no IndexWriter");
}
}