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FrozenEngine.java
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FrozenEngine.java
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/*
* Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
* or more contributor license agreements. Licensed under the Elastic License;
* you may not use this file except in compliance with the Elastic License.
*/
package org.elasticsearch.index.engine;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexCommit;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.LeafReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.SegmentReader;
import org.apache.lucene.index.SoftDeletesDirectoryReaderWrapper;
import org.apache.lucene.search.ReferenceManager;
import org.apache.lucene.store.Directory;
import org.elasticsearch.common.SuppressForbidden;
import org.elasticsearch.common.lucene.Lucene;
import org.elasticsearch.common.lucene.index.ElasticsearchDirectoryReader;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.core.internal.io.IOUtils;
import org.elasticsearch.index.shard.DocsStats;
import org.elasticsearch.index.store.Store;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.util.concurrent.CountDownLatch;
import java.util.function.Function;
/**
* This is a stand-alone read-only engine that maintains an index reader that is opened lazily on calls to
* {@link SearcherSupplier#acquireSearcher(String)}. The index reader opened is maintained until there are no reference to it anymore
* and then releases itself from the engine.
* This is necessary to for instance release all SegmentReaders after a search phase finishes and reopen them before the next search
* phase starts.
* This together with a throttled threadpool (search_throttled) guarantees that at most N frozen shards have a low level index reader
* open at the same time.
* The internal reopen of readers is treated like a refresh and refresh listeners are called up-on reopen. This allows to consume refresh
* stats in order to obtain the number of reopens.
*/
public final class FrozenEngine extends ReadOnlyEngine {
public static final Setting<Boolean> INDEX_FROZEN = Setting.boolSetting("index.frozen", false, Setting.Property.IndexScope,
Setting.Property.PrivateIndex);
private final SegmentsStats segmentsStats;
private final DocsStats docsStats;
private volatile ElasticsearchDirectoryReader lastOpenedReader;
private final ElasticsearchDirectoryReader canMatchReader;
public FrozenEngine(EngineConfig config, boolean requireCompleteHistory) {
super(config, null, null, true, Function.identity(), requireCompleteHistory);
boolean success = false;
Directory directory = store.directory();
try (DirectoryReader reader = openDirectory(directory)) {
// we record the segment stats and doc stats here - that's what the reader needs when it's open and it give the user
// an idea of what it can save when it's closed
this.segmentsStats = new SegmentsStats();
for (LeafReaderContext ctx : reader.getContext().leaves()) {
SegmentReader segmentReader = Lucene.segmentReader(ctx.reader());
fillSegmentStats(segmentReader, true, segmentsStats);
}
this.docsStats = docsStats(reader);
final DirectoryReader wrappedReader = new SoftDeletesDirectoryReaderWrapper(reader, Lucene.SOFT_DELETES_FIELD);
canMatchReader = ElasticsearchDirectoryReader.wrap(
new RewriteCachingDirectoryReader(directory, wrappedReader.leaves()), config.getShardId());
success = true;
} catch (IOException e) {
throw new UncheckedIOException(e);
} finally {
if (success == false) {
closeNoLock("failed on construction", new CountDownLatch(1));
}
}
}
@Override
protected DirectoryReader open(IndexCommit indexCommit) throws IOException {
// we fake an empty DirectoryReader for the ReadOnlyEngine. this reader is only used
// to initialize the reference manager and to make the refresh call happy which is essentially
// a no-op now
return new DirectoryReader(indexCommit.getDirectory(), new LeafReader[0]) {
@Override
protected DirectoryReader doOpenIfChanged() {
return null;
}
@Override
protected DirectoryReader doOpenIfChanged(IndexCommit commit) {
return null;
}
@Override
protected DirectoryReader doOpenIfChanged(IndexWriter writer, boolean applyAllDeletes) {
return null;
}
@Override
public long getVersion() {
return 0;
}
@Override
public boolean isCurrent() {
return true; // always current
}
@Override
public IndexCommit getIndexCommit() {
return indexCommit; // TODO maybe we can return an empty commit?
}
@Override
protected void doClose() {
}
@Override
public CacheHelper getReaderCacheHelper() {
return null;
}
};
}
@SuppressForbidden(reason = "we manage references explicitly here")
private synchronized void onReaderClosed(IndexReader.CacheKey key) {
// it might look awkward that we have to check here if the keys match but if we concurrently
// access the lastOpenedReader there might be 2 threads competing for the cached reference in
// a way that thread 1 counts down the lastOpenedReader reference and before thread 1 can execute
// the close listener we already open and assign a new reader to lastOpenedReader. In this case
// the cache key doesn't match and we just ignore it since we use this method only to null out the
// lastOpenedReader member to ensure resources can be GCed
if (lastOpenedReader != null && key == lastOpenedReader.getReaderCacheHelper().getKey()) {
assert lastOpenedReader.getRefCount() == 0;
lastOpenedReader = null;
}
}
@SuppressForbidden(reason = "we manage references explicitly here")
private synchronized void closeReader(IndexReader reader) throws IOException {
reader.decRef();
}
private synchronized ElasticsearchDirectoryReader getOrOpenReader() throws IOException {
ElasticsearchDirectoryReader reader = null;
boolean success = false;
try {
reader = getReader();
if (reader == null) {
for (ReferenceManager.RefreshListener listeners : config ().getInternalRefreshListener()) {
listeners.beforeRefresh();
}
final DirectoryReader dirReader = openDirectory(engineConfig.getStore().directory());
reader = lastOpenedReader = wrapReader(dirReader, Function.identity());
processReader(reader);
reader.getReaderCacheHelper().addClosedListener(this::onReaderClosed);
for (ReferenceManager.RefreshListener listeners : config().getInternalRefreshListener()) {
listeners.afterRefresh(true);
}
}
success = true;
return reader;
} finally {
if (success == false) {
IOUtils.close(reader);
}
}
}
@SuppressForbidden(reason = "we manage references explicitly here")
private synchronized ElasticsearchDirectoryReader getReader() {
if (lastOpenedReader != null && lastOpenedReader.tryIncRef()) {
return lastOpenedReader;
}
return null;
}
@Override
public SearcherSupplier acquireSearcherSupplier(Function<Searcher, Searcher> wrapper, SearcherScope scope) throws EngineException {
final Store store = this.store;
store.incRef();
return new SearcherSupplier(wrapper) {
@Override
@SuppressForbidden(reason = "we manage references explicitly here")
public Searcher acquireSearcherInternal(String source) {
try {
return openSearcher(source, scope);
} catch (IOException exc) {
throw new UncheckedIOException(exc);
}
}
@Override
protected void doClose() {
store.decRef();
}
@Override
public String getCommitId() {
return commitId;
}
};
}
@SuppressWarnings("fallthrough")
@SuppressForbidden(reason = "we manage references explicitly here")
private Engine.Searcher openSearcher(String source, SearcherScope scope) throws IOException {
boolean maybeOpenReader;
switch (source) {
case "load_seq_no":
case "load_version":
assert false : "this is a read-only engine";
case "doc_stats":
assert false : "doc_stats are overwritten";
case "refresh_needed":
assert false : "refresh_needed is always false";
case "segments":
case "segments_stats":
case "completion_stats":
case CAN_MATCH_SEARCH_SOURCE: // special case for can_match phase - we use the cached point values reader
maybeOpenReader = false;
break;
default:
maybeOpenReader = true;
}
ElasticsearchDirectoryReader reader = maybeOpenReader ? getOrOpenReader() : getReader();
if (reader == null) {
if (CAN_MATCH_SEARCH_SOURCE.equals(source)) {
canMatchReader.incRef();
return new Searcher(source, canMatchReader, engineConfig.getSimilarity(), engineConfig.getQueryCache(),
engineConfig.getQueryCachingPolicy(), canMatchReader::decRef);
} else {
ReferenceManager<ElasticsearchDirectoryReader> manager = getReferenceManager(scope);
ElasticsearchDirectoryReader acquire = manager.acquire();
return new Searcher(source, acquire, engineConfig.getSimilarity(), engineConfig.getQueryCache(),
engineConfig.getQueryCachingPolicy(), () -> manager.release(acquire));
}
} else {
return new Searcher(source, reader, engineConfig.getSimilarity(), engineConfig.getQueryCache(),
engineConfig.getQueryCachingPolicy(), () -> closeReader(reader));
}
}
@Override
public SegmentsStats segmentsStats(boolean includeSegmentFileSizes, boolean includeUnloadedSegments) {
if (includeUnloadedSegments) {
final SegmentsStats stats = new SegmentsStats();
stats.add(this.segmentsStats);
if (includeSegmentFileSizes == false) {
stats.clearFileSizes();
}
return stats;
} else {
return super.segmentsStats(includeSegmentFileSizes, includeUnloadedSegments);
}
}
@Override
public DocsStats docStats() {
return docsStats;
}
synchronized boolean isReaderOpen() {
return lastOpenedReader != null;
} // this is mainly for tests
}