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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.indices;
import com.carrotsearch.hppc.ObjectHashSet;
import com.carrotsearch.hppc.ObjectSet;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.RamUsageEstimator;
import org.elasticsearch.common.bytes.BytesReference;
import org.elasticsearch.common.cache.Cache;
import org.elasticsearch.common.cache.CacheBuilder;
import org.elasticsearch.common.cache.CacheLoader;
import org.elasticsearch.common.cache.RemovalListener;
import org.elasticsearch.common.cache.RemovalNotification;
import org.elasticsearch.common.component.AbstractComponent;
import org.elasticsearch.common.lucene.index.ElasticsearchDirectoryReader;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Setting.Property;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.unit.ByteSizeValue;
import org.elasticsearch.common.unit.TimeValue;
import org.elasticsearch.common.util.concurrent.ConcurrentCollections;
import java.io.Closeable;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.function.Supplier;
/**
* The indices request cache allows to cache a shard level request stage responses, helping with improving
* similar requests that are potentially expensive (because of aggs for example). The cache is fully coherent
* with the semantics of NRT (the index reader version is part of the cache key), and relies on size based
* eviction to evict old reader associated cache entries as well as scheduler reaper to clean readers that
* are no longer used or closed shards.
*
* Currently, the cache is only enabled for count requests, and can only be opted in on an index
* level setting that can be dynamically changed and defaults to false.
*
* There are still several TODOs left in this class, some easily addressable, some more complex, but the support
* is functional.
*/
public final class IndicesRequestCache extends AbstractComponent implements RemovalListener, Closeable {
/**
* A setting to enable or disable request caching on an index level. Its dynamic by default
* since we are checking on the cluster state IndexMetaData always.
*/
public static final Setting INDEX_CACHE_REQUEST_ENABLED_SETTING =
Setting.boolSetting("index.requests.cache.enable", true, Property.Dynamic, Property.IndexScope);
public static final Setting INDICES_CACHE_QUERY_SIZE =
Setting.memorySizeSetting("indices.requests.cache.size", "1%", Property.NodeScope);
public static final Setting INDICES_CACHE_QUERY_EXPIRE =
Setting.positiveTimeSetting("indices.requests.cache.expire", new TimeValue(0), Property.NodeScope);
private final ConcurrentMap registeredClosedListeners = ConcurrentCollections.newConcurrentMap();
private final Set keysToClean = ConcurrentCollections.newConcurrentSet();
private final ByteSizeValue size;
private final TimeValue expire;
private final Cache cache;
IndicesRequestCache(Settings settings) {
super(settings);
this.size = INDICES_CACHE_QUERY_SIZE.get(settings);
this.expire = INDICES_CACHE_QUERY_EXPIRE.exists(settings) ? INDICES_CACHE_QUERY_EXPIRE.get(settings) : null;
long sizeInBytes = size.getBytes();
CacheBuilder cacheBuilder = CacheBuilder.builder()
.setMaximumWeight(sizeInBytes).weigher((k, v) -> k.ramBytesUsed() + v.ramBytesUsed()).removalListener(this);
if (expire != null) {
cacheBuilder.setExpireAfterAccess(expire);
}
cache = cacheBuilder.build();
}
@Override
public void close() {
cache.invalidateAll();
}
void clear(CacheEntity entity) {
keysToClean.add(new CleanupKey(entity, -1));
cleanCache();
}
@Override
public void onRemoval(RemovalNotification notification) {
notification.getKey().entity.onRemoval(notification);
}
BytesReference getOrCompute(CacheEntity cacheEntity, Supplier loader,
DirectoryReader reader, BytesReference cacheKey) throws Exception {
final Key key = new Key(cacheEntity, reader.getVersion(), cacheKey);
Loader cacheLoader = new Loader(cacheEntity, loader);
BytesReference value = cache.computeIfAbsent(key, cacheLoader);
if (cacheLoader.isLoaded()) {
key.entity.onMiss();
// see if its the first time we see this reader, and make sure to register a cleanup key
CleanupKey cleanupKey = new CleanupKey(cacheEntity, reader.getVersion());
if (!registeredClosedListeners.containsKey(cleanupKey)) {
Boolean previous = registeredClosedListeners.putIfAbsent(cleanupKey, Boolean.TRUE);
if (previous == null) {
ElasticsearchDirectoryReader.addReaderCloseListener(reader, cleanupKey);
}
}
} else {
key.entity.onHit();
}
return value;
}
/**
* Invalidates the given the cache entry for the given key and it's context
* @param cacheEntity the cache entity to invalidate for
* @param reader the reader to invalidate the cache entry for
* @param cacheKey the cache key to invalidate
*/
void invalidate(CacheEntity cacheEntity, DirectoryReader reader, BytesReference cacheKey) {
cache.invalidate(new Key(cacheEntity, reader.getVersion(), cacheKey));
}
private static class Loader implements CacheLoader {
private final CacheEntity entity;
private final Supplier loader;
private boolean loaded;
Loader(CacheEntity entity, Supplier loader) {
this.entity = entity;
this.loader = loader;
}
public boolean isLoaded() {
return this.loaded;
}
@Override
public BytesReference load(Key key) throws Exception {
BytesReference value = loader.get();
entity.onCached(key, value);
loaded = true;
return value;
}
}
/**
* Basic interface to make this cache testable.
*/
interface CacheEntity extends Accountable {
/**
* Called after the value was loaded.
*/
void onCached(Key key, BytesReference value);
/**
* Returns true iff the resource behind this entity is still open ie.
* entities assiciated with it can remain in the cache. ie. IndexShard is still open.
*/
boolean isOpen();
/**
* Returns the cache identity. this is, similar to {@link #isOpen()} the resource identity behind this cache entity.
* For instance IndexShard is the identity while a CacheEntity is per DirectoryReader. Yet, we group by IndexShard instance.
*/
Object getCacheIdentity();
/**
* Called each time this entity has a cache hit.
*/
void onHit();
/**
* Called each time this entity has a cache miss.
*/
void onMiss();
/**
* Called when this entity instance is removed
*/
void onRemoval(RemovalNotification notification);
}
static class Key implements Accountable {
private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(Key.class);
public final CacheEntity entity; // use as identity equality
public final long readerVersion; // use the reader version to now keep a reference to a "short" lived reader until its reaped
public final BytesReference value;
Key(CacheEntity entity, long readerVersion, BytesReference value) {
this.entity = entity;
this.readerVersion = readerVersion;
this.value = value;
}
@Override
public long ramBytesUsed() {
return BASE_RAM_BYTES_USED + entity.ramBytesUsed() + value.length();
}
@Override
public Collection getChildResources() {
// TODO: more detailed ram usage?
return Collections.emptyList();
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
Key key = (Key) o;
if (readerVersion != key.readerVersion) return false;
if (!entity.getCacheIdentity().equals(key.entity.getCacheIdentity())) return false;
if (!value.equals(key.value)) return false;
return true;
}
@Override
public int hashCode() {
int result = entity.getCacheIdentity().hashCode();
result = 31 * result + Long.hashCode(readerVersion);
result = 31 * result + value.hashCode();
return result;
}
}
private class CleanupKey implements IndexReader.ReaderClosedListener {
final CacheEntity entity;
final long readerVersion; // use the reader version to now keep a reference to a "short" lived reader until its reaped
private CleanupKey(CacheEntity entity, long readerVersion) {
this.entity = entity;
this.readerVersion = readerVersion;
}
@Override
public void onClose(IndexReader reader) {
Boolean remove = registeredClosedListeners.remove(this);
if (remove != null) {
keysToClean.add(this);
}
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
CleanupKey that = (CleanupKey) o;
if (readerVersion != that.readerVersion) return false;
if (!entity.getCacheIdentity().equals(that.entity.getCacheIdentity())) return false;
return true;
}
@Override
public int hashCode() {
int result = entity.getCacheIdentity().hashCode();
result = 31 * result + Long.hashCode(readerVersion);
return result;
}
}
synchronized void cleanCache() {
final ObjectSet currentKeysToClean = new ObjectHashSet<>();
final ObjectSet