Move the IndexDeletionPolicy to be engine internal (#24930)

The `IndexDeletionPolicy` is currently instantiated by `IndexShard` and is then passed through to the engine as a parameter. That's a shame as it is really just an implementation detail and the engine already has a method to acquire a commit.

This is preparing for a follow up PR that will we connect the index deletion policy with a new translog deletion policy.

Relates to #10708

core/src/main/java/org/elasticsearch/index/engine/Engine.java

@@ -44,6 +44,7 @@
 import org.apache.lucene.util.Accountables;
 import org.apache.lucene.util.SetOnce;
 import org.elasticsearch.ExceptionsHelper;
+import org.elasticsearch.common.CheckedRunnable;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.collect.ImmutableOpenMap;
@@ -63,7 +64,6 @@
 import org.elasticsearch.index.VersionType;
 import org.elasticsearch.index.mapper.ParseContext.Document;
 import org.elasticsearch.index.mapper.ParsedDocument;
-import org.elasticsearch.index.mapper.Uid;
 import org.elasticsearch.index.merge.MergeStats;
 import org.elasticsearch.index.seqno.SequenceNumbersService;
 import org.elasticsearch.index.shard.ShardId;
@@ -100,7 +100,6 @@ public abstract class Engine implements Closeable {
     protected final Store store;
     protected final AtomicBoolean isClosed = new AtomicBoolean(false);
     protected final EventListener eventListener;
-    protected final SnapshotDeletionPolicy deletionPolicy;
     protected final ReentrantLock failEngineLock = new ReentrantLock();
     protected final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
     protected final ReleasableLock readLock = new ReleasableLock(rwl.readLock());
@@ -121,15 +120,13 @@ public abstract class Engine implements Closeable {
 
     protected Engine(EngineConfig engineConfig) {
         Objects.requireNonNull(engineConfig.getStore(), "Store must be provided to the engine");
-        Objects.requireNonNull(engineConfig.getDeletionPolicy(), "Snapshot deletion policy must be provided to the engine");
 
         this.engineConfig = engineConfig;
         this.shardId = engineConfig.getShardId();
         this.store = engineConfig.getStore();
         this.logger = Loggers.getLogger(Engine.class, // we use the engine class directly here to make sure all subclasses have the same logger name
                 engineConfig.getIndexSettings().getSettings(), engineConfig.getShardId());
         this.eventListener = engineConfig.getEventListener();
-        this.deletionPolicy = engineConfig.getDeletionPolicy();
     }
 
     /** Returns 0 in the case where accountable is null, otherwise returns {@code ramBytesUsed()} */
@@ -828,7 +825,7 @@ public void forceMerge(boolean flush) throws IOException {
      *
      * @param flushFirst indicates whether the engine should flush before returning the snapshot
      */
-    public abstract IndexCommit acquireIndexCommit(boolean flushFirst) throws EngineException;
+    public abstract IndexCommitRef acquireIndexCommit(boolean flushFirst) throws EngineException;
 
     /**
      * fail engine due to some error. the engine will also be closed.
@@ -1387,6 +1384,28 @@ public int hashCode() {
         }
     }
 
+    public static class IndexCommitRef implements Closeable {
+        private final AtomicBoolean closed = new AtomicBoolean();
+        private final CheckedRunnable<IOException> onClose;
+        private final IndexCommit indexCommit;
+
+        IndexCommitRef(SnapshotDeletionPolicy deletionPolicy) throws IOException {
+            indexCommit = deletionPolicy.snapshot();
+            onClose = () -> deletionPolicy.release(indexCommit);
+        }
+
+        @Override
+        public void close() throws IOException {
+            if (closed.compareAndSet(false, true)) {
+                onClose.run();
+            }
+        }
+
+        public IndexCommit getIndexCommit() {
+            return indexCommit;
+        }
+    }
+
     public void onSettingsChanged() {
     }
 

core/src/main/java/org/elasticsearch/index/engine/EngineConfig.java

@@ -21,7 +21,6 @@
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.index.MergePolicy;
-import org.apache.lucene.index.SnapshotDeletionPolicy;
 import org.apache.lucene.search.QueryCache;
 import org.apache.lucene.search.QueryCachingPolicy;
 import org.apache.lucene.search.ReferenceManager;
@@ -58,7 +57,6 @@ public final class EngineConfig {
     private final ThreadPool threadPool;
     private final Engine.Warmer warmer;
     private final Store store;
-    private final SnapshotDeletionPolicy deletionPolicy;
     private final MergePolicy mergePolicy;
     private final Analyzer analyzer;
     private final Similarity similarity;
@@ -109,7 +107,7 @@ public final class EngineConfig {
      * Creates a new {@link org.elasticsearch.index.engine.EngineConfig}
      */
     public EngineConfig(OpenMode openMode, ShardId shardId, ThreadPool threadPool,
-                        IndexSettings indexSettings, Engine.Warmer warmer, Store store, SnapshotDeletionPolicy deletionPolicy,
+                        IndexSettings indexSettings, Engine.Warmer warmer, Store store,
                         MergePolicy mergePolicy, Analyzer analyzer,
                         Similarity similarity, CodecService codecService, Engine.EventListener eventListener,
                         TranslogRecoveryPerformer translogRecoveryPerformer, QueryCache queryCache, QueryCachingPolicy queryCachingPolicy,
@@ -123,7 +121,6 @@ public EngineConfig(OpenMode openMode, ShardId shardId, ThreadPool threadPool,
         this.threadPool = threadPool;
         this.warmer = warmer == null ? (a) -> {} : warmer;
         this.store = store;
-        this.deletionPolicy = deletionPolicy;
         this.mergePolicy = mergePolicy;
         this.analyzer = analyzer;
         this.similarity = similarity;
@@ -214,14 +211,6 @@ public Store getStore() {
         return store;
     }
 
-    /**
-     * Returns a {@link SnapshotDeletionPolicy} used in the engines
-     * {@link org.apache.lucene.index.IndexWriter}.
-     */
-    public SnapshotDeletionPolicy getDeletionPolicy() {
-        return deletionPolicy;
-    }
-
     /**
      * Returns the {@link org.apache.lucene.index.MergePolicy} for the engines {@link org.apache.lucene.index.IndexWriter}
      */

core/src/main/java/org/elasticsearch/index/engine/InternalEngine.java

@@ -21,16 +21,17 @@
 
 import org.apache.logging.log4j.Logger;
 import org.apache.lucene.index.DirectoryReader;
-import org.apache.lucene.index.IndexCommit;
 import org.apache.lucene.index.IndexFormatTooOldException;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.index.KeepOnlyLastCommitDeletionPolicy;
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LiveIndexWriterConfig;
 import org.apache.lucene.index.MergePolicy;
 import org.apache.lucene.index.SegmentCommitInfo;
 import org.apache.lucene.index.SegmentInfos;
+import org.apache.lucene.index.SnapshotDeletionPolicy;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.SearcherFactory;
@@ -126,6 +127,8 @@ public class InternalEngine extends Engine {
 
     private final String uidField;
 
+    private final SnapshotDeletionPolicy deletionPolicy;
+
     // How many callers are currently requesting index throttling.  Currently there are only two situations where we do this: when merges
     // are falling behind and when writing indexing buffer to disk is too slow.  When this is 0, there is no throttling, else we throttling
     // incoming indexing ops to a single thread:
@@ -137,12 +140,14 @@ public class InternalEngine extends Engine {
     private final CounterMetric numVersionLookups = new CounterMetric();
     private final CounterMetric numIndexVersionsLookups = new CounterMetric();
 
+
     public InternalEngine(EngineConfig engineConfig) throws EngineException {
         super(engineConfig);
         openMode = engineConfig.getOpenMode();
         if (engineConfig.isAutoGeneratedIDsOptimizationEnabled() == false) {
             maxUnsafeAutoIdTimestamp.set(Long.MAX_VALUE);
         }
+        deletionPolicy = new SnapshotDeletionPolicy(new KeepOnlyLastCommitDeletionPolicy());
         this.uidField = engineConfig.getIndexSettings().isSingleType() ? IdFieldMapper.NAME : UidFieldMapper.NAME;
         this.versionMap = new LiveVersionMap();
         store.incRef();
@@ -1414,7 +1419,7 @@ public void forceMerge(final boolean flush, int maxNumSegments, boolean onlyExpu
     }
 
     @Override
-    public IndexCommit acquireIndexCommit(final boolean flushFirst) throws EngineException {
+    public IndexCommitRef acquireIndexCommit(final boolean flushFirst) throws EngineException {
         // we have to flush outside of the readlock otherwise we might have a problem upgrading
         // the to a write lock when we fail the engine in this operation
         if (flushFirst) {
@@ -1425,7 +1430,7 @@ public IndexCommit acquireIndexCommit(final boolean flushFirst) throws EngineExc
         try (ReleasableLock lock = readLock.acquire()) {
             ensureOpen();
             logger.trace("pulling snapshot");
-            return deletionPolicy.snapshot();
+            return new IndexCommitRef(deletionPolicy);
         } catch (IOException e) {
             throw new SnapshotFailedEngineException(shardId, e);
         }

core/src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -23,9 +23,7 @@
 import org.apache.lucene.index.CheckIndex;
 import org.apache.lucene.index.IndexCommit;
 import org.apache.lucene.index.IndexOptions;
-import org.apache.lucene.index.KeepOnlyLastCommitDeletionPolicy;
 import org.apache.lucene.index.SegmentInfos;
-import org.apache.lucene.index.SnapshotDeletionPolicy;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.QueryCachingPolicy;
 import org.apache.lucene.search.Sort;
@@ -161,7 +159,6 @@ public class IndexShard extends AbstractIndexShardComponent implements IndicesCl
     private final String checkIndexOnStartup;
     private final CodecService codecService;
     private final Engine.Warmer warmer;
-    private final SnapshotDeletionPolicy deletionPolicy;
     private final SimilarityService similarityService;
     private final TranslogConfig translogConfig;
     private final IndexEventListener indexEventListener;
@@ -230,7 +227,6 @@ public IndexShard(ShardRouting shardRouting, IndexSettings indexSettings, ShardP
         final Settings settings = indexSettings.getSettings();
         this.codecService = new CodecService(mapperService, logger);
         this.warmer = warmer;
-        this.deletionPolicy = new SnapshotDeletionPolicy(new KeepOnlyLastCommitDeletionPolicy());
         this.similarityService = similarityService;
         Objects.requireNonNull(store, "Store must be provided to the index shard");
         this.engineFactory = engineFactory == null ? new InternalEngineFactory() : engineFactory;
@@ -878,11 +874,11 @@ public org.apache.lucene.util.Version minimumCompatibleVersion() {
 
     /**
      * Creates a new {@link IndexCommit} snapshot form the currently running engine. All resources referenced by this
-     * commit won't be freed until the commit / snapshot is released via {@link #releaseIndexCommit(IndexCommit)}.
+     * commit won't be freed until the commit / snapshot is closed.
      *
      * @param flushFirst <code>true</code> if the index should first be flushed to disk / a low level lucene commit should be executed
      */
-    public IndexCommit acquireIndexCommit(boolean flushFirst) throws EngineException {
+    public Engine.IndexCommitRef acquireIndexCommit(boolean flushFirst) throws EngineException {
         IndexShardState state = this.state; // one time volatile read
         // we allow snapshot on closed index shard, since we want to do one after we close the shard and before we close the engine
         if (state == IndexShardState.STARTED || state == IndexShardState.RELOCATED || state == IndexShardState.CLOSED) {
@@ -893,14 +889,6 @@ public IndexCommit acquireIndexCommit(boolean flushFirst) throws EngineException
     }
 
 
-    /**
-     * Releases a snapshot taken from {@link #acquireIndexCommit(boolean)} this must be called to release the resources
-     * referenced by the given snapshot {@link IndexCommit}.
-     */
-    public void releaseIndexCommit(IndexCommit snapshot) throws IOException {
-        deletionPolicy.release(snapshot);
-    }
-
     /**
      * gets a {@link Store.MetadataSnapshot} for the current directory. This method is safe to call in all lifecycle of the index shard,
      * without having to worry about the current state of the engine and concurrent flushes.
@@ -915,25 +903,24 @@ public void releaseIndexCommit(IndexCommit snapshot) throws IOException {
      * @throws java.nio.file.NoSuchFileException                  if one or more files referenced by a commit are not present.
      */
     public Store.MetadataSnapshot snapshotStoreMetadata() throws IOException {
-        IndexCommit indexCommit = null;
+        Engine.IndexCommitRef indexCommit = null;
         store.incRef();
         try {
+            Engine engine;
             synchronized (mutex) {
                 // if the engine is not running, we can access the store directly, but we need to make sure no one starts
                 // the engine on us. If the engine is running, we can get a snapshot via the deletion policy which is initialized.
                 // That can be done out of mutex, since the engine can be closed half way.
-                Engine engine = getEngineOrNull();
+                engine = getEngineOrNull();
                 if (engine == null) {
                     return store.getMetadata(null, true);
                 }
             }
-            indexCommit = deletionPolicy.snapshot();
-            return store.getMetadata(indexCommit);
+            indexCommit = engine.acquireIndexCommit(false);
+            return store.getMetadata(indexCommit.getIndexCommit());
         } finally {
             store.decRef();
-            if (indexCommit != null) {
-                deletionPolicy.release(indexCommit);
-            }
+            IOUtils.close(indexCommit);
         }
     }
 
@@ -1838,7 +1825,7 @@ private EngineConfig newEngineConfig(EngineConfig.OpenMode openMode) {
         final IndexShardRecoveryPerformer translogRecoveryPerformer = new IndexShardRecoveryPerformer(shardId, mapperService, logger);
         Sort indexSort = indexSortSupplier.get();
         return new EngineConfig(openMode, shardId,
-            threadPool, indexSettings, warmer, store, deletionPolicy, indexSettings.getMergePolicy(),
+            threadPool, indexSettings, warmer, store, indexSettings.getMergePolicy(),
             mapperService.indexAnalyzer(), similarityService.similarity(mapperService), codecService, shardEventListener, translogRecoveryPerformer, indexCache.query(), cachingPolicy, translogConfig,
             IndexingMemoryController.SHARD_INACTIVE_TIME_SETTING.get(indexSettings.getSettings()), refreshListeners, indexSort);
     }

core/src/main/java/org/elasticsearch/index/shard/LocalShardSnapshot.java

@@ -19,7 +19,6 @@
 
 package org.elasticsearch.index.shard;
 
-import org.apache.lucene.index.IndexCommit;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.FilterDirectory;
 import org.apache.lucene.store.IOContext;
@@ -28,6 +27,7 @@
 import org.apache.lucene.store.NoLockFactory;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.index.Index;
+import org.elasticsearch.index.engine.Engine;
 import org.elasticsearch.index.store.Store;
 
 import java.io.Closeable;
@@ -38,7 +38,7 @@
 final class LocalShardSnapshot implements Closeable {
     private final IndexShard shard;
     private final Store store;
-    private final IndexCommit indexCommit;
+    private final Engine.IndexCommitRef indexCommit;
     private final AtomicBoolean closed = new AtomicBoolean(false);
 
     LocalShardSnapshot(IndexShard shard) {
@@ -66,7 +66,7 @@ Directory getSnapshotDirectory() {
         return new FilterDirectory(store.directory()) {
             @Override
             public String[] listAll() throws IOException {
-                Collection<String> fileNames = indexCommit.getFileNames();
+                Collection<String> fileNames = indexCommit.getIndexCommit().getFileNames();
                 final String[] fileNameArray = fileNames.toArray(new String[fileNames.size()]);
                 return fileNameArray;
             }
@@ -115,7 +115,7 @@ public void close() throws IOException {
     public void close() throws IOException {
         if (closed.compareAndSet(false, true)) {
             try {
-                shard.releaseIndexCommit(indexCommit);
+                indexCommit.close();
             } finally {
                 store.decRef();
             }

core/src/main/java/org/elasticsearch/indices/recovery/RecoverySourceHandler.java

@@ -41,6 +41,7 @@
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.util.CancellableThreads;
+import org.elasticsearch.index.engine.Engine;
 import org.elasticsearch.index.engine.RecoveryEngineException;
 import org.elasticsearch.index.seqno.LocalCheckpointTracker;
 import org.elasticsearch.index.seqno.SequenceNumbersService;
@@ -135,20 +136,20 @@ public RecoveryResponse recoverToTarget() throws IOException {
             if (isSequenceNumberBasedRecoveryPossible) {
                 logger.trace("performing sequence numbers based recovery. starting at [{}]", request.startingSeqNo());
             } else {
-                final IndexCommit phase1Snapshot;
+                final Engine.IndexCommitRef phase1Snapshot;
                 try {
                     phase1Snapshot = shard.acquireIndexCommit(false);
                 } catch (final Exception e) {
                     IOUtils.closeWhileHandlingException(translogView);
                     throw new RecoveryEngineException(shard.shardId(), 1, "snapshot failed", e);
                 }
                 try {
-                    phase1(phase1Snapshot, translogView);
+                    phase1(phase1Snapshot.getIndexCommit(), translogView);
                 } catch (final Exception e) {
                     throw new RecoveryEngineException(shard.shardId(), 1, "phase1 failed", e);
                 } finally {
                     try {
-                        shard.releaseIndexCommit(phase1Snapshot);
+                        IOUtils.close(phase1Snapshot);
                     } catch (final IOException ex) {
                         logger.warn("releasing snapshot caused exception", ex);
                     }

core/src/main/java/org/elasticsearch/snapshots/SnapshotShardsService.java

@@ -22,7 +22,6 @@
 import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
 import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.apache.logging.log4j.util.Supplier;
-import org.apache.lucene.index.IndexCommit;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.cluster.ClusterChangedEvent;
 import org.elasticsearch.cluster.ClusterState;
@@ -45,6 +44,7 @@
 import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.concurrent.AbstractRunnable;
+import org.elasticsearch.index.engine.Engine;
 import org.elasticsearch.index.engine.SnapshotFailedEngineException;
 import org.elasticsearch.index.shard.IndexEventListener;
 import org.elasticsearch.index.shard.IndexShard;
@@ -376,17 +376,14 @@ private void snapshot(final IndexShard indexShard, final Snapshot snapshot, fina
 
         try {
             // we flush first to make sure we get the latest writes snapshotted
-            IndexCommit snapshotIndexCommit = indexShard.acquireIndexCommit(true);
-            try {
-                repository.snapshotShard(indexShard, snapshot.getSnapshotId(), indexId, snapshotIndexCommit, snapshotStatus);
+            try (Engine.IndexCommitRef snapshotRef = indexShard.acquireIndexCommit(true)) {
+                repository.snapshotShard(indexShard, snapshot.getSnapshotId(), indexId, snapshotRef.getIndexCommit(), snapshotStatus);
                 if (logger.isDebugEnabled()) {
                     StringBuilder sb = new StringBuilder();
                     sb.append("    index    : version [").append(snapshotStatus.indexVersion()).append("], number_of_files [").append(snapshotStatus.numberOfFiles()).append("] with total_size [").append(new ByteSizeValue(snapshotStatus.totalSize())).append("]\n");
                     logger.debug("snapshot ({}) completed to {}, took [{}]\n{}", snapshot, repository,
                         TimeValue.timeValueMillis(snapshotStatus.time()), sb);
                 }
-            } finally {
-                indexShard.releaseIndexCommit(snapshotIndexCommit);
             }
         } catch (SnapshotFailedEngineException e) {
             throw e;