--- /dev/null
+package org.apache.lucene.index;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with this
+ * work for additional information regarding copyright ownership. The ASF
+ * 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.
+ */
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import org.apache.lucene.document.Document;
+import org.apache.lucene.document.Field;
+import org.apache.lucene.document.Fieldable;
+import org.apache.lucene.document.Field.Index;
+import org.apache.lucene.document.Field.Store;
+import org.apache.lucene.index.IndexWriterConfig.OpenMode;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.LockObtainFailedException;
+import org.apache.lucene.util.Version;
+
+/**
+ * A {@link SnapshotDeletionPolicy} which adds a persistence layer so that
+ * snapshots can be maintained across the life of an application. The snapshots
+ * are persisted in a {@link Directory} and are committed as soon as
+ * {@link #snapshot(String)} or {@link #release(String)} is called.
+ * <p>
+ * <b>NOTE:</b> this class receives a {@link Directory} to persist the data into
+ * a Lucene index. It is highly recommended to use a dedicated directory (and on
+ * stable storage as well) for persisting the snapshots' information, and not
+ * reuse the content index directory, or otherwise conflicts and index
+ * corruptions will occur.
+ * <p>
+ * <b>NOTE:</b> you should call {@link #close()} when you're done using this
+ * class for safetyness (it will close the {@link IndexWriter} instance used).
+ */
+public class PersistentSnapshotDeletionPolicy extends SnapshotDeletionPolicy {
+
+ // Used to validate that the given directory includes just one document w/ the
+ // given ID field. Otherwise, it's not a valid Directory for snapshotting.
+ private static final String SNAPSHOTS_ID = "$SNAPSHOTS_DOC$";
+
+ // The index writer which maintains the snapshots metadata
+ private final IndexWriter writer;
+
+ /**
+ * Reads the snapshots information from the given {@link Directory}. This
+ * method can be used if the snapshots information is needed, however you
+ * cannot instantiate the deletion policy (because e.g., some other process
+ * keeps a lock on the snapshots directory).
+ */
+ public static Map<String, String> readSnapshotsInfo(Directory dir) throws IOException {
+ IndexReader r = IndexReader.open(dir, true);
+ Map<String, String> snapshots = new HashMap<String, String>();
+ try {
+ int numDocs = r.numDocs();
+ // index is allowed to have exactly one document or 0.
+ if (numDocs == 1) {
+ Document doc = r.document(r.maxDoc() - 1);
+ Field sid = doc.getField(SNAPSHOTS_ID);
+ if (sid == null) {
+ throw new IllegalStateException("directory is not a valid snapshots store!");
+ }
+ doc.removeField(SNAPSHOTS_ID);
+ for (Fieldable f : doc.getFields()) {
+ snapshots.put(f.name(), f.stringValue());
+ }
+ } else if (numDocs != 0) {
+ throw new IllegalStateException(
+ "should be at most 1 document in the snapshots directory: " + numDocs);
+ }
+ } finally {
+ r.close();
+ }
+ return snapshots;
+ }
+
+ /**
+ * {@link PersistentSnapshotDeletionPolicy} wraps another
+ * {@link IndexDeletionPolicy} to enable flexible snapshotting.
+ *
+ * @param primary
+ * the {@link IndexDeletionPolicy} that is used on non-snapshotted
+ * commits. Snapshotted commits, by definition, are not deleted until
+ * explicitly released via {@link #release(String)}.
+ * @param dir
+ * the {@link Directory} which will be used to persist the snapshots
+ * information.
+ * @param mode
+ * specifies whether a new index should be created, deleting all
+ * existing snapshots information (immediately), or open an existing
+ * index, initializing the class with the snapshots information.
+ * @param matchVersion
+ * specifies the {@link Version} that should be used when opening the
+ * IndexWriter.
+ */
+ public PersistentSnapshotDeletionPolicy(IndexDeletionPolicy primary,
+ Directory dir, OpenMode mode, Version matchVersion)
+ throws CorruptIndexException, LockObtainFailedException, IOException {
+ super(primary, null);
+
+ // Initialize the index writer over the snapshot directory.
+ writer = new IndexWriter(dir, new IndexWriterConfig(matchVersion, null).setOpenMode(mode));
+ if (mode != OpenMode.APPEND) {
+ // IndexWriter no longer creates a first commit on an empty Directory. So
+ // if we were asked to CREATE*, call commit() just to be sure. If the
+ // index contains information and mode is CREATE_OR_APPEND, it's a no-op.
+ writer.commit();
+ }
+
+ try {
+ // Initializes the snapshots information. This code should basically run
+ // only if mode != CREATE, but if it is, it's no harm as we only open the
+ // reader once and immediately close it.
+ for (Entry<String, String> e : readSnapshotsInfo(dir).entrySet()) {
+ registerSnapshotInfo(e.getKey(), e.getValue(), null);
+ }
+ } catch (RuntimeException e) {
+ writer.close(); // don't leave any open file handles
+ throw e;
+ } catch (IOException e) {
+ writer.close(); // don't leave any open file handles
+ throw e;
+ }
+ }
+
+ @Override
+ public synchronized void onInit(List<? extends IndexCommit> commits)
+ throws IOException {
+ // super.onInit() needs to be called first to ensure that initialization
+ // behaves as expected. The superclass, SnapshotDeletionPolicy, ensures
+ // that any snapshot IDs with empty IndexCommits are released. Since this
+ // happens, this class needs to persist these changes.
+ super.onInit(commits);
+ persistSnapshotInfos(null, null);
+ }
+
+ /**
+ * Snapshots the last commit using the given ID. Once this method returns, the
+ * snapshot information is persisted in the directory.
+ *
+ * @see SnapshotDeletionPolicy#snapshot(String)
+ */
+ @Override
+ public synchronized IndexCommit snapshot(String id) throws IOException {
+ checkSnapshotted(id);
+ if (SNAPSHOTS_ID.equals(id)) {
+ throw new IllegalArgumentException(id + " is reserved and cannot be used as a snapshot id");
+ }
+ persistSnapshotInfos(id, lastCommit.getSegmentsFileName());
+ return super.snapshot(id);
+ }
+
+ /**
+ * Deletes a snapshotted commit by ID. Once this method returns, the snapshot
+ * information is committed to the directory.
+ *
+ * @see SnapshotDeletionPolicy#release(String)
+ */
+ @Override
+ public synchronized void release(String id) throws IOException {
+ super.release(id);
+ persistSnapshotInfos(null, null);
+ }
+
+ /** Closes the index which writes the snapshots to the directory. */
+ public void close() throws CorruptIndexException, IOException {
+ writer.close();
+ }
+
+ /**
+ * Persists all snapshots information. If the given id and segment are not
+ * null, it persists their information as well.
+ */
+ private void persistSnapshotInfos(String id, String segment) throws IOException {
+ writer.deleteAll();
+ Document d = new Document();
+ d.add(new Field(SNAPSHOTS_ID, "", Store.YES, Index.NO));
+ for (Entry<String, String> e : super.getSnapshots().entrySet()) {
+ d.add(new Field(e.getKey(), e.getValue(), Store.YES, Index.NO));
+ }
+ if (id != null) {
+ d.add(new Field(id, segment, Store.YES, Index.NO));
+ }
+ writer.addDocument(d);
+ writer.commit();
+ }
+
+}
fnp / pylucene.git / blobdiff