org.neo4j.kernel.api.impl.index.backup.LuceneIndexSnapshotFileIterator.java Source code

Introduction

Here is the source code for org.neo4j.kernel.api.impl.index.backup.LuceneIndexSnapshotFileIterator.java

Source

/*
 * Copyright (c) 2002-2016 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.kernel.api.impl.index.backup;

import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexCommit;
import org.apache.lucene.index.IndexDeletionPolicy;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.SegmentInfos;
import org.apache.lucene.index.SnapshotDeletionPolicy;
import org.apache.lucene.store.Directory;

import java.io.File;
import java.io.IOException;
import java.util.Iterator;

import org.neo4j.graphdb.ResourceIterator;
import org.neo4j.helpers.collection.PrefetchingIterator;

import static org.neo4j.helpers.collection.Iterators.emptyIterator;

/**
 * Iterator over Lucene index files for a particular {@link IndexCommit snapshot}.
 * Applicable only to a single Lucene index partition.
 * Internally uses {@link SnapshotDeletionPolicy#snapshot()} to create an {@link IndexCommit} that represents
 * consistent state of the index for a particular point in time.
 *
 * Turns to be an empty iterator if index does not have any commits yet.
 */
public class LuceneIndexSnapshotFileIterator extends PrefetchingIterator<File> implements ResourceIterator<File> {
    private final File indexDirectory;
    private final SnapshotDeletionPolicy snapshotDeletionPolicy;
    private final Iterator<String> fileNames;
    private final IndexCommit snapshot;

    public static ResourceIterator<File> forIndex(File indexFolder, IndexWriter indexWriter) throws IOException {
        IndexDeletionPolicy deletionPolicy = indexWriter.getConfig().getIndexDeletionPolicy();
        if (deletionPolicy instanceof SnapshotDeletionPolicy) {
            SnapshotDeletionPolicy policy = (SnapshotDeletionPolicy) deletionPolicy;
            return hasCommits(indexWriter) ? new LuceneIndexSnapshotFileIterator(indexFolder, policy)
                    : emptyIterator();
        } else {
            throw new UnsupportedIndexDeletionPolicy("Can't perform index snapshot with specified index deleiton "
                    + "policy: " + deletionPolicy.getClass().getName() + ". " + "Only "
                    + SnapshotDeletionPolicy.class.getName() + " is " + "supported");
        }
    }

    private LuceneIndexSnapshotFileIterator(File indexDirectory, SnapshotDeletionPolicy snapshotDeletionPolicy)
            throws IOException {
        this.snapshot = snapshotDeletionPolicy.snapshot();
        this.indexDirectory = indexDirectory;
        this.snapshotDeletionPolicy = snapshotDeletionPolicy;
        this.fileNames = snapshot.getFileNames().iterator();
    }

    @Override
    protected File fetchNextOrNull() {
        if (!fileNames.hasNext()) {
            return null;
        }
        return new File(indexDirectory, fileNames.next());
    }

    @Override
    public void close() {
        try {
            snapshotDeletionPolicy.release(snapshot);
        } catch (IOException e) {
            throw new SnapshotReleaseException(
                    "Unable to release lucene index snapshot for index in: " + indexDirectory, e);
        }
    }

    private static boolean hasCommits(IndexWriter indexWriter) throws IOException {
        Directory directory = indexWriter.getDirectory();
        return DirectoryReader.indexExists(directory) && SegmentInfos.readLatestCommit(directory) != null;
    }

}