org.apache.lucene.index.UpgradeIndexMergePolicy.java Source code

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Here is the source code for org.apache.lucene.index.UpgradeIndexMergePolicy.java

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/*
 * 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.
 */
package org.apache.lucene.index;

import org.apache.lucene.util.Version;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.HashMap;

/** This {@link MergePolicy} is used for upgrading all existing segments of
  * an index when calling {@link IndexWriter#forceMerge(int)}.
  * All other methods delegate to the base {@code MergePolicy} given to the constructor.
  * This allows for an as-cheap-as possible upgrade of an older index by only upgrading segments that
  * are created by previous Lucene versions. forceMerge does no longer really merge;
  * it is just used to "forceMerge" older segment versions away.
  * <p>In general one would use {@link IndexUpgrader}, but for a fully customizeable upgrade,
  * you can use this like any other {@code MergePolicy} and call {@link IndexWriter#forceMerge(int)}:
  * <pre class="prettyprint lang-java">
  *  IndexWriterConfig iwc = new IndexWriterConfig(Version.LUCENE_XX, new KeywordAnalyzer());
  *  iwc.setMergePolicy(new UpgradeIndexMergePolicy(iwc.getMergePolicy()));
  *  IndexWriter w = new IndexWriter(dir, iwc);
  *  w.forceMerge(1);
  *  w.close();
  * </pre>
  * <p><b>Warning:</b> This merge policy may reorder documents if the index was partially
  * upgraded before calling forceMerge (e.g., documents were added). If your application relies
  * on &quot;monotonicity&quot; of doc IDs (which means that the order in which the documents
  * were added to the index is preserved), do a forceMerge(1) instead. Please note, the
  * delegate {@code MergePolicy} may also reorder documents.
  * @lucene.experimental
  * @see IndexUpgrader
  */
public class UpgradeIndexMergePolicy extends FilterMergePolicy {

    /** Wrap the given {@link MergePolicy} and intercept forceMerge requests to
     * only upgrade segments written with previous Lucene versions. */
    public UpgradeIndexMergePolicy(MergePolicy in) {
        super(in);
    }

    /** Returns if the given segment should be upgraded. The default implementation
     * will return {@code !Version.LATEST.equals(si.getVersion())},
     * so all segments created with a different version number than this Lucene version will
     * get upgraded.
     */
    protected boolean shouldUpgradeSegment(SegmentCommitInfo si) {
        return !Version.LATEST.equals(si.info.getVersion());
    }

    @Override
    public MergeSpecification findMerges(MergeTrigger mergeTrigger, SegmentInfos segmentInfos,
            MergeContext mergeContext) throws IOException {
        return in.findMerges(null, segmentInfos, mergeContext);
    }

    @Override
    public MergeSpecification findForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount,
            Map<SegmentCommitInfo, Boolean> segmentsToMerge, MergeContext mergeContext) throws IOException {
        // first find all old segments
        final Map<SegmentCommitInfo, Boolean> oldSegments = new HashMap<>();
        for (final SegmentCommitInfo si : segmentInfos) {
            final Boolean v = segmentsToMerge.get(si);
            if (v != null && shouldUpgradeSegment(si)) {
                oldSegments.put(si, v);
            }
        }

        if (verbose(mergeContext)) {
            message("findForcedMerges: segmentsToUpgrade=" + oldSegments, mergeContext);
        }

        if (oldSegments.isEmpty())
            return null;

        MergeSpecification spec = in.findForcedMerges(segmentInfos, maxSegmentCount, oldSegments, mergeContext);

        if (spec != null) {
            // remove all segments that are in merge specification from oldSegments,
            // the resulting set contains all segments that are left over
            // and will be merged to one additional segment:
            for (final OneMerge om : spec.merges) {
                oldSegments.keySet().removeAll(om.segments);
            }
        }

        if (!oldSegments.isEmpty()) {
            if (verbose(mergeContext)) {
                message("findForcedMerges: " + in.getClass().getSimpleName()
                        + " does not want to merge all old segments, merge remaining ones into new segment: "
                        + oldSegments, mergeContext);
            }
            final List<SegmentCommitInfo> newInfos = new ArrayList<>();
            for (final SegmentCommitInfo si : segmentInfos) {
                if (oldSegments.containsKey(si)) {
                    newInfos.add(si);
                }
            }
            // add the final merge
            if (spec == null) {
                spec = new MergeSpecification();
            }
            spec.add(new OneMerge(newInfos));
        }

        return spec;
    }

}