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

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Here is the source code for org.apache.lucene.index.LogByteSizeMergePolicy.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 java.io.IOException;

/** This is a {@link LogMergePolicy} that measures size of a
 *  segment as the total byte size of the segment's files. */
public class LogByteSizeMergePolicy extends LogMergePolicy {

    /** Default minimum segment size.  @see setMinMergeMB */
    public static final double DEFAULT_MIN_MERGE_MB = 1.6;

    /** Default maximum segment size.  A segment of this size
     *  or larger will never be merged.  @see setMaxMergeMB */
    public static final double DEFAULT_MAX_MERGE_MB = 2048;

    /** Default maximum segment size.  A segment of this size
     *  or larger will never be merged during forceMerge.  @see setMaxMergeMBForForceMerge */
    public static final double DEFAULT_MAX_MERGE_MB_FOR_FORCED_MERGE = Long.MAX_VALUE;

    /** Sole constructor, setting all settings to their
     *  defaults. */
    public LogByteSizeMergePolicy() {
        minMergeSize = (long) (DEFAULT_MIN_MERGE_MB * 1024 * 1024);
        maxMergeSize = (long) (DEFAULT_MAX_MERGE_MB * 1024 * 1024);
        // NOTE: in Java, if you cast a too-large double to long, as we are doing here, then it becomes Long.MAX_VALUE
        maxMergeSizeForForcedMerge = (long) (DEFAULT_MAX_MERGE_MB_FOR_FORCED_MERGE * 1024 * 1024);
    }

    @Override
    protected long size(SegmentCommitInfo info, MergeContext mergeContext) throws IOException {
        return sizeBytes(info, mergeContext);
    }

    /** <p>Determines the largest segment (measured by total
     *  byte size of the segment's files, in MB) that may be
     *  merged with other segments.  Small values (e.g., less
     *  than 50 MB) are best for interactive indexing, as this
     *  limits the length of pauses while indexing to a few
     *  seconds.  Larger values are best for batched indexing
     *  and speedier searches.</p>
     *
     *  <p>Note that {@link #setMaxMergeDocs} is also
     *  used to check whether a segment is too large for
     *  merging (it's either or).</p>*/
    public void setMaxMergeMB(double mb) {
        maxMergeSize = (long) (mb * 1024 * 1024);
    }

    /** Returns the largest segment (measured by total byte
     *  size of the segment's files, in MB) that may be merged
     *  with other segments.
     *  @see #setMaxMergeMB */
    public double getMaxMergeMB() {
        return ((double) maxMergeSize) / 1024 / 1024;
    }

    /** <p>Determines the largest segment (measured by total
     *  byte size of the segment's files, in MB) that may be
     *  merged with other segments during forceMerge. Setting
     *  it low will leave the index with more than 1 segment,
     *  even if {@link IndexWriter#forceMerge} is called.*/
    public void setMaxMergeMBForForcedMerge(double mb) {
        maxMergeSizeForForcedMerge = (long) (mb * 1024 * 1024);
    }

    /** Returns the largest segment (measured by total byte
     *  size of the segment's files, in MB) that may be merged
     *  with other segments during forceMerge.
     *  @see #setMaxMergeMBForForcedMerge */
    public double getMaxMergeMBForForcedMerge() {
        return ((double) maxMergeSizeForForcedMerge) / 1024 / 1024;
    }

    /** Sets the minimum size for the lowest level segments.
     * Any segments below this size are considered to be on
     * the same level (even if they vary drastically in size)
     * and will be merged whenever there are mergeFactor of
     * them.  This effectively truncates the "long tail" of
     * small segments that would otherwise be created into a
     * single level.  If you set this too large, it could
     * greatly increase the merging cost during indexing (if
     * you flush many small segments). */
    public void setMinMergeMB(double mb) {
        minMergeSize = (long) (mb * 1024 * 1024);
    }

    /** Get the minimum size for a segment to remain
     *  un-merged.
     *  @see #setMinMergeMB **/
    public double getMinMergeMB() {
        return ((double) minMergeSize) / 1024 / 1024;
    }
}