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

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Here is the source code for org.apache.lucene.index.MergeScheduler.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.Closeable;
import java.io.IOException;

import org.apache.lucene.index.MergePolicy.OneMerge;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RateLimitedIndexOutput;
import org.apache.lucene.util.InfoStream;

/** <p>Expert: {@link IndexWriter} uses an instance
 *  implementing this interface to execute the merges
 *  selected by a {@link MergePolicy}.  The default
 *  MergeScheduler is {@link ConcurrentMergeScheduler}.</p>
 * @lucene.experimental
*/
public abstract class MergeScheduler implements Closeable {

    /** Sole constructor. (For invocation by subclass 
     *  constructors, typically implicit.) */
    protected MergeScheduler() {
    }

    /** Run the merges provided by {@link IndexWriter#getNextMerge()}.
     * @param writer the {@link IndexWriter} to obtain the merges from.
     * @param trigger the {@link MergeTrigger} that caused this merge to happen
     * @param newMergesFound <code>true</code> iff any new merges were found by the caller otherwise <code>false</code>
     * */
    public abstract void merge(IndexWriter writer, MergeTrigger trigger, boolean newMergesFound) throws IOException;

    /** 
     * Wraps the incoming {@link Directory} so that we can merge-throttle it
     * using {@link RateLimitedIndexOutput}. 
     */
    public Directory wrapForMerge(OneMerge merge, Directory in) {
        // A no-op by default.
        return in;
    }

    /** Close this MergeScheduler. */
    @Override
    public abstract void close() throws IOException;

    /** For messages about merge scheduling */
    protected InfoStream infoStream;

    /** IndexWriter calls this on init. */
    final void setInfoStream(InfoStream infoStream) {
        this.infoStream = infoStream;
    }

    /**
     * Returns true if infoStream messages are enabled. This method is usually used in
     * conjunction with {@link #message(String)}:
     * 
     * <pre class="prettyprint">
     * if (verbose()) {
     *   message(&quot;your message&quot;);
     * }
     * </pre>
     */
    protected boolean verbose() {
        return infoStream != null && infoStream.isEnabled("MS");
    }

    /**
     * Outputs the given message - this method assumes {@link #verbose()} was
     * called and returned true.
     */
    protected void message(String message) {
        infoStream.message("MS", message);
    }
}