lucene管理IndexReader和IndexWriter的最佳实践

实例化IndexReader需要加载索引文件，所以实例化它是非常耗资源的。

IndexReader是线程安全的，通常一个索引目录，我们只实例化一个IndexReader就够了。

当索引数据足够大（G的数量级）的时候，一般把索引资源按照某种规则散列到多个文件目录里（如：index-0,index-1,index-2.... 或者 blog,posts....），当然这些文件目录应该放在同一个根目录下---这时，最好的方式就是用一个Pool去维护这些IndexReader：保证一个文件目录只有一个实例，且不同的IndexReader可以根据名字动态的组合。


StandardIndexReaderPool.java

package com.qiu.search.pool.impl;

import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.store.FSDirectory;
import org.springframework.util.Assert;

import com.dukuai.search.exception.PoolException;
import com.dukuai.search.pool.IndexReaderPool;
import com.dukuai.search.util.IndexResourceUtil;
import com.spinn3r.log5j.Logger;

/**
 * {@link IndexReaderPool}的实现类。{@link StandardIndexReaderPool}确保一个目录至多只有一个{@link IndexReader}，它是线程安全的，
 * {@link IndexReader}也是线程安全
 * 
 */

public class StandardIndexReaderPool implements IndexReaderPool {
	private static final Logger LOG = Logger.getLogger(StandardIndexReaderPool.class);
	/** 低版本的IndexReader的存活时间 5s */
	private static final int STALE_INDEXREADER_SURVIVAL_TIME = 5000;

	private String name = null;
	// 索引文件的根目录的路径
	private String indexRootDirectory = null;
	// 索引文件目录名列表，目录名不包含路径
	private List<String> indexDirNameList = null;
	/**
	 * 存放IndexReader的Map，Map里存放的都是已经实例化好的IndexReader
	 */
	private final Map<String, IndexReader> indexReaderMap = new ConcurrentHashMap<String, IndexReader>();
	/**
	 * 待关闭的IndexReader。indexReader.reopen()之后，会产生新的IndexReader。但是旧的IndexReader有可能还被其他线程调用着。
	 * 旧的IndexReader都要放置到staleIndexReadersMap里，5秒之后再释放资源。
	 */
	private final Map<Long, IndexReader> staleIndexReadersMap = new ConcurrentHashMap<Long, IndexReader>();

	@Override
	public void setIndexDirNameList(List<String> indexDirNameList) {
		this.indexDirNameList = indexDirNameList;
	}

	public void init() {
		LOG.info("%s begin initialize", getName());
		for (String indexDirName : indexDirNameList) {
			try {
				IndexReader indexReader = createIndexReader(indexDirName);
				if (indexReader != null)
					indexReaderMap.put(indexDirName, indexReader);
			} catch (IOException e) {// 若初始化时出错，就直接抛错，终止程序再执行下去
				throw new PoolException(e);
			}
		}
		LOG.info("%s initialization complete", getName());
	}

	/**
	 * 根据indexDirPath，返回IndexReader。
	 * 
	 * @param indexDirName 文件目录名
	 * @return IndexReader
	 */
	public IndexReader getIndexReader(String indexDirName) {
		Assert.hasText(indexDirName, "this indexDirName must not be empty");

		IndexReader indexReader = indexReaderMap.get(indexDirName);
		if (indexReader != null)
			return refreshIndexReader(indexDirName, indexReader);

		synchronized (indexReaderMap) {
			if (!indexReaderMap.containsKey(indexDirName)) {
				try {
					indexReader = createIndexReader(indexDirName);
				} catch (CorruptIndexException e) {
					LOG.error("CorruptIndexException while creating IndexReader of %s,the root cause is %s",
							indexDirName, e.getMessage());
				} catch (IOException e) {
					LOG.error("IOException while creating IndexReader of %s,%s", indexDirName, e.getMessage());
				}
				if (indexReader != null)
					indexReaderMap.put(indexDirName, indexReader);
			}
		}
		return indexReaderMap.get(indexDirName);
	}

	/**
	 * 刷新指定的indexReader--加载新的索引数据,若产生新的indexReader，则在indexReaderMap里替换旧的indexReader
	 * 
	 * @param indexDirName
	 * @param indexReader
	 * @return {@link IndexReader}
	 */
	private synchronized IndexReader refreshIndexReader(String indexDirName, IndexReader indexReader) {
		try {
			closeStaleIndexReaders(staleIndexReadersMap);
			LOG.debug("hashCode of indexReader is %s", indexReader.hashCode());
			IndexReader newIndexReader = indexReader.reopen();
			if (newIndexReader != indexReader) {
				// this indexReader are old version
				IndexReader oldIndexReader = indexReader;
				/**
				 * may be this oldIndexReader was invoke by other thread,so put
				 * oldIndexReader to staleIndexReadersMap,closing it after 5s;
				 */
				staleIndexReadersMap.put(System.currentTimeMillis(), oldIndexReader);
				LOG.debug("hashCode of oldIndexReader is %s", oldIndexReader.hashCode());
				// replace old version IndexReader with newIndexReader
				indexReaderMap.put(indexDirName, newIndexReader);
				LOG.debug("hashCode of newIndexReader is %s", newIndexReader.hashCode());
			}
		} catch (Exception e) {
			LOG.error("Exception while getting IndexReader of %s,the root cause is %s", indexDirName, e.getMessage());
		}
		// return newest IndexReader
		return indexReaderMap.get(indexDirName);
	}

	/**
	 * 关闭所有低版本的IndexReaders
	 * 
	 * @param staleIndexReadersMap
	 */
	private void closeStaleIndexReaders(Map<Long, IndexReader> staleIndexReadersMap) {
		Iterator<Entry<Long, IndexReader>> entryIterator = staleIndexReadersMap.entrySet().iterator();
		while (entryIterator.hasNext()) {
			Entry<Long, IndexReader> entry = entryIterator.next();
			if ((System.currentTimeMillis() - entry.getKey()) >= STALE_INDEXREADER_SURVIVAL_TIME) {
				try {
					entry.getValue().close();
					LOG.debug("a stale IndexReader whose hashCode is %s has bean closed", entry.getValue().hashCode());
				} catch (IOException e) {
					LOG.error("IOException while colsing IndexReader,%s", e.getMessage());
				} finally {
					entryIterator.remove();
					LOG.debug("delete a stale IndexReader from pool,hashCode:" + entry.getValue().hashCode());
				}
			}
		}
	}

	public void destroy() {
		Iterator<Entry<String, IndexReader>> iterator = indexReaderMap.entrySet().iterator();
		while (iterator.hasNext()) {
			Entry<String, IndexReader> entry = iterator.next();
			IndexReader indexReader = entry.getValue();
			try {
				indexReader.close();
				indexReader = null;
			} catch (IOException e) {
				LOG.info("IOException while closing IndexReader whose indexDirName is %s", entry.getKey());
			}
		}
		indexReaderMap.clear();
		LOG.info("%s destroyed", getName());
	}
	/**
	 * 根据索引目录名实例化{@link IndexReader},有可能返回null，调用者需要判断返回的{@link IndexReader}是否为null
	 * 
	 * @param indexDirName
	 * @return {@link IndexReader}
	 *         返回indexDirName对应的IndexReader，如果对应的目录不存在就返回null，
	 */
	private IndexReader createIndexReader(String indexDirName) throws CorruptIndexException, IOException {
		File indexFile = new File(IndexResourceUtil.getDirPath(indexRootDirectory, indexDirName));
		if (IndexResourceUtil.isEmptyIndexDir(indexFile)) {
			LOG.warn("%s is empty,no index resource", indexDirName);
			return null;
		}
		if (indexFile.exists() && indexFile.isDirectory()) {// 判断索引目录是否存在。
			return IndexReader.open(FSDirectory.getDirectory(indexFile));
		}
		return null;
	}

	public int size() {
		return indexReaderMap.size();
	}

	@Override
	public String toString() {
		return (new ToStringBuilder(this).append("name", getName()).append("indexRootDirectory", indexRootDirectory)
				.append("size", size()).append("indexReader Set", indexReaderMap.keySet())).toString();
	}

	public String getName() {
		return name;
	}

	/** spring inject */
	public void setIndexRootDirectory(String indexRootDirectory) {
		this.indexRootDirectory = indexRootDirectory;
	}
	public void setName(String name) {
		this.name = name;
	}

}

IndexWriter也需要Pool来管理

StandardIndexWriterPool.java

package com.dukuai.search.pool.impl;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexWriter;

import com.dukuai.search.exception.PoolException;
import com.dukuai.search.pool.IndexWriterPool;
import com.dukuai.search.util.IndexResourceUtil;
import com.dukuai.search.util.MetisUtil;
import com.spinn3r.log5j.Logger;

/**
 * <code>IndexWriterPool</code>的实现类。<code>StandardIndexWriterPool</code>是线程安全的


public class StandardIndexWriterPool implements IndexWriterPool {
	private static final Logger LOG = Logger.getLogger();
	/**
	 * 索引优化后文件段的数量，数量越大，优化效率月到
	 */
	private static final int DEFAULT_MAX_NUM_SEGMENTS = 2;
    
	private String indexRootDirectory = null;
	private String name = null;
	/**
	 * 索引优化后块的数量，数字越大优化速度越快、优化效果越不显著。
	 */
	private int maxNumSegments = DEFAULT_MAX_NUM_SEGMENTS;
	/**
	 * 存放IndexWriter的map
	 */
	private Map<String, IndexWriter> indexWriterMap = new ConcurrentHashMap<String, IndexWriter>();

	private List<String> indexDirNameList = null;

	@Override
	public void setIndexDirNameList(List<String> indexDirNameList) {
		this.indexDirNameList = indexDirNameList;
	}
	/**
	 * <code>StandardIndexWriterPool</code>的初始化，预加载<code>IndexWriter</code>。
	 */
	public void init() {
		LOG.info("%s begin initialize", getName());
		synchronized (indexWriterMap) {
			for (String indexDirName : indexDirNameList) {
				indexWriterMap.put(indexDirName, createIndexWriter(indexDirName));
			}
		}
		LOG.info("%s initialization complete", getName());
	}

	/**
	 * 返回一个indexWriter,indexWriter是线程安全的,允许多个线程同时使用IndexWriter。但一个索引目录只能初始化一个IndexWriter
	 * 
	 * @param indexDirName
	 * @return IndexWriter
	 */
	public IndexWriter getIndexWriter(String indexDirName) {
		if (!indexWriterMap.containsKey(indexDirName)) {
			synchronized (indexWriterMap) {
				if (!indexWriterMap.containsKey(indexDirName)) {
					indexWriterMap.put(indexDirName, createIndexWriter(indexDirName));
					LOG.info("added a new IndexWriter whose name is %s to pool,the pool size:%s", indexDirName, size());
				}
			}
		}
		return indexWriterMap.get(indexDirName);
	}

	/**
	 * 创建一个新的IndexWriter，不允许多个线程同时调用，因为方法是私有的，能确保不会同时被调用，所以就免去锁了。
	 * 
	 * @param indexDirName
	 * @return {@link IndexWriter}
	 */
	private IndexWriter createIndexWriter(String indexDirName) {
		final String indexDirPath = getIndexDirPath(indexDirName);
		boolean create = IndexResourceUtil.isEmptyIndexDir(indexDirPath);
		try {
			return new IndexWriter(indexDirPath, new StandardAnalyzer(), create, IndexWriter.MaxFieldLength.LIMITED);
		} catch (Exception e) {
			throw new PoolException(e.getMessage());
		}
	}
	/**
	 * 提交索引，只有提交的索引才能被检索的到。 见{@link IndexWriter#commit()}
	 */
	public void commit() {
		LOG.info("begin to commit all IndexWiters of pool,the pool size:%s", size());
		synchronized (indexWriterMap) {
			Iterator<Entry<String, IndexWriter>> iterator = indexWriterMap.entrySet().iterator();
			while (iterator.hasNext()) {
				Entry<String, IndexWriter> entry = iterator.next();
				IndexWriter indexWriter = entry.getValue();
				try {
					indexWriter.commit();
				} catch (Exception e) {
					LOG.error("exception while commiting pending updates,indexDir:%s,exception:%s", entry.getKey(), e
							.getMessage());
					destoryIndexWriter(iterator, indexWriter);
				}
			}
		}
		LOG.info("%s IndexWiters had committed pending updates", size());
	}

	/**
	 * 优化索引，提升检索速度。另注意事项见{@link IndexWriter#optimize}
	 */
	public void optimize() {
		LOG.info("begin to optimize at %s", MetisUtil.getCurrentDisplayFormatTime());
		synchronized (indexWriterMap) {
			Iterator<Entry<String, IndexWriter>> iterator = indexWriterMap.entrySet().iterator();
			while (iterator.hasNext()) {
				Entry<String, IndexWriter> entry = iterator.next();
				IndexWriter indexWriter = entry.getValue();
				try {
					indexWriter.commit();
					indexWriter.optimize(maxNumSegments);
				} catch (Exception e) {
					LOG.error("Exception while optimizing %s,the root cause:%s", entry.getKey(), e.getMessage());
					destoryIndexWriter(iterator, indexWriter);
				}
			}
		}
		LOG.info("end optimize at %s", MetisUtil.getCurrentDisplayFormatTime());
	}

	/**
	 * 重新加载所有的{@link IndexWriter},{@link IndexWriter}不会及时释放哪些在创建索引过程中产生的索引文件碎片，哪怕哪些索引文件已经消失。
	 * {@link #reload()}就是为了释放哪些文件句柄，防止进程持有过多的文件句柄。
	 */
	public void reload() {
		LOG.info("begin to reload %s at %s", name, MetisUtil.getCurrentDisplayFormatTime());
		// 需要重新加载的索引目录列表
		List<String> indexDirNameList = new ArrayList<String>();
		synchronized (indexWriterMap) {
			Iterator<Entry<String, IndexWriter>> iterator = indexWriterMap.entrySet().iterator();
			while (iterator.hasNext()) {
				Entry<String, IndexWriter> entry = iterator.next();
				indexDirNameList.add(entry.getKey());
				IndexWriter indexWriter = entry.getValue();
				try {
					indexWriter.commit();
				} catch (Exception e) {
					LOG.error("Exception while commiting %s,the root cause:%s", entry.getKey(), e.getMessage());
				} finally {
					destoryIndexWriter(iterator, indexWriter);
				}
			}

			for (String indexDirName : indexDirNameList) {
				indexWriterMap.put(indexDirName, createIndexWriter(indexDirName));
			}
		}
		LOG.info("%s reload end at %s", name, MetisUtil.getCurrentDisplayFormatTime());
	}
	/**
	 * 销毁指定的{@link IndexWriter}
	 */
	private void destoryIndexWriter(Iterator<Entry<String, IndexWriter>> iterator, IndexWriter indexWriter) {
		try {
			indexWriter.close();
		} catch (CorruptIndexException e) {
			LOG.error("CorruptIndexException while closing indexWriter,the root cause:%s", e.getMessage());
		} catch (IOException e) {
			LOG.error("IOException while closing indexWriter,the root cause:%s", e.getMessage());
		}
		iterator.remove();
		LOG.info("destory a indexWriter,current pool's size:%s", size());
	}
	/**
	 * 销毁{@link StandardIndexWriterPool}，释放持有的资源。
	 */
	public void destroy() {
		synchronized (indexWriterMap) {
			Iterator<Entry<String, IndexWriter>> iterator = indexWriterMap.entrySet().iterator();
			while (iterator.hasNext()) {
				Entry<String, IndexWriter> entry = iterator.next();
				IndexWriter indexWriter = entry.getValue();
				try {
					indexWriter.commit();
					indexWriter.close();
				} catch (Exception e) {
					LOG.error("Exception while closing %s,the root cause:%s", entry.getKey(), e.getMessage());
					destoryIndexWriter(iterator, indexWriter);
				}
			}
			indexWriterMap = null;
			LOG.info("%s destoryed", getName());
		}
	}

	private String getIndexDirPath(String indexDirName) {
		return (new StringBuffer(indexRootDirectory).append(File.separatorChar).append(indexDirName)).toString();
	}

	public int size() {
		return this.indexWriterMap.size();
	}

	public String getName() {
		return name;
	}

	@Override
	public String toString() {
		ToStringBuilder builder = new ToStringBuilder(this);
		builder.append("name", this.name);
		builder.append("indexRootDirectory", this.indexRootDirectory);
		builder.append("size", this.size());
		builder.append("IndexWriter Set", indexWriterMap.keySet());
		return builder.toString();
	}

	/** spring inject */
	public void setName(String name) {
		this.name = name;
	}
	public void setIndexRootDirectory(String indexRootDirectory) {
		this.indexRootDirectory = indexRootDirectory;
	}

	public void setMaxNumSegments(int maxNumSegments) {
		this.maxNumSegments = maxNumSegments;
	}
}