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HBase is the <a href="http://hadoop.apache.org"&rt;Hadoop</a&rt; database. Use it when you need random, realtime read/write access to your Big Data. This project's goal is the hosting of very large tables -- billions of rows X millions of columns -- atop clusters of commodity hardware.

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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.hadoop.hbase.io;

import java.io.IOException;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.util.FSUtils;

/**
 * HLogLink describes a link to a WAL.
 *
 * An hlog can be in /hbase/.logs//
 * or it can be in /hbase/.oldlogs/
 *
 * The link checks first in the original path,
 * if it is not present it fallbacks to the archived path.
 */
@InterfaceAudience.Private
public class HLogLink extends FileLink {
  /**
   * @param conf {@link Configuration} from which to extract specific archive locations
   * @param serverName Region Server owner of the log
   * @param logName WAL file name
   * @throws IOException on unexpected error.
   */
  public HLogLink(final Configuration conf,
      final String serverName, final String logName) throws IOException {
    this(FSUtils.getRootDir(conf), serverName, logName);
  }

  /**
   * @param rootDir Path to the root directory where hbase files are stored
   * @param serverName Region Server owner of the log
   * @param logName WAL file name
   */
  public HLogLink(final Path rootDir, final String serverName, final String logName) {
    final Path oldLogDir = new Path(rootDir, HConstants.HREGION_OLDLOGDIR_NAME);
    final Path logDir = new Path(new Path(rootDir, HConstants.HREGION_LOGDIR_NAME), serverName);
    setLocations(new Path(logDir, logName), new Path(oldLogDir, logName));
  }

  /**
   * @param originPath Path to the wal in the log directory
   * @param archivePath Path to the wal in the archived log directory
   */
  public HLogLink(final Path originPath, final Path archivePath) {
    setLocations(originPath, archivePath);
  }
}