001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hdfs.server.datanode;
019
020/**
021 * The caching strategy we should use for an HDFS read or write operation.
022 */
023public class CachingStrategy {
024  private final Boolean dropBehind; // null = use server defaults
025  private final Long readahead; // null = use server defaults
026  
027  public static CachingStrategy newDefaultStrategy() {
028    return new CachingStrategy(null, null);
029  }
030
031  public static CachingStrategy newDropBehind() {
032    return new CachingStrategy(true, null);
033  }
034
035  public static class Builder {
036    private Boolean dropBehind;
037    private Long readahead;
038
039    public Builder(CachingStrategy prev) {
040      this.dropBehind = prev.dropBehind;
041      this.readahead = prev.readahead;
042    }
043
044    public Builder setDropBehind(Boolean dropBehind) {
045      this.dropBehind = dropBehind;
046      return this;
047    }
048
049    public Builder setReadahead(Long readahead) {
050      this.readahead = readahead;
051      return this;
052    }
053
054    public CachingStrategy build() {
055      return new CachingStrategy(dropBehind, readahead);
056    }
057  }
058
059  public CachingStrategy(Boolean dropBehind, Long readahead) {
060    this.dropBehind = dropBehind;
061    this.readahead = readahead;
062  }
063
064  public Boolean getDropBehind() {
065    return dropBehind;
066  }
067  
068  public Long getReadahead() {
069    return readahead;
070  }
071
072  public String toString() {
073    return "CachingStrategy(dropBehind=" + dropBehind +
074        ", readahead=" + readahead + ")";
075  }
076}