/**
    * 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.regionserver;
  
  import java.io.IOException;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.util.ReflectionUtils;
  
  /**
   * The class that creates a flush policy from a conf and HTableDescriptor.
   * <p>
   * The default flush policy is {@link FlushLargeStoresPolicy}. And for 0.98, the default flush
   * policy is {@link FlushAllStoresPolicy}.
   */
  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.CONFIG)
  public class FlushPolicyFactory {
  
    private static final Log LOG = LogFactory.getLog(FlushPolicyFactory.class);
  
    public static final String HBASE_FLUSH_POLICY_KEY = "hbase.regionserver.flush.policy";
  
    private static final Class<? extends FlushPolicy> DEFAULT_FLUSH_POLICY_CLASS =
        FlushLargeStoresPolicy.class;
  
    /**
     * Create the FlushPolicy configured for the given table.
     */
    public static FlushPolicy create(HRegion region, Configuration conf) throws IOException {
      Class<? extends FlushPolicy> clazz = getFlushPolicyClass(region.getTableDesc(), conf);
      FlushPolicy policy = ReflectionUtils.newInstance(clazz, conf);
      policy.configureForRegion(region);
      return policy;
    }
  
    /**
     * Get FlushPolicy class for the given table.
     */
    public static Class<? extends FlushPolicy> getFlushPolicyClass(HTableDescriptor htd,
        Configuration conf) throws IOException {
      String className = htd.getFlushPolicyClassName();
      if (className == null) {
        className = conf.get(HBASE_FLUSH_POLICY_KEY, DEFAULT_FLUSH_POLICY_CLASS.getName());
      }
      try {
        Class<? extends FlushPolicy> clazz = Class.forName(className).asSubclass(FlushPolicy.class);
        return clazz;
      } catch (Exception e) {
        LOG.warn(
          "Unable to load configured flush policy '" + className + "' for table '"
              + htd.getTableName() + "', load default flush policy "
              + DEFAULT_FLUSH_POLICY_CLASS.getName() + " instead", e);
        return DEFAULT_FLUSH_POLICY_CLASS;
      }
    }
  }