com.alibaba.wasp.fserver.EntityGroupSplitPolicy.java Source code

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Here is the source code for com.alibaba.wasp.fserver.EntityGroupSplitPolicy.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 com.alibaba.wasp.fserver;

import com.alibaba.wasp.FConstants;
import com.alibaba.wasp.meta.FTable;
import com.google.common.base.Preconditions;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.util.ReflectionUtils;

import java.io.IOException;

/**
 * A split policy determines when a entityGroup should be split.
 * 
 */
public abstract class EntityGroupSplitPolicy extends Configured {
    private static final Class<? extends EntityGroupSplitPolicy> DEFAULT_SPLIT_POLICY_CLASS = DefaultEntityGroupSplitPolicy.class;

    /**
     * The entityGroup configured for this split policy.
     */
    protected EntityGroup entityGroup;

    /**
     * Upon construction, this method will be called with the entityGroup to be
     * governed. It will be called once and only once.
     */
    protected void configureForEntityGroup(EntityGroup entityGroup) {
        Preconditions.checkState(this.entityGroup == null, "Policy already configured for entityGroup {}",
                this.entityGroup);

        this.entityGroup = entityGroup;
    }

    /**
     * @return the key at which the entityGroup should be split, or null if it cannot
     *         be split. This will only be called if shouldSplit previously
     *         returned true.
     */
    abstract protected byte[] getSplitPoint(final byte[] splitPoint);

    /**
     * Create the EntityGroupSplitPolicy configured for the given table. Each
     * 
     * @param htd
     * @param conf
     * @return
     * @throws java.io.IOException
     */
    public static EntityGroupSplitPolicy create(EntityGroup entityGroup, Configuration conf) throws IOException {

        Class<? extends EntityGroupSplitPolicy> clazz = getSplitPolicyClass(entityGroup.getTableDesc(), conf);
        EntityGroupSplitPolicy policy = ReflectionUtils.newInstance(clazz, conf);
        policy.configureForEntityGroup(entityGroup);
        return policy;
    }

    static Class<? extends EntityGroupSplitPolicy> getSplitPolicyClass(FTable ftd, Configuration conf)
            throws IOException {
        String className = conf.get(FConstants.WASP_ENTITYGROUP_SPLIT_POLICY_KEY,
                DEFAULT_SPLIT_POLICY_CLASS.getName());

        try {
            Class<? extends EntityGroupSplitPolicy> clazz = Class.forName(className)
                    .asSubclass(EntityGroupSplitPolicy.class);
            return clazz;
        } catch (Exception e) {
            throw new IOException("Unable to load configured entityGroup split policy '" + className
                    + "' for table '" + ftd.getTableName() + "'", e);
        }
    }
}