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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.accumulo.tserver.compaction;
import java.io.IOException;
import java.util.Map;
/**
* The interface for customizing major compactions.
*
* The tablet server has one thread to ask many tablets if they should compact. When the strategy
* returns true, then tablet is added to the queue of tablets waiting for a compaction thread. Once
* a thread is available, the {@link #gatherInformation(MajorCompactionRequest)} method is called
* outside the tablets' lock. This gives the strategy the ability to read information that maybe
* expensive to fetch. Once the gatherInformation returns, the tablet lock is grabbed and the
* compactionPlan computed. This should *not* do expensive operations, especially not I/O. Note that
* the number of files may change between calls to
* {@link #gatherInformation(MajorCompactionRequest)} and
* {@link #getCompactionPlan(MajorCompactionRequest)}.
*
* Note: the strategy object used for the {@link #shouldCompact(MajorCompactionRequest)} call
* is going to be different from the one used in the compaction thread.
*/
public abstract class CompactionStrategy {
/**
* The settings for the compaction strategy pulled from zookeeper. The
* table.compacations.major.strategy.opts part of the setting will be removed.
*/
public void init(Map options) {}
/**
* Determine if this tablet is eligible for a major compaction. It's ok if it later determines
* (through {@link #gatherInformation(MajorCompactionRequest)} and
* {@link #getCompactionPlan(MajorCompactionRequest)}) that it does not need to. Any state stored
* during shouldCompact will no longer exist when
* {@link #gatherInformation(MajorCompactionRequest)} and
* {@link #getCompactionPlan(MajorCompactionRequest)} are called.
*
*
* Called while holding the tablet lock, so it should not be doing any blocking.
*
*
* Since no blocking should be done in this method, then its unexpected that this method will
* throw IOException. However since its in the API, it can not be easily removed.
*/
public abstract boolean shouldCompact(MajorCompactionRequest request) throws IOException;
/**
* Called prior to obtaining the tablet lock, useful for examining metadata or indexes. State
* collected during this method will be available during the call the
* {@link #getCompactionPlan(MajorCompactionRequest)}.
*
* @param request
* basic details about the tablet
*/
public void gatherInformation(MajorCompactionRequest request) throws IOException {}
/**
* Get the plan for compacting a tablets files. Called while holding the tablet lock, so it should
* not be doing any blocking.
*
*
* Since no blocking should be done in this method, then its unexpected that this method will
* throw IOException. However since its in the API, it can not be easily removed.
*
* @param request
* basic details about the tablet
* @return the plan for a major compaction, or null to cancel the compaction.
*/
public abstract CompactionPlan getCompactionPlan(MajorCompactionRequest request)
throws IOException;
}