spark WriteAheadLog 源码
spark WriteAheadLog 代码
文件路径：/streaming/src/main/java/org/apache/spark/streaming/util/WriteAheadLog.java
/*
* 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.spark.streaming.util;
import java.nio.ByteBuffer;
import java.util.Iterator;
/**
* :: DeveloperApi ::
*
* This abstract class represents a write ahead log (aka journal) that is used by Spark Streaming
* to save the received data (by receivers) and associated metadata to a reliable storage, so that
* they can be recovered after driver failures. See the Spark documentation for more information
* on how to plug in your own custom implementation of a write ahead log.
*/
@org.apache.spark.annotation.DeveloperApi
public abstract class WriteAheadLog {
/**
* Write the record to the log and return a record handle, which contains all the information
* necessary to read back the written record. The time is used to the index the record,
* such that it can be cleaned later. Note that implementations of this abstract class must
* ensure that the written data is durable and readable (using the record handle) by the
* time this function returns.
*/
public abstract WriteAheadLogRecordHandle write(ByteBuffer record, long time);
/**
* Read a written record based on the given record handle.
*/
public abstract ByteBuffer read(WriteAheadLogRecordHandle handle);
/**
* Read and return an iterator of all the records that have been written but not yet cleaned up.
*/
public abstract Iterator<ByteBuffer> readAll();
/**
* Clean all the records that are older than the threshold time. It can wait for
* the completion of the deletion.
*/
public abstract void clean(long threshTime, boolean waitForCompletion);
/**
* Close this log and release any resources. It must be idempotent.
*/
public abstract void close();
}
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