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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.wali;

import java.io.IOException;
import java.util.Collection;
import java.util.Set;

/**
 * 

* A WriteAheadRepository is used to persist state that is otherwise kept * in-memory. The Repository does not provide any query capability except to * allow the data to be recovered upon restart of the system. *

* *

* A WriteAheadRepository operates by writing every update to an Edit Log. On * restart, the data can be recovered by replaying all of the updates that are * found in the Edit Log. This can, however, eventually result in very large * Edit Logs, which can both take up massive amounts of disk space and take a * long time to recover. In order to prevent this, the Repository provides a * Checkpointing capability. This allows the current in-memory state of the * Repository to be flushed to disk and the Edit Log to be deleted, thereby * compacting the amount of space required to store the Repository. After a * Checkpoint is performed, modifications are again written to an Edit Log. At * this point, when the system is to be restored, it is restored by first * loading the Checkpointed version of the Repository and then replaying the * Edit Log. *

* *

* All implementations of WriteAheadRepository use one or more * partitions to manage their Edit Logs. An implementation may require exactly * one partition or may allow many partitions. *

* * @param the type of Record this repository is for */ public interface WriteAheadRepository { /** *

* Updates the repository with the specified Records. The Collection must * not contain multiple records with the same ID *

* * @param records the records to update * @param forceSync specifies whether or not the Repository forces the data * to be flushed to disk. If false, the data may be stored in Operating * System buffers, which improves performance but could cause loss of data * if power is lost or the Operating System crashes * @throws IOException if failure to update repo * @throws IllegalArgumentException if multiple records within the given * Collection have the same ID, as specified by {@link SerDe#getRecordIdentifier(Object)} * method * * @return the index of the Partition that performed the update */ int update(Collection records, boolean forceSync) throws IOException; /** *

* Recovers all records from the persisted state. This method must be called * before any updates are issued to the Repository. *

* * @return recovered records * @throws IOException if failure to read from repo * @throws IllegalStateException if any updates have been issued against * this Repository before this method is invoked */ Collection recoverRecords() throws IOException; /** *

* Recovers all External Swap locations that were persisted. If this method * is to be called, it must be called AFTER {@link #recoverRecords()} and * BEFORE {@link #update(Collection, boolean)}}. *

* * @return swap location * @throws IOException if failure reading swap locations */ Set getRecoveredSwapLocations() throws IOException; /** *

* Compacts the contents of the Repository so that rather than having a * Snapshot and an Edit Log indicating many Updates to the Snapshot, the * Snapshot is updated to contain the current state of the Repository, and * the edit log is purged. *

* * * @return the number of records that were written to the new snapshot * @throws java.io.IOException if failure during checkpoint */ int checkpoint() throws IOException; /** *

* Causes the repository to checkpoint and then close any open resources. *

* * @throws IOException if failure to shutdown cleanly */ void shutdown() throws IOException; }




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