org.wali.WriteAheadRepository Maven / Gradle / Ivy
/*
* 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;
}