/**
* 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.hadoop.hdfs.server.namenode;
import java.io.Closeable;
import java.io.IOException;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.hdfs.server.common.Storage;
import org.apache.hadoop.hdfs.server.common.Storage.FormatConfirmable;
import org.apache.hadoop.hdfs.server.common.StorageInfo;
import org.apache.hadoop.hdfs.server.protocol.NamespaceInfo;
/**
* A JournalManager is responsible for managing a single place of storing
* edit logs. It may correspond to multiple files, a backup node, etc.
* Even when the actual underlying storage is rolled, or failed and restored,
* each conceptual place of storage corresponds to exactly one instance of
* this class, which is created when the EditLog is first opened.
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public interface JournalManager extends Closeable, LogsPurgeable,
FormatConfirmable {
/**
* Format the underlying storage, removing any previously
* stored data.
*/
void format(NamespaceInfo ns) throws IOException;
/**
* Begin writing to a new segment of the log stream, which starts at
* the given transaction ID.
*/
EditLogOutputStream startLogSegment(long txId, int layoutVersion)
throws IOException;
/**
* Mark the log segment that spans from firstTxId to lastTxId
* as finalized and complete.
*/
void finalizeLogSegment(long firstTxId, long lastTxId) throws IOException;
/**
* Set the amount of memory that this stream should use to buffer edits
*/
void setOutputBufferCapacity(int size);
/**
* Recover segments which have not been finalized.
*/
void recoverUnfinalizedSegments() throws IOException;
/**
* Perform any steps that must succeed across all JournalManagers involved in
* an upgrade before proceeding onto the actual upgrade stage. If a call to
* any JM's doPreUpgrade method fails, then doUpgrade will not be called for
* any JM.
*/
void doPreUpgrade() throws IOException;
/**
* Perform the actual upgrade of the JM. After this is completed, the NN can
* begin to use the new upgraded metadata. This metadata may later be either
* finalized or rolled back to the previous state.
*
* @param storage info about the new upgraded versions.
*/
void doUpgrade(Storage storage) throws IOException;
/**
* Finalize the upgrade. JMs should purge any state that they had been keeping
* around during the upgrade process. After this is completed, rollback is no
* longer allowed.
*/
void doFinalize() throws IOException;
/**
* Return true if this JM can roll back to the previous storage state, false
* otherwise. The NN will refuse to run the rollback operation unless at least
* one JM or fsimage storage directory can roll back.
*
* @param storage the storage info for the current state
* @param prevStorage the storage info for the previous (unupgraded) state
* @param targetLayoutVersion the layout version we intend to roll back to
* @return true if this JM can roll back, false otherwise.
*/
boolean canRollBack(StorageInfo storage, StorageInfo prevStorage,
int targetLayoutVersion) throws IOException;
/**
* Perform the rollback to the previous FS state. JMs which do not need to
* roll back their state should just return without error.
*/
void doRollback() throws IOException;
/**
* @return the CTime of the journal manager.
*/
long getJournalCTime() throws IOException;
/**
* Discard the segments whose first txid is >= the given txid.
* @param startTxId The given txid should be right at the segment boundary,
* i.e., it should be the first txid of some segment, if segment corresponding
* to the txid exists.
*/
void discardSegments(long startTxId) throws IOException;
/**
* Close the journal manager, freeing any resources it may hold.
*/
@Override
void close() throws IOException;
/**
* Indicate that a journal is cannot be used to load a certain range of
* edits.
* This exception occurs in the case of a gap in the transactions, or a
* corrupt edit file.
*/
public static class CorruptionException extends IOException {
static final long serialVersionUID = -4687802717006172702L;
public CorruptionException(String reason) {
super(reason);
}
}
}