org.apache.hadoop.hdfs.server.blockmanagement.SequentialBlockIdGenerator 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.apache.hadoop.hdfs.server.blockmanagement;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.hdfs.protocol.Block;
import org.apache.hadoop.hdfs.server.namenode.INodeId;
import org.apache.hadoop.util.SequentialNumber;
/**
* Generate the next valid block ID by incrementing the maximum block
* ID allocated so far, starting at 2^30+1.
*
* Block IDs used to be allocated randomly in the past. Hence we may
* find some conflicts while stepping through the ID space sequentially.
* However given the sparsity of the ID space, conflicts should be rare
* and can be skipped over when detected.
*/
@InterfaceAudience.Private
public class SequentialBlockIdGenerator extends SequentialNumber {
/**
* The last reserved block ID.
*/
public static final long LAST_RESERVED_BLOCK_ID = 1024L * 1024 * 1024;
private final BlockManager blockManager;
SequentialBlockIdGenerator(BlockManager blockManagerRef) {
super(LAST_RESERVED_BLOCK_ID);
this.blockManager = blockManagerRef;
}
@Override // NumberGenerator
public long nextValue() {
Block b = new Block(super.nextValue());
// There may be an occasional conflict with randomly generated
// block IDs. Skip over the conflicts.
while(isValidBlock(b)) {
b.setBlockId(super.nextValue());
}
if (b.getBlockId() < 0) {
throw new IllegalStateException("All positive block IDs are used, " +
"wrapping to negative IDs, " +
"which might conflict with erasure coded block groups.");
}
return b.getBlockId();
}
/**
* Returns whether the given block is one pointed-to by a file.
*/
private boolean isValidBlock(Block b) {
BlockInfo bi = blockManager.getStoredBlock(b);
return bi != null && bi.getBlockCollectionId() !=
INodeId.INVALID_INODE_ID;
}
}