/* This file is part of VoltDB.
* Copyright (C) 2008-2010 VoltDB L.L.C.
*
* VoltDB is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* VoltDB is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with VoltDB. If not, see <http://www.gnu.org/licenses/>.
*/
package org.voltdb;
import java.io.UnsupportedEncodingException;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;
import org.voltdb.catalog.Catalog;
import org.voltdb.catalog.Cluster;
import org.voltdb.utils.LogKeys;
import org.voltdb.utils.VoltLoggerFactory;
import edu.brown.hstore.HStore;
/**
* Class that maps object values to partitions. It's rather simple
* really. It'll get more complicated if you give it time.
*/
public abstract class TheHashinator {
static int partitionCount;
private static final Logger hostLogger = Logger.getLogger("HOST", VoltLoggerFactory.instance());
/**
* Initialize TheHashinator
* @param catalog A pointer to the catalog data structure.
*/
public static void initialize(Catalog catalog) {
Cluster cluster = catalog.getClusters().get("cluster");
partitionCount = cluster.getNum_partitions();
}
/**
* Given a long value, pick a partition to store the data.
*
* @param value The value to hash.
* @param partitionCount The number of partitions to choose from.
* @return A value between 0 and partitionCount-1, hopefully pretty evenly
* distributed.
*/
static int hashinate(long value, int partitionCount) {
int index = (int)(value^(value>>>32));
return java.lang.Math.abs(index % partitionCount);
}
/**
* Given an Object value, pick a partition to store the data. Currently only String objects can be hashed.
*
* @param value The value to hash.
* @param partitionCount The number of partitions to choose from.
* @return A value between 0 and partitionCount-1, hopefully pretty evenly
* distributed.
*/
static int hashinate(Object value, int partitionCount) {
if (value instanceof String) {
String string = (String) value;
try {
byte bytes[] = string.getBytes("UTF-8");
int hashCode = 0;
int offset = 0;
for (int ii = 0; ii < bytes.length; ii++) {
hashCode = 31 * hashCode + bytes[offset++];
}
return java.lang.Math.abs(hashCode % partitionCount);
} catch (UnsupportedEncodingException e) {
hostLogger.l7dlog( Level.FATAL, LogKeys.host_TheHashinator_ExceptionHashingString.name(), new Object[] { string }, e);
HStore.crashDB();
}
}
hostLogger.l7dlog(Level.FATAL, LogKeys.host_TheHashinator_AttemptedToHashinateNonLongOrString.name(), new Object[] { value
.getClass().getName() }, null);
HStore.crashDB();
return -1;
}
/**
* Given an object, map it to a partition.
* @param obj The object to be mapped to a partition.
* @return The id of the partition desired.
*/
public static int hashToPartition(Object obj) {
return (hashToPartition(obj, TheHashinator.partitionCount));
}
/**
* Given an object and a number of partitions, map the object to a partition.
* @param obj The object to be mapped to a partition.
* @param partitionCount The number of partitions TheHashinator will use
* @return The id of the partition desired.
*/
public static int hashToPartition(Object obj, int partitionCount) {
int index = 0;
if (obj instanceof Long) {
long value = ((Long) obj).longValue();
index = hashinate(value, partitionCount);
} else if (obj instanceof String) {
index = hashinate(obj, partitionCount);
} else if (obj instanceof Integer) {
long value = (long)((Integer)obj).intValue();
index = hashinate(value, partitionCount);
} else if (obj instanceof Short) {
long value = (long)((Short)obj).shortValue();
index = hashinate(value, partitionCount);
} else if (obj instanceof Byte) {
long value = (long)((Byte)obj).byteValue();
index = hashinate(value, partitionCount);
}
return index;
}
}