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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/**
* 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.cassandra.dht;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.nio.ByteBuffer;
import java.util.*;
import java.util.concurrent.ThreadLocalRandom;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.db.PreHashedDecoratedKey;
import org.apache.cassandra.db.marshal.AbstractType;
import org.apache.cassandra.db.marshal.PartitionerDefinedOrder;
import org.apache.cassandra.db.marshal.LongType;
import org.apache.cassandra.exceptions.ConfigurationException;
import org.apache.cassandra.utils.ByteBufferUtil;
import org.apache.cassandra.utils.MurmurHash;
import org.apache.cassandra.utils.ObjectSizes;
import com.google.common.primitives.Longs;
/**
* This class generates a BigIntegerToken using a Murmur3 hash.
*/
public class Murmur3Partitioner implements IPartitioner
{
public static final LongToken MINIMUM = new LongToken(Long.MIN_VALUE);
public static final long MAXIMUM = Long.MAX_VALUE;
private static final int HEAP_SIZE = (int) ObjectSizes.measureDeep(MINIMUM);
public static final Murmur3Partitioner instance = new Murmur3Partitioner();
public static final AbstractType partitionOrdering = new PartitionerDefinedOrder(instance);
public DecoratedKey decorateKey(ByteBuffer key)
{
long[] hash = getHash(key);
return new PreHashedDecoratedKey(getToken(key, hash), key, hash[0], hash[1]);
}
public Token midpoint(Token lToken, Token rToken)
{
// using BigInteger to avoid long overflow in intermediate operations
BigInteger l = BigInteger.valueOf(((LongToken) lToken).token),
r = BigInteger.valueOf(((LongToken) rToken).token),
midpoint;
if (l.compareTo(r) < 0)
{
BigInteger sum = l.add(r);
midpoint = sum.shiftRight(1);
}
else // wrapping case
{
BigInteger max = BigInteger.valueOf(MAXIMUM);
BigInteger min = BigInteger.valueOf(MINIMUM.token);
// length of range we're bisecting is (R - min) + (max - L)
// so we add that to L giving
// L + ((R - min) + (max - L) / 2) = (L + R + max - min) / 2
midpoint = (max.subtract(min).add(l).add(r)).shiftRight(1);
if (midpoint.compareTo(max) > 0)
midpoint = min.add(midpoint.subtract(max));
}
return new LongToken(midpoint.longValue());
}
public LongToken getMinimumToken()
{
return MINIMUM;
}
public static class LongToken extends Token
{
static final long serialVersionUID = -5833580143318243006L;
final long token;
public LongToken(long token)
{
this.token = token;
}
public String toString()
{
return Long.toString(token);
}
public boolean equals(Object obj)
{
if (this == obj)
return true;
if (obj == null || this.getClass() != obj.getClass())
return false;
return token == (((LongToken)obj).token);
}
public int hashCode()
{
return Longs.hashCode(token);
}
public int compareTo(Token o)
{
return Long.compare(token, ((LongToken) o).token);
}
@Override
public IPartitioner getPartitioner()
{
return instance;
}
@Override
public long getHeapSize()
{
return HEAP_SIZE;
}
@Override
public Object getTokenValue()
{
return token;
}
@Override
public double size(Token next)
{
LongToken n = (LongToken) next;
long v = n.token - token; // Overflow acceptable and desired.
double d = Math.scalb((double) v, -Long.SIZE); // Scale so that the full range is 1.
return d > 0.0 ? d : (d + 1.0); // Adjust for signed long, also making sure t.size(t) == 1.
}
@Override
public Token increaseSlightly()
{
return new LongToken(token + 1);
}
}
/**
* Generate the token of a key.
* Note that we need to ensure all generated token are strictly bigger than MINIMUM.
* In particular we don't want MINIMUM to correspond to any key because the range (MINIMUM, X] doesn't
* include MINIMUM but we use such range to select all data whose token is smaller than X.
*/
public LongToken getToken(ByteBuffer key)
{
return getToken(key, getHash(key));
}
private LongToken getToken(ByteBuffer key, long[] hash)
{
if (key.remaining() == 0)
return MINIMUM;
return new LongToken(normalize(hash[0]));
}
private long[] getHash(ByteBuffer key)
{
long[] hash = new long[2];
MurmurHash.hash3_x64_128(key, key.position(), key.remaining(), 0, hash);
return hash;
}
public LongToken getRandomToken()
{
return getRandomToken(ThreadLocalRandom.current());
}
public LongToken getRandomToken(Random r)
{
return new LongToken(normalize(r.nextLong()));
}
private long normalize(long v)
{
// We exclude the MINIMUM value; see getToken()
return v == Long.MIN_VALUE ? Long.MAX_VALUE : v;
}
public boolean preservesOrder()
{
return false;
}
public Map describeOwnership(List sortedTokens)
{
Map ownerships = new HashMap();
Iterator i = sortedTokens.iterator();
// 0-case
if (!i.hasNext())
throw new RuntimeException("No nodes present in the cluster. Has this node finished starting up?");
// 1-case
if (sortedTokens.size() == 1)
ownerships.put(i.next(), new Float(1.0));
// n-case
else
{
final BigInteger ri = BigInteger.valueOf(MAXIMUM).subtract(BigInteger.valueOf(MINIMUM.token + 1)); // (used for addition later)
final BigDecimal r = new BigDecimal(ri);
Token start = i.next();BigInteger ti = BigInteger.valueOf(((LongToken)start).token); // The first token and its value
Token t; BigInteger tim1 = ti; // The last token and its value (after loop)
while (i.hasNext())
{
t = i.next(); ti = BigInteger.valueOf(((LongToken) t).token); // The next token and its value
float age = new BigDecimal(ti.subtract(tim1).add(ri).mod(ri)).divide(r, 6, BigDecimal.ROUND_HALF_EVEN).floatValue(); // %age = ((T(i) - T(i-1) + R) % R) / R
ownerships.put(t, age); // save (T(i) -> %age)
tim1 = ti; // -> advance loop
}
// The start token's range extends backward to the last token, which is why both were saved above.
float x = new BigDecimal(BigInteger.valueOf(((LongToken)start).token).subtract(ti).add(ri).mod(ri)).divide(r, 6, BigDecimal.ROUND_HALF_EVEN).floatValue();
ownerships.put(start, x);
}
return ownerships;
}
public Token.TokenFactory getTokenFactory()
{
return tokenFactory;
}
private final Token.TokenFactory tokenFactory = new Token.TokenFactory()
{
public ByteBuffer toByteArray(Token token)
{
LongToken longToken = (LongToken) token;
return ByteBufferUtil.bytes(longToken.token);
}
public Token fromByteArray(ByteBuffer bytes)
{
return new LongToken(ByteBufferUtil.toLong(bytes));
}
public String toString(Token token)
{
return token.toString();
}
public void validate(String token) throws ConfigurationException
{
try
{
Long.valueOf(token);
}
catch (NumberFormatException e)
{
throw new ConfigurationException(e.getMessage());
}
}
public Token fromString(String string)
{
try
{
return new LongToken(Long.parseLong(string));
}
catch (NumberFormatException e)
{
throw new IllegalArgumentException(String.format("Invalid token for Murmur3Partitioner. Got %s but expected a long value (unsigned 8 bytes integer).", string));
}
}
};
public AbstractType getTokenValidator()
{
return LongType.instance;
}
public AbstractType partitionOrdering()
{
return partitionOrdering;
}
}