/**
* 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.nio.charset.CharacterCodingException;
import java.util.*;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.utils.ByteBufferUtil;
import org.apache.cassandra.utils.FBUtilities;
import org.apache.cassandra.utils.GuidGenerator;
import org.apache.cassandra.utils.Pair;
/**
* This class generates a BigIntegerToken using MD5 hash.
*/
public class RandomPartitioner implements IPartitioner<BigIntegerToken>
{
public static final BigInteger ZERO = new BigInteger("0");
public static final BigIntegerToken MINIMUM = new BigIntegerToken("-1");
private static final byte DELIMITER_BYTE = ":".getBytes()[0];
public DecoratedKey<BigIntegerToken> decorateKey(ByteBuffer key)
{
return new DecoratedKey<BigIntegerToken>(getToken(key), key);
}
public DecoratedKey<BigIntegerToken> convertFromDiskFormat(ByteBuffer fromdisk)
{
// find the delimiter position
int splitPoint = -1;
for (int i = fromdisk.position(); i < fromdisk.limit(); i++)
{
if (fromdisk.get(i) == DELIMITER_BYTE)
{
splitPoint = i;
break;
}
}
assert splitPoint != -1;
// and decode the token and key
String token = null;
try
{
token = ByteBufferUtil.string(fromdisk, fromdisk.position(), splitPoint - fromdisk.position());
}
catch (CharacterCodingException e)
{
throw new RuntimeException(e);
}
ByteBuffer key = fromdisk.duplicate();
key.position(splitPoint + 1);
return new DecoratedKey<BigIntegerToken>(new BigIntegerToken(token), key);
}
public Token midpoint(Token ltoken, Token rtoken)
{
// the symbolic MINIMUM token should act as ZERO: the empty bit array
BigInteger left = ltoken.equals(MINIMUM) ? ZERO : ((BigIntegerToken)ltoken).token;
BigInteger right = rtoken.equals(MINIMUM) ? ZERO : ((BigIntegerToken)rtoken).token;
Pair<BigInteger,Boolean> midpair = FBUtilities.midpoint(left, right, 127);
// discard the remainder
return new BigIntegerToken(midpair.left);
}
public BigIntegerToken getMinimumToken()
{
return MINIMUM;
}
public BigIntegerToken getRandomToken()
{
BigInteger token = FBUtilities.hashToBigInteger(GuidGenerator.guidAsBytes());
if ( token.signum() == -1 )
token = token.multiply(BigInteger.valueOf(-1L));
return new BigIntegerToken(token);
}
private final Token.TokenFactory<BigInteger> tokenFactory = new Token.TokenFactory<BigInteger>() {
public ByteBuffer toByteArray(Token<BigInteger> bigIntegerToken)
{
return ByteBuffer.wrap(bigIntegerToken.token.toByteArray());
}
public Token<BigInteger> fromByteArray(ByteBuffer bytes)
{
return new BigIntegerToken(new BigInteger(ByteBufferUtil.getArray(bytes)));
}
public String toString(Token<BigInteger> bigIntegerToken)
{
return bigIntegerToken.token.toString();
}
public Token<BigInteger> fromString(String string)
{
return new BigIntegerToken(new BigInteger(string));
}
};
public Token.TokenFactory<BigInteger> getTokenFactory()
{
return tokenFactory;
}
public boolean preservesOrder()
{
return false;
}
public BigIntegerToken getToken(ByteBuffer key)
{
if (key.remaining() == 0)
return MINIMUM;
return new BigIntegerToken(FBUtilities.hashToBigInteger(key));
}
public Map<Token, Float> describeOwnership(List<Token> sortedTokens)
{
Map<Token, Float> ownerships = new HashMap<Token, Float>();
Iterator i = sortedTokens.iterator();
// 0-case
if (!i.hasNext()) { throw new RuntimeException("No nodes present in the cluster. How did you call this?"); }
// 1-case
if (sortedTokens.size() == 1) {
ownerships.put((Token)i.next(), new Float(1.0));
}
// n-case
else {
// NOTE: All divisions must take place in BigDecimals, and all modulo operators must take place in BigIntegers.
final BigInteger ri = new BigInteger("2").pow(127); // (used for addition later)
final BigDecimal r = new BigDecimal(ri); // The entire range, 2**127
Token start = (Token)i.next(); BigInteger ti = ((BigIntegerToken)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 = (Token)i.next(); ti = ((BigIntegerToken)t).token; // The next token and its value
float x = new BigDecimal(ti.subtract(tim1).add(ri).mod(ri)).divide(r).floatValue(); // %age = ((T(i) - T(i-1) + R) % R) / R
ownerships.put(t, x); // 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(((BigIntegerToken)start).token.subtract(ti).add(ri).mod(ri)).divide(r).floatValue();
ownerships.put(start, x);
}
return ownerships;
}
}