RandomBalanceStrategy.java

/*
 Copyright (c) 2007, 2012, Oracle and/or its affiliates. All rights reserved.
 

  The MySQL Connector/J is licensed under the terms of the GPLv2
  <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
  There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
  this software, see the FLOSS License Exception
  <http://www.mysql.com/about/legal/licensing/foss-exception.html>.

  This program 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; version 2
  of the License.

  This program 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 this
  program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
  Floor, Boston, MA 02110-1301  USA
 
 */
package com.mysql.jdbc;

import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;

public class RandomBalanceStrategy implements BalanceStrategy {

	public RandomBalanceStrategy() {
	}

	public void destroy() {
		// we don't have anything to clean up
	}

	public void init(Connection conn, Properties props) throws SQLException {
		// we don't have anything to initialize
	}

	public ConnectionImpl pickConnection(LoadBalancingConnectionProxy proxy,
			List<String> configuredHosts, Map<String, ConnectionImpl> liveConnections, long[] responseTimes,
			int numRetries) throws SQLException {
		int numHosts = configuredHosts.size();

		SQLException ex = null;

		List<String> whiteList = new ArrayList<String>(numHosts);
		whiteList.addAll(configuredHosts);
		
		Map<String, Long> blackList = proxy.getGlobalBlacklist();

		whiteList.removeAll(blackList.keySet());
		
		Map<String, Integer> whiteListMap = this.getArrayIndexMap(whiteList);
		

		for (int attempts = 0; attempts < numRetries;) {
			int random = (int) Math.floor((Math.random() * whiteList.size()));
			if(whiteList.size() == 0){
				throw SQLError.createSQLException("No hosts configured", null);
			}

			String hostPortSpec = whiteList.get(random);

			ConnectionImpl conn = liveConnections.get(hostPortSpec);

			if (conn == null) {
				try {
					conn = proxy.createConnectionForHost(hostPortSpec);
				} catch (SQLException sqlEx) {
					ex = sqlEx;

					if (proxy.shouldExceptionTriggerFailover(sqlEx)) {

						Integer whiteListIndex = whiteListMap.get(hostPortSpec);

						// exclude this host from being picked again
						if (whiteListIndex != null) {
							whiteList.remove(whiteListIndex.intValue());
							whiteListMap = this.getArrayIndexMap(whiteList);
						}
						proxy.addToGlobalBlacklist( hostPortSpec );

						if (whiteList.size() == 0) {
							attempts++;
							try {
								Thread.sleep(250);
							} catch (InterruptedException e) {
							}

							// start fresh
							whiteListMap = new HashMap<String, Integer>(numHosts);
							whiteList.addAll(configuredHosts);
							blackList = proxy.getGlobalBlacklist();

							whiteList.removeAll(blackList.keySet());
							whiteListMap = this.getArrayIndexMap(whiteList);
						}

						continue;
					}

					throw sqlEx;
				}
			}
			
			return conn;
		}

		if (ex != null) {
			throw ex;
		}

		return null; // we won't get here, compiler can't tell
	}
	
	private Map<String, Integer> getArrayIndexMap(List<String> l) {
		Map<String, Integer> m = new HashMap<String, Integer>(l.size());
		for (int i = 0; i < l.size(); i++) {
			m.put(l.get(i), Integer.valueOf(i));
		}
		return m;
		
	}

}