com.mysql.jdbc.SequentialBalanceStrategy Maven / Gradle / Ivy

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MySQL JDBC Type 4 driver
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/*
  Copyright (c) 2007, 2019, Oracle and/or its affiliates. All rights reserved.

  The MySQL Connector/J is licensed under the terms of the GPLv2
  , 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 FOSS License Exception
  .

  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.List;
import java.util.Map;
import java.util.Properties;

/**
 * A balancing strategy that starts at a random point, and then advances in the list (wrapping around) for each new pickConnection() call.
 * 
 * The initial point selection, and subsequent point selections are blacklist-aware.
 */
public class SequentialBalanceStrategy implements BalanceStrategy {
    private int currentHostIndex = -1;

    public SequentialBalanceStrategy() {
    }

    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(LoadBalancedConnectionProxy proxy, List configuredHosts, Map liveConnections,
            long[] responseTimes, int numRetries) throws SQLException {
        int numHosts = configuredHosts.size();

        SQLException ex = null;

        Map blackList = proxy.getGlobalBlacklist();

        for (int attempts = 0; attempts < numRetries; attempts++) {
            if (numHosts == 1) {
                this.currentHostIndex = 0; // pathological case
            } else if (this.currentHostIndex == -1) {
                int random = (int) Math.floor((Math.random() * numHosts));

                for (int i = random; i < numHosts; i++) {
                    if (!blackList.containsKey(configuredHosts.get(i))) {
                        this.currentHostIndex = i;
                        break;
                    }
                }

                if (this.currentHostIndex == -1) {
                    for (int i = 0; i < random; i++) {
                        if (!blackList.containsKey(configuredHosts.get(i))) {
                            this.currentHostIndex = i;
                            break;
                        }
                    }
                }

                if (this.currentHostIndex == -1) {
                    blackList = proxy.getGlobalBlacklist(); // it may have changed
                    // and the proxy returns a copy

                    try {
                        Thread.sleep(250);
                    } catch (InterruptedException e) {
                    }

                    continue; // retry
                }
            } else {

                int i = this.currentHostIndex + 1;
                boolean foundGoodHost = false;

                for (; i < numHosts; i++) {
                    if (!blackList.containsKey(configuredHosts.get(i))) {
                        this.currentHostIndex = i;
                        foundGoodHost = true;
                        break;
                    }
                }

                if (!foundGoodHost) {
                    for (i = 0; i < this.currentHostIndex; i++) {
                        if (!blackList.containsKey(configuredHosts.get(i))) {
                            this.currentHostIndex = i;
                            foundGoodHost = true;
                            break;
                        }
                    }
                }

                if (!foundGoodHost) {
                    blackList = proxy.getGlobalBlacklist(); // it may have changed
                    // and the proxy returns a copy

                    try {
                        Thread.sleep(250);
                    } catch (InterruptedException e) {
                    }

                    continue; // retry
                }
            }

            String hostPortSpec = configuredHosts.get(this.currentHostIndex);

            ConnectionImpl conn = liveConnections.get(hostPortSpec);

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

                    if (proxy.shouldExceptionTriggerConnectionSwitch(sqlEx)) {

                        proxy.addToGlobalBlacklist(hostPortSpec);

                        try {
                            Thread.sleep(250);
                        } catch (InterruptedException e) {
                        }

                        continue;
                    }
                    throw sqlEx;
                }
            }

            return conn;
        }

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

        return null; // we won't get here, compiler can't tell
    }

}