/*
Copyright (c) 2010, 2015, 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.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.SQLException;
import java.util.List;
import java.util.Properties;
import java.util.concurrent.Executor;
/**
* A proxy for a dynamic com.mysql.jdbc.Connection implementation that provides failover features for list of hosts. Connection switching occurs on
* communications related exceptions and/or user defined settings, namely when one of the conditions set in 'secondsBeforeRetryMaster' or
* 'queriesBeforeRetryMaster' is met.
*/
public class FailoverConnectionProxy extends MultiHostConnectionProxy {
private static final String METHOD_SET_READ_ONLY = "setReadOnly";
private static final String METHOD_SET_AUTO_COMMIT = "setAutoCommit";
private static final String METHOD_COMMIT = "commit";
private static final String METHOD_ROLLBACK = "rollback";
private static final int NO_CONNECTION_INDEX = -1;
private static final int DEFAULT_PRIMARY_HOST_INDEX = 0;
private int secondsBeforeRetryPrimaryHost;
private long queriesBeforeRetryPrimaryHost;
private boolean failoverReadOnly;
private int retriesAllDown;
private int currentHostIndex = NO_CONNECTION_INDEX;
private int primaryHostIndex = DEFAULT_PRIMARY_HOST_INDEX;
private Boolean explicitlyReadOnly = null;
private boolean explicitlyAutoCommit = true;
private boolean enableFallBackToPrimaryHost = true;
private long primaryHostFailTimeMillis = 0;
private long queriesIssuedSinceFailover = 0;
/**
* Proxy class to intercept and deal with errors that may occur in any object bound to the current connection.
* Additionally intercepts query executions and triggers an execution count on the outer class.
*/
class FailoverJdbcInterfaceProxy extends JdbcInterfaceProxy {
FailoverJdbcInterfaceProxy(Object toInvokeOn) {
super(toInvokeOn);
}
@SuppressWarnings("synthetic-access")
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
boolean isExecute = methodName.startsWith("execute");
if (FailoverConnectionProxy.this.connectedToSecondaryHost() && isExecute) {
FailoverConnectionProxy.this.incrementQueriesIssuedSinceFailover();
}
Object result = super.invoke(proxy, method, args);
if (FailoverConnectionProxy.this.explicitlyAutoCommit && isExecute && readyToFallBackToPrimaryHost()) {
// Fall back to primary host at transaction boundary
fallBackToPrimaryIfAvailable();
}
return result;
}
}
/**
* Instantiates a new FailoverConnectionProxy for the given list of host and connection properties.
*
* @param hosts
* The lists of hosts available to switch on.
* @param props
* The properties to be used in new internal connections.
*/
FailoverConnectionProxy(List<String> hosts, Properties props) throws SQLException {
super(hosts, props);
ConnectionPropertiesImpl connProps = new ConnectionPropertiesImpl();
connProps.initializeProperties(props);
this.secondsBeforeRetryPrimaryHost = connProps.getSecondsBeforeRetryMaster();
this.queriesBeforeRetryPrimaryHost = connProps.getQueriesBeforeRetryMaster();
this.failoverReadOnly = connProps.getFailOverReadOnly();
this.retriesAllDown = connProps.getRetriesAllDown();
this.enableFallBackToPrimaryHost = this.secondsBeforeRetryPrimaryHost > 0 || this.queriesBeforeRetryPrimaryHost > 0;
pickNewConnection();
this.explicitlyAutoCommit = this.currentConnection.getAutoCommit();
}
/*
* Gets locally bound instances of FailoverJdbcInterfaceProxy.
*
* @see com.mysql.jdbc.MultiHostConnectionProxy#getNewJdbcInterfaceProxy(java.lang.Object)
*/
@Override
JdbcInterfaceProxy getNewJdbcInterfaceProxy(Object toProxy) {
return new FailoverJdbcInterfaceProxy(toProxy);
}
/*
* Local implementation for the connection switch exception checker.
*
* @see com.mysql.jdbc.MultiHostConnectionProxy#shouldExceptionTriggerConnectionSwitch(java.lang.Throwable)
*/
@Override
boolean shouldExceptionTriggerConnectionSwitch(Throwable t) {
if (!(t instanceof SQLException)) {
return false;
}
String sqlState = ((SQLException) t).getSQLState();
if (sqlState != null) {
if (sqlState.startsWith("08")) {
// connection error
return true;
}
}
// Always handle CommunicationsException
if (t instanceof CommunicationsException) {
return true;
}
return false;
}
/*
* Local implementation for the new connection picker.
*
* @see com.mysql.jdbc.MultiHostConnectionProxy#pickNewConnection()
*/
@Override
synchronized void pickNewConnection() throws SQLException {
if (this.isClosed && this.closedExplicitly) {
return;
}
if (!isConnected() || readyToFallBackToPrimaryHost()) {
try {
connectTo(this.primaryHostIndex);
} catch (SQLException e) {
resetAutoFallBackCounters();
failOver(this.primaryHostIndex);
}
} else {
failOver();
}
}
/**
* Creates a new connection instance for host pointed out by the given host index.
*
* @param hostIndex
* The host index in the global hosts list.
* @return
* The new connection instance.
*/
synchronized ConnectionImpl createConnectionForHostIndex(int hostIndex) throws SQLException {
return createConnectionForHost(this.hostList.get(hostIndex));
}
/**
* Connects this dynamic failover connection proxy to the host pointed out by the given host index.
*
* @param hostIndex
* The host index in the global hosts list.
*/
private synchronized void connectTo(int hostIndex) throws SQLException {
try {
switchCurrentConnectionTo(hostIndex, createConnectionForHostIndex(hostIndex));
} catch (SQLException e) {
if (this.currentConnection != null) {
StringBuilder msg = new StringBuilder("Connection to ").append(isPrimaryHostIndex(hostIndex) ? "primary" : "secondary").append(" host '")
.append(this.hostList.get(hostIndex)).append("' failed");
this.currentConnection.getLog().logWarn(msg.toString(), e);
}
throw e;
}
}
/**
* Replaces the previous underlying connection by the connection given. State from previous connection, if any, is synchronized with the new one.
*
* @param hostIndex
* The host index in the global hosts list that matches the given connection.
* @param connection
* The connection instance to switch to.
*/
private synchronized void switchCurrentConnectionTo(int hostIndex, MySQLConnection connection) throws SQLException {
invalidateCurrentConnection();
boolean readOnly;
if (isPrimaryHostIndex(hostIndex)) {
readOnly = this.explicitlyReadOnly == null ? false : this.explicitlyReadOnly;
} else if (this.failoverReadOnly) {
readOnly = true;
} else if (this.explicitlyReadOnly != null) {
readOnly = this.explicitlyReadOnly;
} else if (this.currentConnection != null) {
readOnly = this.currentConnection.isReadOnly();
} else {
readOnly = false;
}
syncSessionState(this.currentConnection, connection, readOnly);
this.currentConnection = connection;
this.currentHostIndex = hostIndex;
}
/**
* Initiates a default failover procedure starting at the current connection host index.
*/
private synchronized void failOver() throws SQLException {
failOver(this.currentHostIndex);
}
/**
* Initiates a default failover procedure starting at the given host index.
* This process tries to connect, sequentially, to the next host in the list. The primary host may or may not be excluded from the connection attempts.
*
* @param failedHostIdx
* The host index where to start from. First connection attempt will be the next one.
*/
private synchronized void failOver(int failedHostIdx) throws SQLException {
int prevHostIndex = this.currentHostIndex;
int nextHostIndex = nextHost(failedHostIdx, false);
int firstHostIndexTried = nextHostIndex;
SQLException lastExceptionCaught = null;
int attempts = 0;
boolean gotConnection = false;
boolean firstConnOrPassedByPrimaryHost = prevHostIndex == NO_CONNECTION_INDEX || isPrimaryHostIndex(prevHostIndex);
do {
try {
firstConnOrPassedByPrimaryHost = firstConnOrPassedByPrimaryHost || isPrimaryHostIndex(nextHostIndex);
connectTo(nextHostIndex);
if (firstConnOrPassedByPrimaryHost && connectedToSecondaryHost()) {
resetAutoFallBackCounters();
}
gotConnection = true;
} catch (SQLException e) {
lastExceptionCaught = e;
if (shouldExceptionTriggerConnectionSwitch(e)) {
int newNextHostIndex = nextHost(nextHostIndex, attempts > 0);
if (newNextHostIndex == firstHostIndexTried && newNextHostIndex == (newNextHostIndex = nextHost(nextHostIndex, true))) { // Full turn
attempts++;
try {
Thread.sleep(250);
} catch (InterruptedException ie) {
}
}
nextHostIndex = newNextHostIndex;
} else {
throw e;
}
}
} while (attempts < this.retriesAllDown && !gotConnection);
if (!gotConnection) {
throw lastExceptionCaught;
}
}
/**
* Falls back to primary host or keep current connection if primary not available.
*/
synchronized void fallBackToPrimaryIfAvailable() {
MySQLConnection connection = null;
try {
connection = createConnectionForHostIndex(this.primaryHostIndex);
switchCurrentConnectionTo(this.primaryHostIndex, connection);
} catch (SQLException e1) {
if (connection != null) {
try {
connection.close();
} catch (SQLException e2) {
}
}
// Keep current connection and reset counters
resetAutoFallBackCounters();
}
}
/**
* Gets the next host on the hosts list. Uses a round-robin algorithm to find the next element, but it may skip the index for the primary host.
* General rules to include the primary host are:
* - not currently connected to any host.
* - primary host is vouched (usually because connection to all secondary hosts has failed).
* - conditions to fall back to primary host are met (or they are disabled).
*
* @param currHostIdx
* Current host index.
* @param vouchForPrimaryHost
* Allows to return the primary host index even if the usual required conditions aren't met.
*/
private int nextHost(int currHostIdx, boolean vouchForPrimaryHost) {
int nextHostIdx = (currHostIdx + 1) % this.hostList.size();
if (isPrimaryHostIndex(nextHostIdx) && isConnected() && !vouchForPrimaryHost && this.enableFallBackToPrimaryHost && !readyToFallBackToPrimaryHost()) {
// Skip primary host, assume this.hostList.size() >= 2
nextHostIdx = nextHost(nextHostIdx, vouchForPrimaryHost);
}
return nextHostIdx;
}
/**
* Increments counter for query executions.
*/
synchronized void incrementQueriesIssuedSinceFailover() {
this.queriesIssuedSinceFailover++;
}
/**
* Checks if at least one of the required conditions to fall back to primary host is met, which is determined by the properties 'queriesBeforeRetryMaster'
* and 'secondsBeforeRetryMaster'.
*/
synchronized boolean readyToFallBackToPrimaryHost() {
return this.enableFallBackToPrimaryHost && connectedToSecondaryHost() && (secondsBeforeRetryPrimaryHostIsMet() || queriesBeforeRetryPrimaryHostIsMet());
}
/**
* Checks if there is a underlying connection for this proxy.
*/
synchronized boolean isConnected() {
return this.currentHostIndex != NO_CONNECTION_INDEX;
}
/**
* Checks if the given host index points to the primary host.
*
* @param hostIndex
* The host index in the global hosts list.
*/
synchronized boolean isPrimaryHostIndex(int hostIndex) {
return hostIndex == this.primaryHostIndex;
}
/**
* Checks if this proxy is using the primary host in the underlying connection.
*/
synchronized boolean connectedToPrimaryHost() {
return isPrimaryHostIndex(this.currentHostIndex);
}
/**
* Checks if this proxy is using a secondary host in the underlying connection.
*/
synchronized boolean connectedToSecondaryHost() {
return this.currentHostIndex >= 0 && !isPrimaryHostIndex(this.currentHostIndex);
}
/**
* Checks the condition set by the property 'secondsBeforeRetryMaster'.
*/
private synchronized boolean secondsBeforeRetryPrimaryHostIsMet() {
return this.secondsBeforeRetryPrimaryHost > 0 && Util.secondsSinceMillis(this.primaryHostFailTimeMillis) >= this.secondsBeforeRetryPrimaryHost;
}
/**
* Checks the condition set by the property 'queriesBeforeRetryMaster'.
*/
private synchronized boolean queriesBeforeRetryPrimaryHostIsMet() {
return this.queriesBeforeRetryPrimaryHost > 0 && this.queriesIssuedSinceFailover >= this.queriesBeforeRetryPrimaryHost;
}
/**
* Resets auto-fall back counters.
*/
private synchronized void resetAutoFallBackCounters() {
this.primaryHostFailTimeMillis = System.currentTimeMillis();
this.queriesIssuedSinceFailover = 0;
}
/**
* Closes current connection.
*/
@Override
synchronized void doClose() throws SQLException {
this.currentConnection.close();
}
/**
* Aborts current connection.
*/
@Override
synchronized void doAbortInternal() throws SQLException {
this.currentConnection.abortInternal();
}
/**
* Aborts current connection using the given executor.
*/
@Override
synchronized void doAbort(Executor executor) throws SQLException {
this.currentConnection.abort(executor);
}
/*
* Local method invocation handling for this proxy.
* This is the continuation of MultiHostConnectionProxy#invoke(Object, Method, Object[]).
*/
@Override
public synchronized Object invokeMore(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
if (METHOD_SET_READ_ONLY.equals(methodName)) {
this.explicitlyReadOnly = (Boolean) args[0];
if (this.failoverReadOnly && connectedToSecondaryHost()) {
return null;
}
}
if (this.isClosed) {
if (this.autoReconnect && !this.closedExplicitly) {
this.currentHostIndex = NO_CONNECTION_INDEX; // Act as if this is the first connection but let it sync with the previous one.
pickNewConnection();
this.isClosed = false;
this.closedReason = null;
} else {
String reason = "No operations allowed after connection closed.";
if (this.closedReason != null) {
reason += (" " + this.closedReason);
}
throw SQLError.createSQLException(reason, SQLError.SQL_STATE_CONNECTION_NOT_OPEN, null /* no access to a interceptor here... */);
}
}
Object result = null;
try {
result = method.invoke(this.thisAsConnection, args);
result = proxyIfIsJdbcInterface(result);
} catch (InvocationTargetException e) {
dealWithInvocationException(e);
}
if (METHOD_SET_AUTO_COMMIT.equals(methodName)) {
this.explicitlyAutoCommit = (Boolean) args[0];
}
if ((this.explicitlyAutoCommit || METHOD_COMMIT.equals(methodName) || METHOD_ROLLBACK.equals(methodName)) && readyToFallBackToPrimaryHost()) {
// Fall back to primary host at transaction boundary
fallBackToPrimaryIfAvailable();
}
return result;
}
}