MyCat源码分析系列之——SQL下发

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SQL下发

SQL下发指的是MyCat将解析并改造完成的SQL语句依次发送至相应的MySQL节点(datanode)的过程,该执行过程由NonBlockingSession.execute()触发:

public void execute(RouteResultset rrs, int type) {
// clear prev execute resources
clearHandlesResources();
if (LOGGER.isDebugEnabled()) {
StringBuilder s = new StringBuilder();
LOGGER.debug(s.append(source).append(rrs).toString() + " rrs ");
} // 检查路由结果是否为空
RouteResultsetNode[] nodes = rrs.getNodes();
if (nodes == null || nodes.length == 0 || nodes[0].getName() == null
|| nodes[0].getName().equals("")) {
source.writeErrMessage(ErrorCode.ER_NO_DB_ERROR,
"No dataNode found ,please check tables defined in schema:"
+ source.getSchema());
return;
}
if (nodes.length == 1) {
singleNodeHandler = new SingleNodeHandler(rrs, this);
try {
singleNodeHandler.execute();
} catch (Exception e) {
LOGGER.warn(new StringBuilder().append(source).append(rrs), e);
source.writeErrMessage(ErrorCode.ERR_HANDLE_DATA, e.toString());
}
} else {
boolean autocommit = source.isAutocommit();
SystemConfig sysConfig = MycatServer.getInstance().getConfig()
.getSystem();
int mutiNodeLimitType = sysConfig.getMutiNodeLimitType();
multiNodeHandler = new MultiNodeQueryHandler(type, rrs, autocommit,
this); try {
multiNodeHandler.execute();
} catch (Exception e) {
LOGGER.warn(new StringBuilder().append(source).append(rrs), e);
source.writeErrMessage(ErrorCode.ERR_HANDLE_DATA, e.toString());
}
}
}

从代码中可以看到,首先对于路由节点信息RouteResultsetNode[]进行了判断,如果不存在任何需要派发的节点则直接返回;如果是单节点操作,则创建SingleNodeHandler实例,并调用其execute();如果是多节点操作,则创建MultiNodeQueryHandler实例,并调用其execute()

下面先来看单节点操作的SQL下发过程,以下是SingleNodeHandler的execute()方法:

public void execute() throws Exception {
startTime=System.currentTimeMillis();
ServerConnection sc = session.getSource();
this.isRunning = true;
this.packetId = 0;
final BackendConnection conn = session.getTarget(node);
if (session.tryExistsCon(conn, node)) {
_execute(conn);
} else {
// create new connection MycatConfig conf = MycatServer.getInstance().getConfig();
PhysicalDBNode dn = conf.getDataNodes().get(node.getName());
dn.getConnection(dn.getDatabase(), sc.isAutocommit(), node, this,
node);
}
}

如果session已经有该datanode关联的后端连接(session.tryExistsCon(conn, node)返回true),则调用_execute()方法下发SQL指令;反之,则调用dn.getConnection()方法从连接池中获取一个可用连接或新建一个连接,并且由于第个参数将this作为ResponseHandler对象传入,获取到连接后会在PhysicalDatasource.takeCon()中调用handler.connectionAcquired(conn)完成回调,即SingleNodeHandler.connectionAcquired()

public void connectionAcquired(final BackendConnection conn) {
session.bindConnection(node, conn);
_execute(conn);
}

该方法先将获取到的后端连接关联到本session中,随后同样调用_execute()方法下发SQL指令。_execute()方法的实现如下:

private void _execute(BackendConnection conn) {
if (session.closed()) {
endRunning();
session.clearResources(true);
return;
}
conn.setResponseHandler(this);
try {
conn.execute(node, session.getSource(), session.getSource()
.isAutocommit());
} catch (Exception e1) {
executeException(conn, e1);
return;
}
}

首先,很重要的是通过conn.setResponseHandler(this)将SingleNodeHandler与当前后端连接(MySQLConnection)以及连接中包含的MySQLConnectionHandler实例关联起来,这样做的目的是当结果返回的时候可以回调SingleNodeHandler相应的方法处理。随后调用MySQLConnection.execute()

public void execute(RouteResultsetNode rrn, ServerConnection sc,
boolean autocommit) throws UnsupportedEncodingException {
if (!modifiedSQLExecuted && rrn.isModifySQL()) {
modifiedSQLExecuted = true;
}
String xaTXID = sc.getSession2().getXaTXID();
synAndDoExecute(xaTXID, rrn, sc.getCharsetIndex(), sc.getTxIsolation(),
autocommit);
} private void synAndDoExecute(String xaTxID, RouteResultsetNode rrn,
int clientCharSetIndex, int clientTxIsoLation,
boolean clientAutoCommit) {
String xaCmd = null; boolean conAutoComit = this.autocommit;
String conSchema = this.schema;
// never executed modify sql,so auto commit
boolean expectAutocommit = !modifiedSQLExecuted || isFromSlaveDB()
|| clientAutoCommit;
if (expectAutocommit == false && xaTxID != null && xaStatus == 0) {
clientTxIsoLation = Isolations.SERIALIZABLE;
xaCmd = "XA START " + xaTxID + ';'; }
int schemaSyn = conSchema.equals(oldSchema) ? 0 : 1;
int charsetSyn = (this.charsetIndex == clientCharSetIndex) ? 0 : 1;
int txIsoLationSyn = (txIsolation == clientTxIsoLation) ? 0 : 1;
int autoCommitSyn = (conAutoComit == expectAutocommit) ? 0 : 1;
int synCount = schemaSyn + charsetSyn + txIsoLationSyn + autoCommitSyn;
if (synCount == 0) {
// not need syn connection
sendQueryCmd(rrn.getStatement());
return;
}
CommandPacket schemaCmd = null;
StringBuilder sb = new StringBuilder();
if (schemaSyn == 1) {
schemaCmd = getChangeSchemaCommand(conSchema);
// getChangeSchemaCommand(sb, conSchema);
} if (charsetSyn == 1) {
getCharsetCommand(sb, clientCharSetIndex);
}
if (txIsoLationSyn == 1) {
getTxIsolationCommand(sb, clientTxIsoLation);
}
if (autoCommitSyn == 1) {
getAutocommitCommand(sb, expectAutocommit);
}
if (xaCmd != null) {
sb.append(xaCmd);
}
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("con need syn ,total syn cmd " + synCount
+ " commands " + sb.toString() + "schema change:"
+ (schemaCmd != null) + " con:" + this);
}
metaDataSyned = false;
statusSync = new StatusSync(xaCmd != null, conSchema,
clientCharSetIndex, clientTxIsoLation, expectAutocommit,
synCount);
// syn schema
if (schemaCmd != null) {
schemaCmd.write(this);
}
// and our query sql to multi command at last
sb.append(rrn.getStatement());
// syn and execute others
this.sendQueryCmd(sb.toString());
// waiting syn result...
}

其中又会调用synAndDoExecute()方法,顾名思义是同步并执行,同步的目的在于之前获取到的后端连接可能在自动提交模式、数据库名、事务隔离级别和字符集上与当前要求可能不同,因此在真正执行SQL语句之前需要检查并同步相应如上设置。

如果synCount==0,则说明不需要同步,直接调用sendQuery()发送指令即可;反之,将相应的设置语句依次append到sb中(数据库切换是个例外,直接发送了COM_INIT_DB包进行设置),并创建一个StatusSync对象,最后添加待执行的SQL语句,随后调用sendQuery()发送指令。到这里,大家可能会有疑问,在此将需更改的相关设置(数据库名、字符集等)与SQL语句一起发送(并不等待其设置成功与否),万一之前的更改失败怎么办?MyCat对此就是依靠之前创建的StatusSync对象来处理的,在结果合并的流程介绍中会具体解释。

到此为止,SingleNodeHandler的SQL语句下发过程就算是结束了,当然底层真正的下发是由负责处理一个连接读写事件的NIOSocketWR对象来执行的。

接下来,看多节点操作SQL语句下发过程,与单节点极其类似,以下是MultiNodeQueryHandler的execute()方法:

public void execute() throws Exception {
final ReentrantLock lock = this.lock;
lock.lock();
try {
this.reset(rrs.getNodes().length);
this.fieldsReturned = false;
this.affectedRows = 0L;
this.insertId = 0L;
} finally {
lock.unlock();
}
MycatConfig conf = MycatServer.getInstance().getConfig();
startTime = System.currentTimeMillis();
for (final RouteResultsetNode node : rrs.getNodes()) {
BackendConnection conn = session.getTarget(node);
if (session.tryExistsCon(conn, node)) {
_execute(conn, node);
} else {
// create new connection
PhysicalDBNode dn = conf.getDataNodes().get(node.getName());
dn.getConnection(dn.getDatabase(), autocommit, node, this, node);
}
}
}

不难发现,与单节点的执行过程基本是一致的,无非是打了一层循环,对每个datanode分别进行了同样的操作而已。

 


为尊重原创成果,如需转载烦请注明本文出处:

http://www.cnblogs.com/fernandolee24/p/5236237.html,特此感谢

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