Seata源码—6.Seata AT模式的数据源代理一

大纲

1.Seata的Resource资源接口源码

2.Seata数据源连接池代理的实现源码

3.Client向Server发起注册RM的源码

4.Client向Server注册RM时的交互源码

5.数据源连接代理与SQL句柄代理的初始化源码

6.Seata基于SQL句柄代理执行SQL的源码

7.执行SQL语句前取消自动提交事务的源码

8.执行SQL语句前后构建数据镜像的源码

9.构建全局锁的key和UndoLog数据的源码

10.Seata Client发起分支事务注册的源码

11.Seata Server处理分支事务注册请求的源码

12.将UndoLog写入到数据库与提交事务的源码

13.通过全局锁重试策略组件执行事务的提交

14.注册分支事务时获取全局锁的入口源码

15.Seata Server获取全局锁的具体逻辑源码

16.全局锁和分支事务及本地事务总结

17.提交全局事务以及提交各分支事务的源码

18.全局事务回滚的过程源码

1.Seata的Resource资源接口源码

数据源代理DataSourceProxy不仅实现了Seata的Resource资源接口，同时还继承了实现了SeataDataSourceProxy接口的抽象类AbstractDataSourceProxy。

由于SeataDataSourceProxy接口又继承自JDK提供的DataSource接口，所以通过数据源连接池DataSource接口的方法，可以获取数据源的连接。

注意：这里的数据源==数据库。

public class DataSourceProxy extends AbstractDataSourceProxy implements Resource {...
}public abstract class AbstractDataSourceProxy implements SeataDataSourceProxy {...
}public interface SeataDataSourceProxy extends DataSource {...
}public interface DataSource extends CommonDataSource, Wrapper {//获取数据源连接Connection getConnection() throws SQLException;Connection getConnection(String username, String password) throws SQLException;
}

Seata的Resource资源接口有三个方法：

一.getResourceGroupId()方法用来获取资源分组

比如主从节点同属一个分组。

二.getResourceId()方法用来获取数据源ID

比如数据源连接URL可作为数据源ID。

三.getBranchType()方法用来获取分支事务类型

比如类型有：AT、TCC、SAGA、XA。

//Resource that can be managed by Resource Manager and involved into global transaction.
//资源是由RM资源管理组件来负责管理的
//RM资源管理器组件会负责把一个个的资源纳入到全局事务里去
//比如RM可以管理数据库资源，把一个数据库本地事务纳入到全局事务里去
public interface Resource {//Get the resource group id.//e.g. master and slave data-source should be with the same resource group id.//获取到资源分组ID//主从架构的数据源关联到同一个资源分组ID//比如MySQL部署了主从架构，主节点和从节点是两个数据源，但是关联到一个分组IDString getResourceGroupId();//Get the resource id.//e.g. url of a data-source could be the id of the db data-source resource.//比如数据源连接URL可以作为数据源的IDString getResourceId();//get resource type, AT, TCC, SAGA and XA//branchType表示分支事务类型：AT、TCC、SAGA、XABranchType getBranchType();
}

2.Seata数据源连接池代理的实现源码

(1)Seata的数据源连接池代理接口SeataDataSourceProxy

(2)Seata的数据源连接池代理抽象类AbstractDataSourceProxy

(3)Seata的数据源连接池代理DataSourceProxy的变量和初始化

(1)Seata的数据源连接池代理接口SeataDataSourceProxy

SeataDataSourceProxy数据源代理在继承DataSource数据源连接池的基础上，增加了两个方法：一个是获取代理的目标数据源连接池的方法，一个是获取代理的目标数据源连接池对应的分支事务类型的方法。

public interface SeataDataSourceProxy extends DataSource {//Gets target data source. //获取代理的目标数据源连接池DataSource getTargetDataSource();//Gets branch type. //获取代理的目标数据源连接池对应的分支事务类型BranchType getBranchType();
}

(2)Seata的数据源连接池代理抽象类AbstractDataSourceProxy

AbstractDataSourceProxy抽象类的主要工作是封装代理的目标数据源连接池targetDataSource。

//The type Abstract data source proxy.
//AbstractDataSourceProxy主要的工作就是：
//封装了代理的目标数据源连接池targetDataSource
public abstract class AbstractDataSourceProxy implements SeataDataSourceProxy {//The Target data source.//代理目标的连接池，可以通过targetDataSource来获取连接protected DataSource targetDataSource;//Instantiates a new Abstract data source proxy.public AbstractDataSourceProxy(){ }//Instantiates a new Abstract data source proxy.public AbstractDataSourceProxy(DataSource targetDataSource) {this.targetDataSource = targetDataSource;}//Gets target data source.@Overridepublic DataSource getTargetDataSource() {return targetDataSource;}@Overridepublic <T> T unwrap(Class<T> iface) throws SQLException {return targetDataSource.unwrap(iface);}//判断目标连接池targetDataSource是否包装了指定的接口iface@Overridepublic boolean isWrapperFor(Class<?> iface) throws SQLException {return targetDataSource.isWrapperFor(iface);}@Overridepublic PrintWriter getLogWriter() throws SQLException {return targetDataSource.getLogWriter();}@Overridepublic void setLogWriter(PrintWriter out) throws SQLException {targetDataSource.setLogWriter(out);}@Overridepublic void setLoginTimeout(int seconds) throws SQLException {targetDataSource.setLoginTimeout(seconds);}@Overridepublic int getLoginTimeout() throws SQLException {return targetDataSource.getLoginTimeout();}@Overridepublic Logger getParentLogger() throws SQLFeatureNotSupportedException {return targetDataSource.getParentLogger();}
}

(3)Seata的数据源连接池代理DataSourceProxy的变量和初始化

初始化数据源连接池代理DataSourceProxy的具体逻辑是：首先从目标数据库连接池dataSource中获取一个数据库连接，然后根据这个数据库连接Connection去初始化jdbcUrl和dbType，接着根据数据库连接地址jdbcUrl初始化resourceId，然后把当前数据库连接池代理DataSourceProxy作为一个资源注册到默认的RM即DefaultResourceManager里去，最后设置RootContext上下文即线程本地变量副本中的分支事务类型。

public class DataSourceProxy extends AbstractDataSourceProxy implements Resource {private static final Logger LOGGER = LoggerFactory.getLogger(DataSourceProxy.class);//默认资源分组IDprivate static final String DEFAULT_RESOURCE_GROUP_ID = "DEFAULT";//Enable the table meta checker，默认是不启用的private static boolean ENABLE_TABLE_META_CHECKER_ENABLE = ConfigurationFactory.getInstance().getBoolean(ConfigurationKeys.CLIENT_TABLE_META_CHECK_ENABLE, DEFAULT_CLIENT_TABLE_META_CHECK_ENABLE);//Table meta checker interval，默认是60sprivate static final long TABLE_META_CHECKER_INTERVAL = ConfigurationFactory.getInstance().getLong(ConfigurationKeys.CLIENT_TABLE_META_CHECKER_INTERVAL, DEFAULT_TABLE_META_CHECKER_INTERVAL);//资源组ID，比如MySQL部署了主从架构，主节点和从节点是两个数据源，但是关联到一个分组IDprivate String resourceGroupId;//代理的目标数据源连接url，这个数据源连接url也可以作为resourceIdprivate String jdbcUrl;//数据源ID，比如数据库连接url就可以作为一个数据源IDprivate String resourceId;//数据源类型private String dbType;//数据源连接用户名private String userName;//定时调度的线程池，定时检查表里的元数据private final ScheduledExecutorService tableMetaExecutor = new ScheduledThreadPoolExecutor(1, new NamedThreadFactory("tableMetaChecker", 1, true));//Instantiates a new Data source proxy.public DataSourceProxy(DataSource targetDataSource) {this(targetDataSource, DEFAULT_RESOURCE_GROUP_ID);}//Instantiates a new Data source proxy.//@param targetDataSource the target data source//@param resourceGroupId  the resource group idpublic DataSourceProxy(DataSource targetDataSource, String resourceGroupId) {if (targetDataSource instanceof SeataDataSourceProxy) {LOGGER.info("Unwrap the target data source, because the type is: {}", targetDataSource.getClass().getName());targetDataSource = ((SeataDataSourceProxy) targetDataSource).getTargetDataSource();}this.targetDataSource = targetDataSource;init(targetDataSource, resourceGroupId);}//初始化数据源连接池代理DataSourceProxyprivate void init(DataSource dataSource, String resourceGroupId) {//资源分组IDthis.resourceGroupId = resourceGroupId;//从目标数据库连接池dataSource中，获取一个数据库连接try (Connection connection = dataSource.getConnection()) {//获取数据库连接connection里的元数据的连接urljdbcUrl = connection.getMetaData().getURL();//根据连接url获取到数据库类型dbType = JdbcUtils.getDbType(jdbcUrl);if (JdbcConstants.ORACLE.equals(dbType)) {//如果数据库类型等于oracle，则需要获取数据库连接connection的元数据的用户名userName = connection.getMetaData().getUserName();} else if (JdbcConstants.MARIADB.equals(dbType)) {//如果数据库类型等于mariadb，则需要对数据库类型进行赋值为MySQLdbType = JdbcConstants.MYSQL;}} catch (SQLException e) {throw new IllegalStateException("can not init dataSource", e);}//初始化资源ID，也就是获取数据库连接url来初始化resourceIDinitResourceId();//把当前数据库连接池代理，作为一个资源，注册到默认的RM里，也就是DefaultResourceManagerDefaultResourceManager.get().registerResource(this);if (ENABLE_TABLE_META_CHECKER_ENABLE) {tableMetaExecutor.scheduleAtFixedRate(() -> {try (Connection connection = dataSource.getConnection()) {TableMetaCacheFactory.getTableMetaCache(DataSourceProxy.this.getDbType()).refresh(connection, DataSourceProxy.this.getResourceId());} catch (Exception ignore) {}}, 0, TABLE_META_CHECKER_INTERVAL, TimeUnit.MILLISECONDS);}//Set the default branch type to 'AT' in the RootContext.//设置RootContext上下文，即线程本地变量副本中的分支事务类型RootContext.setDefaultBranchType(this.getBranchType());}private void initResourceId() {if (JdbcConstants.POSTGRESQL.equals(dbType)) {initPGResourceId();} else if (JdbcConstants.ORACLE.equals(dbType) && userName != null) {initDefaultResourceId();resourceId = resourceId + "/" + userName;} else if (JdbcConstants.MYSQL.equals(dbType)) {initMysqlResourceId();} else {initDefaultResourceId();}}private void initMysqlResourceId() {String startsWith = "jdbc:mysql:loadbalance://";if (jdbcUrl.startsWith(startsWith)) {String url;if (jdbcUrl.contains("?")) {url = jdbcUrl.substring(0, jdbcUrl.indexOf('?'));} else {url = jdbcUrl;}resourceId = url.replace(",", "|");} else {initDefaultResourceId();}}...
}

3.Client向Server发起注册RM的源码

初始化数据源连接池代理DataSourceProxy时，会将数据库连接池代理作为资源，注册到DefaultResourceManager资源管理器中。

而初始化DefaultResourceManager时，会通过SPI机制加载所有的ResourceManager。

因此在执行DataSourceProxy的init()方法进行初始化时，由于会调用DefaultResourceManager的registerResource()方法，所以最后会执行到DataSourceManager的registerResource()方法。

在DataSourceManager的registerResource()方法中，首先会把数据源连接池代理DataSourceProxy放入一个Map中进行缓存，然后通过RmNettyRemotingClient构造一个注册RM的请求把数据源连接池代理DataSourceProxy作为资源注册到Seata Server中。

public class DefaultResourceManager implements ResourceManager {//all resource managersprotected static Map<BranchType, ResourceManager> resourceManagers = new ConcurrentHashMap<>();private static class SingletonHolder {private static DefaultResourceManager INSTANCE = new DefaultResourceManager();}//Get resource manager.public static DefaultResourceManager get() {return SingletonHolder.INSTANCE;}private DefaultResourceManager() {initResourceManagers();}protected void initResourceManagers() {//init all resource managers//通过SPI加载所有的ResourceManager资源管理器//比如：DataSourceManager、TCCResourceManager、SagaResourceManager、ResourceManagerXAList<ResourceManager> allResourceManagers = EnhancedServiceLoader.loadAll(ResourceManager.class);if (CollectionUtils.isNotEmpty(allResourceManagers)) {for (ResourceManager rm : allResourceManagers) {resourceManagers.put(rm.getBranchType(), rm);}}}@Overridepublic void registerResource(Resource resource) {getResourceManager(resource.getBranchType()).registerResource(resource);}public ResourceManager getResourceManager(BranchType branchType) {ResourceManager rm = resourceManagers.get(branchType);if (rm == null) {throw new FrameworkException("No ResourceManager for BranchType:" + branchType.name());}return rm;}...
}//The type Data source manager.
//DataSourceManager是AT模式下的资源管理器
public class DataSourceManager extends AbstractResourceManager {//异步化workerprivate final AsyncWorker asyncWorker = new AsyncWorker(this);//RM负责管理的一些resource资源private final Map<String, Resource> dataSourceCache = new ConcurrentHashMap<>();...@Overridepublic void registerResource(Resource resource) {DataSourceProxy dataSourceProxy = (DataSourceProxy) resource;//根据资源ID和数据源代理，把数据源连接池代理DataSourceProxy放入到map里去dataSourceCache.put(dataSourceProxy.getResourceId(), dataSourceProxy);super.registerResource(dataSourceProxy);}...
}public abstract class AbstractResourceManager implements ResourceManager {...@Overridepublic void registerResource(Resource resource) {//通过RmNettyRemotingClient把RM注册到Seata Server中RmNettyRemotingClient.getInstance().registerResource(resource.getResourceGroupId(), resource.getResourceId());}...
}

4.Client向Server注册RM时的交互源码

(1)Client异步发送注册RM的请求给Server

(2)Server收到注册RM的请求后的处理及异步响应

(1)Client异步发送注册RM的请求给Server

public final class RmNettyRemotingClient extends AbstractNettyRemotingClient {...//Register new db key.public void registerResource(String resourceGroupId, String resourceId) {//Resource registration cannot be performed until the RM client is initializedif (StringUtils.isBlank(transactionServiceGroup)) {return;}if (getClientChannelManager().getChannels().isEmpty()) {getClientChannelManager().reconnect(transactionServiceGroup);return;}synchronized (getClientChannelManager().getChannels()) {//向每一个Server发起注册for (Map.Entry<String, Channel> entry : getClientChannelManager().getChannels().entrySet()) {String serverAddress = entry.getKey();Channel rmChannel = entry.getValue();if (LOGGER.isInfoEnabled()) {LOGGER.info("will register resourceId:{}", resourceId);}sendRegisterMessage(serverAddress, rmChannel, resourceId);}}}public void sendRegisterMessage(String serverAddress, Channel channel, String resourceId) {RegisterRMRequest message = new RegisterRMRequest(applicationId, transactionServiceGroup);message.setResourceIds(resourceId);try {//异步发送注册RM的请求super.sendAsyncRequest(channel, message);} catch (FrameworkException e) {if (e.getErrcode() == FrameworkErrorCode.ChannelIsNotWritable && serverAddress != null) {getClientChannelManager().releaseChannel(channel, serverAddress);if (LOGGER.isInfoEnabled()) {LOGGER.info("remove not writable channel:{}", channel);}} else {LOGGER.error("register resource failed, channel:{},resourceId:{}", channel, resourceId, e);}}}...
}public abstract class AbstractNettyRemotingClient extends AbstractNettyRemoting implements RemotingClient {...@Overridepublic void sendAsyncRequest(Channel channel, Object msg) {if (channel == null) {LOGGER.warn("sendAsyncRequest nothing, caused by null channel.");return;}RpcMessage rpcMessage = buildRequestMessage(msg, msg instanceof HeartbeatMessage? ProtocolConstants.MSGTYPE_HEARTBEAT_REQUEST: ProtocolConstants.MSGTYPE_RESQUEST_ONEWAY);if (rpcMessage.getBody() instanceof MergeMessage) {mergeMsgMap.put(rpcMessage.getId(), (MergeMessage) rpcMessage.getBody());}super.sendAsync(channel, rpcMessage);}...
}public abstract class AbstractNettyRemoting implements Disposable {...//rpc async request.protected void sendAsync(Channel channel, RpcMessage rpcMessage) {channelWritableCheck(channel, rpcMessage.getBody());if (LOGGER.isDebugEnabled()) {LOGGER.debug("write message:" + rpcMessage.getBody() + ", channel:" + channel + ",active?" + channel.isActive() + ",writable?" + channel.isWritable() + ",isopen?" + channel.isOpen());}doBeforeRpcHooks(ChannelUtil.getAddressFromChannel(channel), rpcMessage);channel.writeAndFlush(rpcMessage).addListener((ChannelFutureListener) future -> {if (!future.isSuccess()) {destroyChannel(future.channel());}});}...
}

(2)Server收到注册RM的请求后的处理及异步响应

public abstract class AbstractNettyRemotingServer extends AbstractNettyRemoting implements RemotingServer {...@ChannelHandler.Sharableclass ServerHandler extends ChannelDuplexHandler {@Overridepublic void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {if (!(msg instanceof RpcMessage)) {return;}//接下来调用processMessage()方法对解码完毕的RpcMessage对象进行处理processMessage(ctx, (RpcMessage) msg);}...}...
}public abstract class AbstractNettyRemoting implements Disposable {...//Rpc message processing.protected void processMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {if (LOGGER.isDebugEnabled()) {LOGGER.debug(String.format("%s msgId:%s, body:%s", this, rpcMessage.getId(), rpcMessage.getBody()));}Object body = rpcMessage.getBody();if (body instanceof MessageTypeAware) {MessageTypeAware messageTypeAware = (MessageTypeAware) body;//根据消息类型获取到一个Pair对象，该Pair对象是由请求处理组件和请求处理线程池组成的//processorTable里的内容，是NettyRemotingServer在初始化时，通过调用registerProcessor()方法put进去的final Pair<RemotingProcessor, ExecutorService> pair = this.processorTable.get((int) messageTypeAware.getTypeCode());if (pair != null) {if (pair.getSecond() != null) {try {pair.getSecond().execute(() -> {try {pair.getFirst().process(ctx, rpcMessage);} catch (Throwable th) {LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);} finally {MDC.clear();}});} catch (RejectedExecutionException e) {...}} else {try {pair.getFirst().process(ctx, rpcMessage);} catch (Throwable th) {LOGGER.error(FrameworkErrorCode.NetDispatch.getErrCode(), th.getMessage(), th);}}} else {LOGGER.error("This message type [{}] has no processor.", messageTypeAware.getTypeCode());}} else {LOGGER.error("This rpcMessage body[{}] is not MessageTypeAware type.", body);}}...
}public class RegRmProcessor implements RemotingProcessor {...@Overridepublic void process(ChannelHandlerContext ctx, RpcMessage rpcMessage) throws Exception {onRegRmMessage(ctx, rpcMessage);}private void onRegRmMessage(ChannelHandlerContext ctx, RpcMessage rpcMessage) {RegisterRMRequest message = (RegisterRMRequest) rpcMessage.getBody();//获取请求的发送地址String ipAndPort = NetUtil.toStringAddress(ctx.channel().remoteAddress());boolean isSuccess = false;String errorInfo = StringUtils.EMPTY;try {if (null == checkAuthHandler || checkAuthHandler.regResourceManagerCheckAuth(message)) {//通过Channel管理组件ChannelManager，注册RM网络连接ChannelManager.registerRMChannel(message, ctx.channel());Version.putChannelVersion(ctx.channel(), message.getVersion());isSuccess = true;if (LOGGER.isDebugEnabled()) {LOGGER.debug("RM checkAuth for client:{},vgroup:{},applicationId:{} is OK", ipAndPort, message.getTransactionServiceGroup(), message.getApplicationId());}} else {if (LOGGER.isWarnEnabled()) {LOGGER.warn("RM checkAuth for client:{},vgroup:{},applicationId:{} is FAIL", ipAndPort, message.getTransactionServiceGroup(), message.getApplicationId());}}} catch (Exception exx) {isSuccess = false;errorInfo = exx.getMessage();LOGGER.error("RM register fail, error message:{}", errorInfo);}RegisterRMResponse response = new RegisterRMResponse(isSuccess);if (StringUtils.isNotEmpty(errorInfo)) {response.setMsg(errorInfo);}//返回响应给客户端remotingServer.sendAsyncResponse(rpcMessage, ctx.channel(), response);if (isSuccess && LOGGER.isInfoEnabled()) {LOGGER.info("RM register success,message:{},channel:{},client version:{}", message, ctx.channel(), message.getVersion());}}...
}public class ChannelManager {...public static void registerRMChannel(RegisterRMRequest resourceManagerRequest, Channel channel) throws IncompatibleVersionException {Version.checkVersion(resourceManagerRequest.getVersion());Set<String> dbkeySet = dbKeytoSet(resourceManagerRequest.getResourceIds());RpcContext rpcContext;if (!IDENTIFIED_CHANNELS.containsKey(channel)) {rpcContext = buildChannelHolder(NettyPoolKey.TransactionRole.RMROLE, resourceManagerRequest.getVersion(),resourceManagerRequest.getApplicationId(), resourceManagerRequest.getTransactionServiceGroup(),resourceManagerRequest.getResourceIds(), channel);rpcContext.holdInIdentifiedChannels(IDENTIFIED_CHANNELS);} else {rpcContext = IDENTIFIED_CHANNELS.get(channel);rpcContext.addResources(dbkeySet);}if (dbkeySet == null || dbkeySet.isEmpty()) { return; }for (String resourceId : dbkeySet) {String clientIp;ConcurrentMap<Integer, RpcContext> portMap =CollectionUtils.computeIfAbsent(RM_CHANNELS, resourceId, key -> new ConcurrentHashMap<>()).computeIfAbsent(resourceManagerRequest.getApplicationId(), key -> new ConcurrentHashMap<>()).computeIfAbsent(clientIp = ChannelUtil.getClientIpFromChannel(channel), key -> new ConcurrentHashMap<>());rpcContext.holdInResourceManagerChannels(resourceId, portMap);updateChannelsResource(resourceId, clientIp, resourceManagerRequest.getApplicationId());}}...
}public abstract class AbstractNettyRemotingServer extends AbstractNettyRemoting implements RemotingServer {...@Overridepublic void sendAsyncResponse(RpcMessage rpcMessage, Channel channel, Object msg) {Channel clientChannel = channel;if (!(msg instanceof HeartbeatMessage)) {clientChannel = ChannelManager.getSameClientChannel(channel);}if (clientChannel != null) {RpcMessage rpcMsg = buildResponseMessage(rpcMessage, msg, msg instanceof HeartbeatMessage? ProtocolConstants.MSGTYPE_HEARTBEAT_RESPONSE : ProtocolConstants.MSGTYPE_RESPONSE);super.sendAsync(clientChannel, rpcMsg);} else {throw new RuntimeException("channel is error.");}}...
}public abstract class AbstractNettyRemoting implements Disposable {...//rpc async request.protected void sendAsync(Channel channel, RpcMessage rpcMessage) {channelWritableCheck(channel, rpcMessage.getBody());if (LOGGER.isDebugEnabled()) {LOGGER.debug("write message:" + rpcMessage.getBody() + ", channel:" + channel + ",active?" + channel.isActive() + ",writable?" + channel.isWritable() + ",isopen?" + channel.isOpen());}doBeforeRpcHooks(ChannelUtil.getAddressFromChannel(channel), rpcMessage);channel.writeAndFlush(rpcMessage).addListener((ChannelFutureListener) future -> {if (!future.isSuccess()) {destroyChannel(future.channel());}});}...
}

5.数据源连接代理与SQL句柄代理的初始化源码

(1)数据库操作的三剑客之连接、句柄和结果

(2)数据源连接代理的初始化

(3)数据源连接代理对SQL进行预编译

(4)SQL句柄代理的初始化

(5)SQL句柄代理执行SQL

(1)数据库操作的三剑客之连接、句柄和结果

Seata Client或者Seata Server进行数据库操作的大致流程如下所示：

public class LogStoreDataBaseDAO implements LogStore {//The Log store data source. 数据源连接池protected DataSource logStoreDataSource = null;...@Overridepublic GlobalTransactionDO queryGlobalTransactionDO(long transactionId) {String sql = LogStoreSqlsFactory.getLogStoreSqls(dbType).getQueryGlobalTransactionSQLByTransactionId(globalTable);Connection conn = null;//连接PreparedStatement ps = null;//句柄ResultSet rs = null;//结果try {//1.从数据源连接池中获取数据源连接conn = logStoreDataSource.getConnection();conn.setAutoCommit(true);//2.对sql语句进行预编译ps = conn.prepareStatement(sql);ps.setLong(1, transactionId);//3.执行sql语句rs = ps.executeQuery();if (rs.next()) {return convertGlobalTransactionDO(rs);} else {return null;}} catch (SQLException e) {throw new DataAccessException(e);} finally {IOUtil.close(rs, ps, conn);}}...
}

(2)数据源连接代理的初始化

Seata Client或者Seata Server进行数据库操作时，首先会通过数据库连接池代理DataSourceProxy获取数据库连接，也就是会通过DataSourceProxy的getConnection()方法获取数据源连接代理ConnectionProxy，其中就会根据获取到的一个数据源连接Connection初始化一个数据源连接代理ConnectionProxy。

public class DataSourceProxy extends AbstractDataSourceProxy implements Resource {...@Overridepublic ConnectionProxy getConnection() throws SQLException {//从目标数据源连接池中获取一个数据库连接，然后封装到ConnectionProxy数据源连接代理中，并进行返回Connection targetConnection = targetDataSource.getConnection();return new ConnectionProxy(this, targetConnection);}@Overridepublic ConnectionProxy getConnection(String username, String password) throws SQLException {//从目标数据源连接池中获取一个数据库连接，然后封装到ConnectionProxy数据源连接代理中，并进行返回Connection targetConnection = targetDataSource.getConnection(username, password);return new ConnectionProxy(this, targetConnection);}...
}public class ConnectionProxy extends AbstractConnectionProxy {//Instantiates a new Connection proxy.public ConnectionProxy(DataSourceProxy dataSourceProxy, Connection targetConnection) {super(dataSourceProxy, targetConnection);}...
}public abstract class AbstractConnectionProxy implements Connection {//The Data source proxy. 数据源连接池代理protected DataSourceProxy dataSourceProxy;//The Target connection. 目标数据源连接protected Connection targetConnection;//Instantiates a new Abstract connection proxy.public AbstractConnectionProxy(DataSourceProxy dataSourceProxy, Connection targetConnection) {this.dataSourceProxy = dataSourceProxy;this.targetConnection = targetConnection;}...
}

(3)数据源连接代理对SQL进行预编译

数据源连接代理ConnectionProxy在进行数据库操作时，获取到数据库连接Connection之后，就需要对要执行的SQL进行预编译，也就是会调用AbstractConnectionProxy的prepareStatement()方法。

public abstract class AbstractConnectionProxy implements Connection {...//对SQL进行预编译@Overridepublic PreparedStatement prepareStatement(String sql) throws SQLException {String dbType = getDbType();//support oracle 10.2+PreparedStatement targetPreparedStatement = null;//如果是AT模式if (BranchType.AT == RootContext.getBranchType()) {List<SQLRecognizer> sqlRecognizers = SQLVisitorFactory.get(sql, dbType);if (sqlRecognizers != null && sqlRecognizers.size() == 1) {SQLRecognizer sqlRecognizer = sqlRecognizers.get(0);if (sqlRecognizer != null && sqlRecognizer.getSQLType() == SQLType.INSERT) {TableMeta tableMeta = TableMetaCacheFactory.getTableMetaCache(dbType).getTableMeta(getTargetConnection(),sqlRecognizer.getTableName(), getDataSourceProxy().getResourceId());String[] pkNameArray = new String[tableMeta.getPrimaryKeyOnlyName().size()];tableMeta.getPrimaryKeyOnlyName().toArray(pkNameArray);targetPreparedStatement = getTargetConnection().prepareStatement(sql, pkNameArray);}}}if (targetPreparedStatement == null) {targetPreparedStatement = getTargetConnection().prepareStatement(sql);}//返回一个SQL句柄代理return new PreparedStatementProxy(this, targetPreparedStatement, sql);}...
}

(4)SQL句柄代理的初始化

SQL句柄代理PreparedStatementProxy的初始化主要是设置目标SQL、目标句柄和数据源连接代理。

public class PreparedStatementProxy extends AbstractPreparedStatementProxy implements PreparedStatement, ParametersHolder {//Instantiates a new Prepared statement proxy.public PreparedStatementProxy(AbstractConnectionProxy connectionProxy, PreparedStatement targetStatement, String targetSQL) throws SQLException {super(connectionProxy, targetStatement, targetSQL);}...
}public abstract class AbstractPreparedStatementProxy extends StatementProxy<PreparedStatement> implements PreparedStatement {protected Map<Integer, ArrayList<Object>> parameters;private void initParameterHolder() {this.parameters = new HashMap<>();}//Instantiates a new Abstract prepared statement proxy.public AbstractPreparedStatementProxy(AbstractConnectionProxy connectionProxy, PreparedStatement targetStatement, String targetSQL) throws SQLException {super(connectionProxy, targetStatement, targetSQL);initParameterHolder();}...
}public class StatementProxy<T extends Statement> extends AbstractStatementProxy<T> {//Instantiates a new Statement proxy.public StatementProxy(AbstractConnectionProxy connectionWrapper, T targetStatement, String targetSQL) throws SQLException {super(connectionWrapper, targetStatement, targetSQL);}...
}public abstract class AbstractStatementProxy<T extends Statement> implements Statement {//The Connection proxy.protected AbstractConnectionProxy connectionProxy;//The Target statement.protected T targetStatement;//The Target sql.protected String targetSQL;...//Instantiates a new Abstract statement proxy.public AbstractStatementProxy(AbstractConnectionProxy connectionProxy, T targetStatement, String targetSQL) throws SQLException {this.connectionProxy = connectionProxy;this.targetStatement = targetStatement;this.targetSQL = targetSQL;}...
}

(5)SQL句柄代理执行SQL

从数据源连接池中获取到数据源连接，以及对SQL语句进行预编译后，就可以调用SQL句柄代理PreparedStatementProxy的executeQuery()等方法执行SQL语句。

6.Seata基于SQL句柄代理执行SQL的源码

(1)Spring的JdbcTemplate操作数据库的三剑客

(2)基于SQL句柄代理执行SQL的流程

(1)Spring的JdbcTemplate操作数据库的三剑客

连接、句柄和结果。

@Disabled
public class LocalTransactionWithGlobalLockDataSourceBasicTest {private static ClassPathXmlApplicationContext context;private static JdbcTemplate jdbcTemplate;@BeforeAllpublic static void before() {context = new ClassPathXmlApplicationContext("basic-test-context.xml");jdbcTemplate = (JdbcTemplate) context.getBean("jdbcTemplate");}@Testpublic void testInsert() {RootContext.bindGlobalLockFlag();jdbcTemplate.update("insert into user0 (id, name, gmt) values (?, ?, ?)", new Object[]{2, "xxx", new Date()});}...
}public class JdbcTemplate extends JdbcAccessor implements JdbcOperations {...@Overridepublic int update(String sql, @Nullable Object... args) throws DataAccessException {return update(sql, newArgPreparedStatementSetter(args));}@Overridepublic int update(String sql, @Nullable PreparedStatementSetter pss) throws DataAccessException {return update(new SimplePreparedStatementCreator(sql), pss);}protected int update(final PreparedStatementCreator psc, @Nullable final PreparedStatementSetter pss) throws DataAccessException {logger.debug("Executing prepared SQL update");return updateCount(execute(psc, ps -> {try {if (pss != null) {pss.setValues(ps);}//PreparedStatement执行SQLint rows = ps.executeUpdate();if (logger.isTraceEnabled()) {logger.trace("SQL update affected " + rows + " rows");}return rows;} finally {if (pss instanceof ParameterDisposer) {((ParameterDisposer) pss).cleanupParameters();}}}, true));}@Nullableprivate <T> T execute(PreparedStatementCreator psc, PreparedStatementCallback<T> action, boolean closeResources) throws DataAccessException {Assert.notNull(psc, "PreparedStatementCreator must not be null");Assert.notNull(action, "Callback object must not be null");if (logger.isDebugEnabled()) {String sql = getSql(psc);logger.debug("Executing prepared SQL statement" + (sql != null ? " [" + sql + "]" : ""));}//1.获取连接Connection con = DataSourceUtils.getConnection(obtainDataSource());PreparedStatement ps = null;try {//2.创建句柄ps = psc.createPreparedStatement(con);applyStatementSettings(ps);//3.执行SQL的结果T result = action.doInPreparedStatement(ps);handleWarnings(ps);return result;} catch (SQLException ex) {if (psc instanceof ParameterDisposer) {((ParameterDisposer) psc).cleanupParameters();}String sql = getSql(psc);psc = null;JdbcUtils.closeStatement(ps);ps = null;DataSourceUtils.releaseConnection(con, getDataSource());con = null;throw translateException("PreparedStatementCallback", sql, ex);} finally {if (closeResources) {if (psc instanceof ParameterDisposer) {((ParameterDisposer) psc).cleanupParameters();}JdbcUtils.closeStatement(ps);DataSourceUtils.releaseConnection(con, getDataSource());}}}...
}

(2)基于SQL句柄代理执行SQL的流程

SQL句柄代理PreparedStatementProxy在调用execute()方法执行SQL时，就会调用到ExecuteTemplate执行模版的execute()方法。

而ExecuteTemplate执行模版的execute()方法，如果发现不需要全局锁 + 没有开启全局事务，那么就普通执行本地事务。否则，最终就会调用到BaseTransactionalExecutor的excute()方法。

在BaseTransactionalExecutor的excute()方法中，首先会从线程本地变量副本中获取xid，然后再执行SQL。

public class PreparedStatementProxy extends AbstractPreparedStatementProxy implements PreparedStatement, ParametersHolder {...@Overridepublic boolean execute() throws SQLException {return ExecuteTemplate.execute(this, (statement, args) -> statement.execute());}@Overridepublic ResultSet executeQuery() throws SQLException {return ExecuteTemplate.execute(this, (statement, args) -> statement.executeQuery());}@Overridepublic int executeUpdate() throws SQLException {return ExecuteTemplate.execute(this, (statement, args) -> statement.executeUpdate());}...
}public class ExecuteTemplate {...public static <T, S extends Statement> T execute(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, Object... args) throws SQLException {return execute(null, statementProxy, statementCallback, args);}public static <T, S extends Statement> T execute(List<SQLRecognizer> sqlRecognizers, StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, Object... args) throws SQLException {//如果发现不需要全局锁，而且没有开启AT模式下的全局事务，那么就普通执行本地事务if (!RootContext.requireGlobalLock() && BranchType.AT != RootContext.getBranchType()) {//Just work as original statementreturn statementCallback.execute(statementProxy.getTargetStatement(), args);}//获取到DB的类型String dbType = statementProxy.getConnectionProxy().getDbType();if (CollectionUtils.isEmpty(sqlRecognizers)) {sqlRecognizers = SQLVisitorFactory.get(statementProxy.getTargetSQL(), dbType);}Executor<T> executor;if (CollectionUtils.isEmpty(sqlRecognizers)) {executor = new PlainExecutor<>(statementProxy, statementCallback);} else {if (sqlRecognizers.size() == 1) {SQLRecognizer sqlRecognizer = sqlRecognizers.get(0);switch (sqlRecognizer.getSQLType()) {case INSERT://通过SPI机制加载InsertExecutorexecutor = EnhancedServiceLoader.load(InsertExecutor.class, dbType, new Class[]{StatementProxy.class, StatementCallback.class, SQLRecognizer.class}, new Object[]{statementProxy, statementCallback, sqlRecognizer});break;case UPDATE:executor = new UpdateExecutor<>(statementProxy, statementCallback, sqlRecognizer);break;case DELETE:executor = new DeleteExecutor<>(statementProxy, statementCallback, sqlRecognizer);break;case SELECT_FOR_UPDATE:executor = new SelectForUpdateExecutor<>(statementProxy, statementCallback, sqlRecognizer);break;case INSERT_ON_DUPLICATE_UPDATE:switch (dbType) {case JdbcConstants.MYSQL:case JdbcConstants.MARIADB:executor = new MySQLInsertOrUpdateExecutor(statementProxy, statementCallback, sqlRecognizer);break;default:throw new NotSupportYetException(dbType + " not support to INSERT_ON_DUPLICATE_UPDATE");}break;default:executor = new PlainExecutor<>(statementProxy, statementCallback);break;}} else {executor = new MultiExecutor<>(statementProxy, statementCallback, sqlRecognizers);}}T rs;try {//比如下面最终会调用BaseTransactionalExecutor.excute()方法rs = executor.execute(args);} catch (Throwable ex) {if (!(ex instanceof SQLException)) {// Turn other exception into SQLExceptionex = new SQLException(ex);}throw (SQLException) ex;}return rs;}...
}@LoadLevel(name = JdbcConstants.MYSQL, scope = Scope.PROTOTYPE)
public class MySQLInsertExecutor extends BaseInsertExecutor implements Defaultable {...//Instantiates a new Abstract dml base executor.public MySQLInsertExecutor(StatementProxy statementProxy, StatementCallback statementCallback, SQLRecognizer sqlRecognizer) {super(statementProxy, statementCallback, sqlRecognizer);}...
}public abstract class BaseInsertExecutor<T, S extends Statement> extends AbstractDMLBaseExecutor<T, S> implements InsertExecutor<T> {...public BaseInsertExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, SQLRecognizer sqlRecognizer) {super(statementProxy, statementCallback, sqlRecognizer);}...
}public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {...public AbstractDMLBaseExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, SQLRecognizer sqlRecognizer) {super(statementProxy, statementCallback, sqlRecognizer);}@Overridepublic T doExecute(Object... args) throws Throwable {AbstractConnectionProxy connectionProxy = statementProxy.getConnectionProxy();//判断是否是自动提交本地事务，默认情况本地事务都是自动提交的，此时需要阻止自动提交if (connectionProxy.getAutoCommit()) {return executeAutoCommitTrue(args);} else {return executeAutoCommitFalse(args);}}...
}public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {//The Statement proxy.protected StatementProxy<S> statementProxy;//The Statement callback.protected StatementCallback<T, S> statementCallback;//The Sql recognizer.protected SQLRecognizer sqlRecognizer;...public BaseTransactionalExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback,SQLRecognizer sqlRecognizer) {this.statementProxy = statementProxy;this.statementCallback = statementCallback;this.sqlRecognizer = sqlRecognizer;}...@Overridepublic T execute(Object... args) throws Throwable {//获取xidString xid = RootContext.getXID();if (xid != null) {statementProxy.getConnectionProxy().bind(xid);}statementProxy.getConnectionProxy().setGlobalLockRequire(RootContext.requireGlobalLock());return doExecute(args);}//Do execute object.protected abstract T doExecute(Object... args) throws Throwable;...
}

7.执行SQL语句前取消自动提交事务的源码

执行ExecuteTemplate执行模版的execute()方法时，最终会调用到BaseTransactionalExecutor基础事务执行器的excute()方法。

执行BaseTransactionalExecutor的execute()方法时，又会执行到AbstractDMLBaseExecutor的doExecute()方法。该方法会判断目标数据库连接是否会自动提交本地事务，默认情况下本地事务都是自动提交的。如果是，则取消自动提交本地事务。

public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {//The Statement proxy.protected StatementProxy<S> statementProxy;//The Statement callback.protected StatementCallback<T, S> statementCallback;//The Sql recognizer.protected SQLRecognizer sqlRecognizer;...public BaseTransactionalExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback,SQLRecognizer sqlRecognizer) {this.statementProxy = statementProxy;this.statementCallback = statementCallback;this.sqlRecognizer = sqlRecognizer;}...@Overridepublic T execute(Object... args) throws Throwable {//获取xidString xid = RootContext.getXID();if (xid != null) {statementProxy.getConnectionProxy().bind(xid);}statementProxy.getConnectionProxy().setGlobalLockRequire(RootContext.requireGlobalLock());return doExecute(args);}//Do execute object.protected abstract T doExecute(Object... args) throws Throwable;...
}public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {...public AbstractDMLBaseExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, SQLRecognizer sqlRecognizer) {super(statementProxy, statementCallback, sqlRecognizer);}@Overridepublic T doExecute(Object... args) throws Throwable {AbstractConnectionProxy connectionProxy = statementProxy.getConnectionProxy();//判断是否是自动提交本地事务，默认情况本地事务都是自动提交的，此时需要阻止自动提交if (connectionProxy.getAutoCommit()) {return executeAutoCommitTrue(args);} else {return executeAutoCommitFalse(args);}}...
}public abstract class AbstractConnectionProxy implements Connection {...@Overridepublic boolean getAutoCommit() throws SQLException {//判断目标数据库连接是否是自动提交，默认情况是都是自动提交的return targetConnection.getAutoCommit();}...
}public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {...//Execute auto commit true t.protected T executeAutoCommitTrue(Object[] args) throws Throwable {ConnectionProxy connectionProxy = statementProxy.getConnectionProxy();try {//修改自动提交事务的设置，此时需要阻止自动提交事务connectionProxy.changeAutoCommit();return new LockRetryPolicy(connectionProxy).execute(() -> {T result = executeAutoCommitFalse(args);//执行SQL语句connectionProxy.commit();//手动提交本地事务return result;});} catch (Exception e) {//when exception occur in finally,this exception will lost, so just print it hereLOGGER.error("execute executeAutoCommitTrue error:{}", e.getMessage(), e);if (!LockRetryPolicy.isLockRetryPolicyBranchRollbackOnConflict()) {connectionProxy.getTargetConnection().rollback();}throw e;} finally {connectionProxy.getContext().reset();connectionProxy.setAutoCommit(true);}}...
}public class ConnectionProxy extends AbstractConnectionProxy {private final ConnectionContext context = new ConnectionContext();...//change connection autoCommit to false by seatapublic void changeAutoCommit() throws SQLException {getContext().setAutoCommitChanged(true);setAutoCommit(false);}//Gets context.public ConnectionContext getContext() {return context;}@Overridepublic void setAutoCommit(boolean autoCommit) throws SQLException {if ((context.inGlobalTransaction() || context.isGlobalLockRequire()) && autoCommit && !getAutoCommit()) {//change autocommit from false to true, we should commit() first according to JDBC spec.doCommit();}//把目标数据源连接的自动提交事务设置为falsetargetConnection.setAutoCommit(autoCommit);}...
}

8.执行SQL语句前后构建数据镜像的源码

(1)AbstractDMLBaseExecutor的doExecute()方法的执行流程

(2)以UpdateExecuto为例构建前后镜像

(1)AbstractDMLBaseExecutor的doExecute()方法的执行流程

一.首先设置数据源连接阻止其自动提交事务

二.根据目标SQL语句构建beforeImage前镜像

三.执行目标SQL语句(但还没提交其对应的事务)

四.根据beforeImage前镜像构建afterImage后镜像

五.根据前镜像和后镜像构建UndoLog数据

六.手动提交数据源连接代理的事务

public abstract class AbstractDMLBaseExecutor<T, S extends Statement> extends BaseTransactionalExecutor<T, S> {...//Execute auto commit true t.protected T executeAutoCommitTrue(Object[] args) throws Throwable {ConnectionProxy connectionProxy = statementProxy.getConnectionProxy();try {//修改数据源连接的自动提交事务的设置，此时需要阻止自动提交事务connectionProxy.changeAutoCommit();return new LockRetryPolicy(connectionProxy).execute(() -> {T result = executeAutoCommitFalse(args);//执行SQL语句connectionProxy.commit();//手动提交本地事务return result;});} catch (Exception e) {// when exception occur in finally,this exception will lost, so just print it hereLOGGER.error("execute executeAutoCommitTrue error:{}", e.getMessage(), e);if (!LockRetryPolicy.isLockRetryPolicyBranchRollbackOnConflict()) {connectionProxy.getTargetConnection().rollback();}throw e;} finally {connectionProxy.getContext().reset();connectionProxy.setAutoCommit(true);}}//Execute auto commit false t.protected T executeAutoCommitFalse(Object[] args) throws Exception {if (!JdbcConstants.MYSQL.equalsIgnoreCase(getDbType()) && isMultiPk()) {throw new NotSupportYetException("multi pk only support mysql!");}//根据目标SQL语句构建beforeImage，表示目标SQL执行前的数据镜像TableRecords beforeImage = beforeImage();//接下来真正去执行这条SQL语句，但是此时本地事务还不会提交T result = statementCallback.execute(statementProxy.getTargetStatement(), args);int updateCount = statementProxy.getUpdateCount();if (updateCount > 0) {//根据beforeImage构建afterImage，表示目标SQL执行后的数据镜像TableRecords afterImage = afterImage(beforeImage);//根据beforeImage和afterImage准备undoLog数据到数据源连接代理中prepareUndoLog(beforeImage, afterImage);}return result;}...
}

(2)以UpdateExecutor为例构建前后镜像

public class TableRecords implements java.io.Serializable {//表的元数据private transient TableMeta tableMeta;//表的名称private String tableName;//表的多行数据private List<Row> rows = new ArrayList<Row>();...
}public class UpdateExecutor<T, S extends Statement> extends AbstractDMLBaseExecutor<T, S> {private static final Configuration CONFIG = ConfigurationFactory.getInstance();private static final boolean ONLY_CARE_UPDATE_COLUMNS = CONFIG.getBoolean(ConfigurationKeys.TRANSACTION_UNDO_ONLY_CARE_UPDATE_COLUMNS, DefaultValues.DEFAULT_ONLY_CARE_UPDATE_COLUMNS);//Instantiates a new Update executor.public UpdateExecutor(StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, SQLRecognizer sqlRecognizer) {super(statementProxy, statementCallback, sqlRecognizer);}@Overrideprotected TableRecords beforeImage() throws SQLException {ArrayList<List<Object>> paramAppenderList = new ArrayList<>();TableMeta tmeta = getTableMeta();//根据主键ID值拼接一个SQL语句，查询这条数据更新前的镜像String selectSQL = buildBeforeImageSQL(tmeta, paramAppenderList);return buildTableRecords(tmeta, selectSQL, paramAppenderList);}private String buildBeforeImageSQL(TableMeta tableMeta, ArrayList<List<Object>> paramAppenderList) {SQLUpdateRecognizer recognizer = (SQLUpdateRecognizer) sqlRecognizer;List<String> updateColumns = recognizer.getUpdateColumns();StringBuilder prefix = new StringBuilder("SELECT ");StringBuilder suffix = new StringBuilder(" FROM ").append(getFromTableInSQL());String whereCondition = buildWhereCondition(recognizer, paramAppenderList);String orderByCondition = buildOrderCondition(recognizer, paramAppenderList);String limitCondition = buildLimitCondition(recognizer, paramAppenderList);if (StringUtils.isNotBlank(whereCondition)) {suffix.append(WHERE).append(whereCondition);}if (StringUtils.isNotBlank(orderByCondition)) {suffix.append(" ").append(orderByCondition);}if (StringUtils.isNotBlank(limitCondition)) {suffix.append(" ").append(limitCondition);}suffix.append(" FOR UPDATE");StringJoiner selectSQLJoin = new StringJoiner(", ", prefix.toString(), suffix.toString());if (ONLY_CARE_UPDATE_COLUMNS) {if (!containsPK(updateColumns)) {selectSQLJoin.add(getColumnNamesInSQL(tableMeta.getEscapePkNameList(getDbType())));}for (String columnName : updateColumns) {selectSQLJoin.add(columnName);}//The on update xxx columns will be auto update by db, so it's also the actually updated columnsList<String> onUpdateColumns = tableMeta.getOnUpdateColumnsOnlyName();onUpdateColumns.removeAll(updateColumns);for (String onUpdateColumn : onUpdateColumns) {selectSQLJoin.add(ColumnUtils.addEscape(onUpdateColumn, getDbType()));}} else {for (String columnName : tableMeta.getAllColumns().keySet()) {selectSQLJoin.add(ColumnUtils.addEscape(columnName, getDbType()));}}return selectSQLJoin.toString();}@Overrideprotected TableRecords afterImage(TableRecords beforeImage) throws SQLException {TableMeta tmeta = getTableMeta();if (beforeImage == null || beforeImage.size() == 0) {return TableRecords.empty(getTableMeta());}String selectSQL = buildAfterImageSQL(tmeta, beforeImage);ResultSet rs = null;try (PreparedStatement pst = statementProxy.getConnection().prepareStatement(selectSQL)) {SqlGenerateUtils.setParamForPk(beforeImage.pkRows(), getTableMeta().getPrimaryKeyOnlyName(), pst);rs = pst.executeQuery();return TableRecords.buildRecords(tmeta, rs);} finally {IOUtil.close(rs);}}private String buildAfterImageSQL(TableMeta tableMeta, TableRecords beforeImage) throws SQLException {StringBuilder prefix = new StringBuilder("SELECT ");String whereSql = SqlGenerateUtils.buildWhereConditionByPKs(tableMeta.getPrimaryKeyOnlyName(), beforeImage.pkRows().size(), getDbType());String suffix = " FROM " + getFromTableInSQL() + " WHERE " + whereSql;StringJoiner selectSQLJoiner = new StringJoiner(", ", prefix.toString(), suffix);if (ONLY_CARE_UPDATE_COLUMNS) {SQLUpdateRecognizer recognizer = (SQLUpdateRecognizer) sqlRecognizer;List<String> updateColumns = recognizer.getUpdateColumns();if (!containsPK(updateColumns)) {selectSQLJoiner.add(getColumnNamesInSQL(tableMeta.getEscapePkNameList(getDbType())));}for (String columnName : updateColumns) {selectSQLJoiner.add(columnName);}//The on update xxx columns will be auto update by db, so it's also the actually updated columnsList<String> onUpdateColumns = tableMeta.getOnUpdateColumnsOnlyName();onUpdateColumns.removeAll(updateColumns);for (String onUpdateColumn : onUpdateColumns) {selectSQLJoiner.add(ColumnUtils.addEscape(onUpdateColumn, getDbType()));}} else {for (String columnName : tableMeta.getAllColumns().keySet()) {selectSQLJoiner.add(ColumnUtils.addEscape(columnName, getDbType()));}}return selectSQLJoiner.toString();}
}

9.构建全局锁的key和UndoLog数据的源码

(1)prepareUndoLog()方法会构建全局锁的key和UndoLog数据

(2)构建全局锁的key的源码

(3)构建UndoLog数据的源码

(1)prepareUndoLog()方法会构建全局锁的key和UndoLog数据

在基础事务执行器BaseTransactionalExecutor的prepareUndoLog()方法中，会构建全局锁的key和构建UndoLog数据，并把它们设置到数据源连接代理ConnectionProxy中。

public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {...//prepare undo log.//@param beforeImage the before image//@param afterImage  the after imageprotected void prepareUndoLog(TableRecords beforeImage, TableRecords afterImage) throws SQLException {if (beforeImage.getRows().isEmpty() && afterImage.getRows().isEmpty()) {return;}if (SQLType.UPDATE == sqlRecognizer.getSQLType()) {if (beforeImage.getRows().size() != afterImage.getRows().size()) {throw new ShouldNeverHappenException("Before image size is not equaled to after image size, probably because you updated the primary keys.");}}ConnectionProxy connectionProxy = statementProxy.getConnectionProxy();TableRecords lockKeyRecords = sqlRecognizer.getSQLType() == SQLType.DELETE ? beforeImage : afterImage;//构建全局锁的key//比如更新了一批数据，那么需要针对这批数据的主键ID，来构建这批数据的全局锁的keyString lockKeys = buildLockKey(lockKeyRecords);if (null != lockKeys) {//将全局锁key设置到数据源连接代理ConnectionProxy中connectionProxy.appendLockKey(lockKeys);//构建UndoLogSQLUndoLog sqlUndoLog = buildUndoItem(beforeImage, afterImage);//将UndoLog设置到数据源连接代理ConnectionProxy中connectionProxy.appendUndoLog(sqlUndoLog);}}...
}

(2)构建全局锁的key的源码

public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {...//build lockKey//@param rowsIncludingPK the records//@return the string as local key. the local key example(multi pk): "t_user:1_a,2_b"protected String buildLockKey(TableRecords rowsIncludingPK) {if (rowsIncludingPK.size() == 0) {return null;}//构建出来的全局锁的key形式为：table_name:id_11001StringBuilder sb = new StringBuilder();sb.append(rowsIncludingPK.getTableMeta().getTableName());sb.append(":");int filedSequence = 0;//pksRows指的是，更新的每一行数据主键字段和主键的值List<Map<String, Field>> pksRows = rowsIncludingPK.pkRows();//获取到主键字段名称，主键可能是联合主键，主键字段的名称可能有多个List<String> primaryKeysOnlyName = getTableMeta().getPrimaryKeyOnlyName();//rowMap就是一行数据，rowMap中的key是字段名称，value是字段值for (Map<String, Field> rowMap : pksRows) {int pkSplitIndex = 0;//遍历和提取这行数据里多个主键字段的名称for (String pkName : primaryKeysOnlyName) {if (pkSplitIndex > 0) {sb.append("_");}//获取到多个主键字段的value，然后拼接在一起sb.append(rowMap.get(pkName).getValue());pkSplitIndex++;}filedSequence++;if (filedSequence < pksRows.size()) {sb.append(",");}}//最终拼成的key形如：table_name:1101_aadd,table_name:xxxx_xxxreturn sb.toString();}...
}

(3)构建UndoLog数据的源码

public abstract class BaseTransactionalExecutor<T, S extends Statement> implements Executor<T> {...//build a SQLUndoLog//@param beforeImage the before image//@param afterImage  the after imageprotected SQLUndoLog buildUndoItem(TableRecords beforeImage, TableRecords afterImage) {SQLType sqlType = sqlRecognizer.getSQLType();String tableName = sqlRecognizer.getTableName();SQLUndoLog sqlUndoLog = new SQLUndoLog();sqlUndoLog.setSqlType(sqlType);//SQL的类型可能为insert、update、deletesqlUndoLog.setTableName(tableName);//表的名称sqlUndoLog.setBeforeImage(beforeImage);//SQL执行前的数据镜像sqlUndoLog.setAfterImage(afterImage);//SQL执行后的数据镜像return sqlUndoLog;}...
}public class SQLUndoLog implements java.io.Serializable {private SQLType sqlType;private String tableName;private TableRecords beforeImage;private TableRecords afterImage;...
}

10.Seata Client发起分支事务注册的源码

(1)ConnectionProxy.commit()提交事务

(2)ConnectionProxy.register()注册分支事务

(1)ConnectionProxy.commit()提交事务

执行数据源连接代理ConnectionProxy的commit()方法提交事务的时候，首先会先调用数据源连接代理ConnectionProxy的register()方法注册分支事务。

public class ConnectionProxy extends AbstractConnectionProxy {private final ConnectionContext context = new ConnectionContext();...@Overridepublic void commit() throws SQLException {try {//通过全局锁重试策略组件来执行本地事务的提交lockRetryPolicy.execute(() -> {doCommit();return null;});} catch (SQLException e) {if (targetConnection != null && !getAutoCommit() && !getContext().isAutoCommitChanged()) {rollback();}throw e;} catch (Exception e) {throw new SQLException(e);}}private void doCommit() throws SQLException {if (context.inGlobalTransaction()) {processGlobalTransactionCommit();} else if (context.isGlobalLockRequire()) {processLocalCommitWithGlobalLocks();} else {targetConnection.commit();}}private void processLocalCommitWithGlobalLocks() throws SQLException {//检查全局锁keyscheckLock(context.buildLockKeys());try {//目标数据源连接提交事务targetConnection.commit();} catch (Throwable ex) {throw new SQLException(ex);}context.reset();}private void processGlobalTransactionCommit() throws SQLException {try {//注册分支事务register();} catch (TransactionException e) {recognizeLockKeyConflictException(e, context.buildLockKeys());}try {UndoLogManagerFactory.getUndoLogManager(this.getDbType()).flushUndoLogs(this);//目标数据源连接提交事务targetConnection.commit();} catch (Throwable ex) {LOGGER.error("process connectionProxy commit error: {}", ex.getMessage(), ex);report(false);throw new SQLException(ex);}if (IS_REPORT_SUCCESS_ENABLE) {report(true);}context.reset();}...
}

(2)ConnectionProxy.register()注册分支事务

执行数据源连接代理ConnectionProxy的register()方法注册分支事务的时候，会调用资源管理器DefaultResourceManager的branchRegister()方法，然后会继续调用AbstractResourceManager的branchRegister()方法来注册分支事务。

在AbstractResourceManager的branchRegister()方法中，首先会构造分支事务注册请求，然后通过RmNettyRemotingClient将分支事务注册请求发送给Seata Server。

//The type Connection proxy.
//数据源连接代理
public class ConnectionProxy extends AbstractConnectionProxy {private final ConnectionContext context = new ConnectionContext();...private void register() throws TransactionException {if (!context.hasUndoLog() || !context.hasLockKey()) {return;}//分支事务注册Long branchId = DefaultResourceManager.get().branchRegister(BranchType.AT,//事务类型getDataSourceProxy().getResourceId(),//资源id，资源是已经注册过了的null,context.getXid(),context.getApplicationData(),context.buildLockKeys()//注册分支事物时带上全局锁keys);context.setBranchId(branchId);}...
}public class DefaultResourceManager implements ResourceManager {protected static Map<BranchType, ResourceManager> resourceManagers = new ConcurrentHashMap<>();private static class SingletonHolder {private static DefaultResourceManager INSTANCE = new DefaultResourceManager();}public static DefaultResourceManager get() {return SingletonHolder.INSTANCE;}private DefaultResourceManager() {initResourceManagers();}protected void initResourceManagers() {//通过SPI加载所有的ResourceManager资源管理器//比如：DataSourceManager、TCCResourceManager、SagaResourceManager、ResourceManagerXAList<ResourceManager> allResourceManagers = EnhancedServiceLoader.loadAll(ResourceManager.class);if (CollectionUtils.isNotEmpty(allResourceManagers)) {for (ResourceManager rm : allResourceManagers) {resourceManagers.put(rm.getBranchType(), rm);}}}//注册分支事务@Overridepublic Long branchRegister(BranchType branchType, String resourceId, String clientId, String xid, String applicationData, String lockKeys) throws TransactionException {return getResourceManager(branchType).branchRegister(branchType, resourceId, clientId, xid, applicationData, lockKeys);}public ResourceManager getResourceManager(BranchType branchType) {ResourceManager rm = resourceManagers.get(branchType);if (rm == null) {throw new FrameworkException("No ResourceManager for BranchType:" + branchType.name());}return rm;}...
}public abstract class AbstractResourceManager implements ResourceManager {...@Overridepublic Long branchRegister(BranchType branchType, String resourceId, String clientId, String xid, String applicationData, String lockKeys) throws TransactionException {try {BranchRegisterRequest request = new BranchRegisterRequest();request.setXid(xid);//xid是全局事务idrequest.setLockKey(lockKeys);//这次分支事务要更新数据全局锁keyrequest.setResourceId(resourceId);//分支事务对应的资源idrequest.setBranchType(branchType);//分支事务类型request.setApplicationData(applicationData);//应用数据BranchRegisterResponse response = (BranchRegisterResponse) RmNettyRemotingClient.getInstance().sendSyncRequest(request);if (response.getResultCode() == ResultCode.Failed) {throw new RmTransactionException(response.getTransactionExceptionCode(), String.format("Response[ %s ]", response.getMsg()));}return response.getBranchId();} catch (TimeoutException toe) {throw new RmTransactionException(TransactionExceptionCode.IO, "RPC Timeout", toe);} catch (RuntimeException rex) {throw new RmTransactionException(TransactionExceptionCode.BranchRegisterFailed, "Runtime", rex);}}...
}