前言
在之前我们分析了，开启全局事务，和业务执行时是如何校验全局锁和提交本地事务的，接下来分析下是如何进行全局提交的。
二阶段全局提交
核心代码还是在TransactionalTemplate类中，当TC 没有收到异常时，就会进行全局提交逻辑：
提交和开启全局事务一样，也会在执行前后，添加钩子方法：
private void commitTransaction(GlobalTransaction tx) throws TransactionalExecutor.ExecutionException {
try {
triggerBeforeCommit();
tx.commit();
triggerAfterCommit();
} catch (TransactionException txe) {
// 4.1 Failed to commit
throw new TransactionalExecutor.ExecutionException(tx, txe,
TransactionalExecutor.Code.CommitFailure);
}
}
前置钩子执行完成后，进入到提交方法：
@Override
public void commit() throws TransactionException {
// 只有TC 才能进行全局提交
if (role == GlobalTransactionRole.Participant) {
// Participant has no responsibility of committing
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Ignore Commit(): just involved in global transaction [{}]", xid);
}
return;
}
// 检查XID
assertXIDNotNull();
// 重试次数，默认为5次
int retry = COMMIT_RETRY_COUNT <= 0 ? DEFAULT_TM_COMMIT_RETRY_COUNT : COMMIT_RETRY_COUNT;
try {
// 循环重试次数
while (retry > 0) {
try {
// 调用事务管理器，进行提交
status = transactionManager.commit(xid);
// 无异常退出循环
break;
} catch (Throwable ex) {
LOGGER.error("Failed to report global commit [{}],Retry Countdown: {}, reason: {}", this.getXid(), retry, ex.getMessage());
// 异常，进行重试
retry--;
if (retry == 0) {
throw new TransactionException("Failed to report global commit", ex);
}
}
}
} finally {
if (xid.equals(RootContext.getXID())) {
suspend();
}
}
if (LOGGER.isInfoEnabled()) {
LOGGER.info("[{}] commit status: {}", xid, status);
}
}
接着调用DefaultTransactionManager的提交方法，创建全局提交请求对象，设置xid，向TC 发起全局提交请求，并返回响应。
public GlobalStatus commit(String xid) throws TransactionException {
GlobalCommitRequest globalCommit = new GlobalCommitRequest();
globalCommit.setXid(xid);
GlobalCommitResponse response = (GlobalCommitResponse)this.syncCall(globalCommit);
return response.getGlobalStatus();
}
TC 接受全局提交请求
在TC端，处理请求的依然是DefaultCore类，它接受来自RM的rpc网络请求（branchRegister，branchReport，lockQuery）。同时DefaultCore继承TransactionManager接口，接受来自TM的rpc网络请求（begin，commit,rollback,getStatus）。
这里全局提交会进入到其commit 方法：
@Override
public GlobalStatus commit(String xid) throws TransactionException {
// 查询全局事务信息
GlobalSession globalSession = SessionHolder.findGlobalSession(xid);
// 没有全局事务信息，则会标记为已完成
if (globalSession == null) {
return GlobalStatus.Finished;
}
globalSession.addSessionLifecycleListener(SessionHolder.getRootSessionManager());
// 只需锁定状态即可
boolean shouldCommit = SessionHolder.lockAndExecute(globalSession, () -> {
// Highlight: Firstly, close the session, then no more branch can be registered.
// 关闭会话，然后不能再注册分支。
// 设置事务状态为未激活，
// 如果是AT 模式，还会释放全局锁，删除锁记录
globalSession.closeAndClean();
if (globalSession.getStatus() == GlobalStatus.Begin) {
if (globalSession.canBeCommittedAsync()) {
// 如果可以异步，则执行异步提交
globalSession.asyncCommit();
return false;
} else {
globalSession.changeStatus(GlobalStatus.Committing);
return true;
}
}
return false;
});
// 执行同步提交
if (shouldCommit) {
//
boolean success = doGlobalCommit(globalSession, false);
//If successful and all remaining branches can be committed asynchronously, do async commit.
if (success && globalSession.hasBranch() && globalSession.canBeCommittedAsync()) {
globalSession.asyncCommit();
return GlobalStatus.Committed;
} else {
return globalSession.getStatus();
}
} else {
// 异步提交时，直接返回已提交给TM 客户端Committed
return globalSession.getStatus() == GlobalStatus.AsyncCommitting ? GlobalStatus.Committed : globalSession.getStatus();
}
}
releaseGlobalSessionLock方法会进行全局锁的释放：
@Override
public boolean releaseGlobalSessionLock(GlobalSession globalSession) throws TransactionException {
// 获取当前事务的所有分支事务信息
List<BranchSession> branchSessions = globalSession.getBranchSessions();
if (CollectionUtils.isEmpty(branchSessions)) {
return true;
}
// 分支事务ID 集合
List<Long> branchIds = branchSessions.stream().map(BranchSession::getBranchId).collect(Collectors.toList());
try {
// 释放锁
return getLocker().releaseLock(globalSession.getXid(), branchIds);
} catch (Exception t) {
LOGGER.error("unLock globalSession error, xid:{} branchIds:{}", globalSession.getXid(),
CollectionUtils.toString(branchIds), t);
return false;
}
}
释放锁调用的是LockStoreDataBaseDAO.unLock，删除lock-table中改记录的全局锁。
@Override
public boolean unLock(String xid, List<Long> branchIds) {
Connection conn = null;
PreparedStatement ps = null;
try {
conn = lockStoreDataSource.getConnection();
conn.setAutoCommit(true);
StringJoiner sj = new StringJoiner(",");
branchIds.forEach(branchId -> sj.add("?"));
//batch release lock by branch list
// delete from lock_table where xid = ? and branch_id in (?,?)
String batchDeleteSQL = LockStoreSqlFactory.getLogStoreSql(dbType).getBatchDeleteLockSqlByBranchs(lockTable, sj.toString());
ps = conn.prepareStatement(batchDeleteSQL);
ps.setString(1, xid);
for (int i = 0; i < branchIds.size(); i++) {
ps.setLong(i + 2, branchIds.get(i));
}
ps.executeUpdate();
} catch (SQLException e) {
throw new StoreException(e);
} finally {
IOUtil.close(ps, conn);
}
return true;
}
异步提交
释放全局锁之后，进行异步提交，进入的是asyncCommit()方法，它只负责修改全局事务的状态，而具体的提交处理是交给TC 协调器来处理的。
public void asyncCommit() throws TransactionException {
// 添加监听器 DataBaseSessionManager
this.addSessionLifecycleListener(SessionHolder.getAsyncCommittingSessionManager());
// 修改数据库中 全局事务状态
SessionHolder.getAsyncCommittingSessionManager().addGlobalSession(this);
// 根据 AsyncCommitting 状态，数据库修改事务信息，状态为8（异步提交中）
this.changeStatus(GlobalStatus.AsyncCommitting);
}
TC 协调器
DefaultCoordinator是全球事务默认的事务控制协调器。它继承AbstractTCInboundHandler，可为TC接受到RM和TM的请求数据，并进行相应处理的处理器。实现TransactionMessageHandler接口，去处理收到的RPC信息，在顶级层面上，实现ResourceManagerInbound接口，发送至RM的branchCommit分支提交，branchRollback分支回滚请求。
在DefaultCoordinator类中定义了五个ScheduledThreadPoolExecutor（任务线程池执行器）属性：
//处理需要重试回滚的事务
private ScheduledThreadPoolExecutor retryRollbacking = new ScheduledThreadPoolExecutor(1,
new NamedThreadFactory("RetryRollbacking", 1));
//处理需要重试提交的事务
private ScheduledThreadPoolExecutor retryCommitting = new ScheduledThreadPoolExecutor(1,
new NamedThreadFactory("RetryCommitting", 1));
//处理需要异步提交的事务
private ScheduledThreadPoolExecutor asyncCommitting = new ScheduledThreadPoolExecutor(1,
new NamedThreadFactory("AsyncCommitting", 1));
//检测超时事务
private ScheduledThreadPoolExecutor timeoutCheck = new ScheduledThreadPoolExecutor(1,
new NamedThreadFactory("TxTimeoutCheck", 1));
//通知RM删除回滚日志
private ScheduledThreadPoolExecutor undoLogDelete = new ScheduledThreadPoolExecutor(1,
new NamedThreadFactory("UndoLogDelete", 1));
这五个定时线程池就是用于处理加入到事务管理器之后的事务。它们是在DefaultCoordinator的init方法中启动的：
public void init() {
//当通知分支事务回滚失败后，将全局事务加入到重试回滚管理器中，
//下面的线程池用于处理需要回滚的事务
retryRollbacking.scheduleAtFixedRate(() -> {
try {
handleRetryRollbacking();
} catch (Exception e) {
LOGGER.info("Exception retry rollbacking ... ", e);
}
}, 0, ROLLBACKING_RETRY_PERIOD, TimeUnit.MILLISECONDS);
//在AT模式下，下面的线程池不会使用
retryCommitting.scheduleAtFixedRate(() -> {
try {
handleRetryCommitting();
} catch (Exception e) {
LOGGER.info("Exception retry committing ... ", e);
}
}, 0, COMMITTING_RETRY_PERIOD, TimeUnit.MILLISECONDS);
//AT模式下全局事务提交都是异步提交，需要提交的全局事务都加入到异步提交管理器中，
//由下面的线程池处理
asyncCommitting.scheduleAtFixedRate(() -> {
try {
handleAsyncCommitting();
} catch (Exception e) {
LOGGER.info("Exception async committing ... ", e);
}
}, 0, ASYNC_COMMITTING_RETRY_PERIOD, TimeUnit.MILLISECONDS);
//遍历全局事务对象，查看是否有超时事务，如果事务超时了，
//则将全局事务对象加入到重试回滚管理器中，也就是下面交给retryRollbacking线程池处理
timeoutCheck.scheduleAtFixedRate(() -> {
try {
timeoutCheck();
} catch (Exception e) {
LOGGER.info("Exception timeout checking ... ", e);
}
}, 0, TIMEOUT_RETRY_PERIOD, TimeUnit.MILLISECONDS);
//通知RM删除若干天前的回滚日志，默认是7天，该线程池的线程定时每天运行一次
undoLogDelete.scheduleAtFixedRate(() -> {
try {
undoLogDelete();
} catch (Exception e) {
LOGGER.info("Exception undoLog deleting ... ", e);
}
}, UNDO_LOG_DELAY_DELETE_PERIOD, UNDO_LOG_DELETE_PERIOD, TimeUnit.MILLISECONDS);
}
除了undoLogDelete是每天运行一次之外，其他的都是每秒运行一次。
在上面全局异步提交中，当前事务的状态被修改了asyncCommitting提交中了，所以线程池asyncCommitting执行时，会获取到该全局事务并进行处理，进入的是handleAsyncCommitting方法：
/**
* Handle async committing.
*/
protected void handleAsyncCommitting() {
// 获取到 状态为提交中的所有事务信息
Collection<GlobalSession> asyncCommittingSessions = SessionHolder.getAsyncCommittingSessionManager()
.allSessions();
// 为空直接返回
if (CollectionUtils.isEmpty(asyncCommittingSessions)) {
return;
}
//asyncCommittingSession =》 GlobalSessionHandler内部类
SessionHelper.forEach(asyncCommittingSessions, asyncCommittingSession -> {
try {
// Instruction reordering in DefaultCore#asyncCommit may cause this situation
if (GlobalStatus.AsyncCommitting != asyncCommittingSession.getStatus()) {
//The function of this 'return' is 'continue'.
return;
}
asyncCommittingSession.addSessionLifecycleListener(SessionHolder.getRootSessionManager());
// 调用 DefaultCore 的doGlobalCommit
core.doGlobalCommit(asyncCommittingSession, true);
} catch (TransactionException ex) {
LOGGER.error("Failed to async committing [{}] {} {}", asyncCommittingSession.getXid(), ex.getCode(), ex.getMessage(), ex);
}
});
}
在DefaultCore 的doGlobalCommit中，完成全局事务提交：
@Override
public boolean doGlobalCommit(GlobalSession globalSession, boolean retrying) throws TransactionException {
boolean success = true;
// start committing event
// 发布事件
eventBus.post(new GlobalTransactionEvent(globalSession.getTransactionId(), GlobalTransactionEvent.ROLE_TC,
globalSession.getTransactionName(), globalSession.getApplicationId(), globalSession.getTransactionServiceGroup(),
globalSession.getBeginTime(), null, globalSession.getStatus()));
// 如果是SAGA 模式
if (globalSession.isSaga()) {
success = getCore(BranchType.SAGA).doGlobalCommit(globalSession, retrying);
} else {
// 遍历分支事务
Boolean result = SessionHelper.forEach(globalSession.getSortedBranches(), branchSession -> {
// if not retrying, skip the canBeCommittedAsync branches
// 不是重试中，毕竟能被异步提交，调到下一次循环
if (!retrying && branchSession.canBeCommittedAsync()) {
return CONTINUE;
}
BranchStatus currentStatus = branchSession.getStatus();
// 如果分支事务状态为 PhaseOne_Failed，则移除该分支并 调到下一次循环
if (currentStatus == BranchStatus.PhaseOne_Failed) {
globalSession.removeBranch(branchSession);
return CONTINUE;
}
try {
// 请求分支，提交分支事务
BranchStatus branchStatus = getCore(branchSession.getBranchType()).branchCommit(globalSession, branchSession);
// 判断分支事务的状态
switch (branchStatus) {
// 两阶段提交成功，移除分支事务信息
case PhaseTwo_Committed:
globalSession.removeBranch(branchSession);
return CONTINUE;
// 分支提交失败且不可重试
case PhaseTwo_CommitFailed_Unretryable:
// 全局事务是否能异步提交
// 可以，继续下一次循环
if (globalSession.canBeCommittedAsync()) {
LOGGER.error(
"Committing branch transaction[{}], status: PhaseTwo_CommitFailed_Unretryable, please check the business log.", branchSession.getBranchId());
return CONTINUE;
} else {
// 不可以，设置全局状态为 CommitFailed
SessionHelper.endCommitFailed(globalSession);
LOGGER.error("Committing global transaction[{}] finally failed, caused by branch transaction[{}] commit failed.", globalSession.getXid(), branchSession.getBranchId());
return false;
}
default:
// 没有成功，也没有不可重试，说明是可重试的
if (!retrying) {
globalSession.queueToRetryCommit();
return false;
}
if (globalSession.canBeCommittedAsync()) {
LOGGER.error("Committing branch transaction[{}], status:{} and will retry later",
branchSession.getBranchId(), branchStatus);
return CONTINUE;
} else {
LOGGER.error(
"Committing global transaction[{}] failed, caused by branch transaction[{}] commit failed, will retry later.", globalSession.getXid(), branchSession.getBranchId());
return false;
}
}
} catch (Exception ex) {
StackTraceLogger.error(LOGGER, ex, "Committing branch transaction exception: {}",
new String[] {
branchSession.toString()});
if (!retrying) {
globalSession.queueToRetryCommit();
throw new TransactionException(ex);
}
}
return CONTINUE;
});
// Return if the result is not null
if (result != null) {
return result;
}
//如果有分支，并且不是所有剩余的分支都可以异步提交，打印日志并返回false
if (globalSession.hasBranch() && !globalSession.canBeCommittedAsync()) {
LOGGER.info("Committing global transaction is NOT done, xid = {}.", globalSession.getXid());
return false;
}
}
// 如果成功且没有分支事务，则结束全局事务
if (success && globalSession.getBranchSessions().isEmpty()) {
SessionHelper.endCommitted(globalSession);
// 发布提交成功通知
eventBus.post(new GlobalTransactionEvent(globalSession.getTransactionId(), GlobalTransactionEvent.ROLE_TC,
globalSession.getTransactionName(), globalSession.getApplicationId(), globalSession.getTransactionServiceGroup(),
globalSession.getBeginTime(), System.currentTimeMillis(), globalSession.getStatus()));
LOGGER.info("Committing global transaction is successfully done, xid = {}.", globalSession.getXid());
}
// 返回成功
return success;
}
分支处理提交请求
在上面的TC 进行doGlobalCommit 方法处理提交时，会循环调用每一个分支，向分支发送提交请求。
Netty 客户端收到请求后，RM 会调用处理器DefaultRMHandler处理分支提交
protected void doBranchCommit(BranchCommitRequest request, BranchCommitResponse response) throws TransactionException {
// 提交事务信息
String xid = request.getXid();
long branchId = request.getBranchId();
String resourceId = request.getResourceId();
String applicationData = request.getApplicationData();
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Branch committing: " + xid + " " + branchId + " " + resourceId + " " + applicationData);
}
// 调用RM 进行提交
BranchStatus status = this.getResourceManager().branchCommit(request.getBranchType(), xid, branchId, resourceId, applicationData);
// 返回给TC 提交结果
response.setXid(xid);
response.setBranchId(branchId);
response.setBranchStatus(status);
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Branch commit result: " + status);
}
}
RM会调用一个异步处理类AsyncWorker进行处理 ，会添加到异步队列，然后直接返回成功给TC 。
public BranchStatus branchCommit(String xid, long branchId, String resourceId) {
// 获取上下文
AsyncWorker.Phase2Context context = new AsyncWorker.Phase2Context(xid, branchId, resourceId);
// 添加到提交队列中
this.addToCommitQueue(context);
// 返回提交成功
return BranchStatus.PhaseTwo_Committed;
}
// 添加到异步队列
private void addToCommitQueue(AsyncWorker.Phase2Context context) {
if (!this.commitQueue.offer(context)) {
CompletableFuture.runAsync(this::doBranchCommitSafely, this.scheduledExecutor).thenRun(() -> {
this.addToCommitQueue(context);
});
}
}
在异步队列中，AsyncWorker会批量地删除相应 UNDO LOG 记录，至此，分支事务提交就全部完成了。
private void dealWithGroupedContexts(String resourceId, List<AsyncWorker.Phase2Context> contexts) {
DataSourceProxy dataSourceProxy = this.dataSourceManager.get(resourceId);
if (dataSourceProxy == null) {
LOGGER.warn("Failed to find resource for {}", resourceId);
} else {
Connection conn;
try {
conn = dataSourceProxy.getPlainConnection();
} catch (SQLException var7) {
LOGGER.error("Failed to get connection for async committing on {}", resourceId, var7);
return;
}
UndoLogManager undoLogManager = UndoLogManagerFactory.getUndoLogManager(dataSourceProxy.getDbType());
List<List<AsyncWorker.Phase2Context>> splitByLimit = Lists.partition(contexts, 1000);
// 批量删除
splitByLimit.forEach((partition) -> {
this.deleteUndoLog(conn, undoLogManager, partition);
});
}
}