关于mysql:源码分析-MySQL-的-commit-是怎么-commit-的

作者：李鹏博
爱可生 DBA 团队成员，次要负责 MySQL 故障解决和 SQL 审核优化。对技术执着，为客户负责。
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MySQL 的 commit 命令提交事务时，外部会进行两阶段（Prepare 和 Commit）提交，这篇文章基于 MySQL 8.0.33 对 MySQL 的两阶段提交进行源码剖析，带你理解提交事务过程中都经验了什么。

获取上一个事务最大的 sequence number 工夫戳。

事务状态设置为 prepared；
开释 RC 及以下隔离级别的 GAP Lock；
将 Undo log segment 的状态从 TRX_UNDO_ACTIVE 批改为 TRX_UNDO_PREPARED；
Undo log 写入事务 XID。

保障从实例的 commit order。

依据 innodb_flush_log_at_trx_commit 参数进行 redo log 的刷盘操作
- 获取并清空 BINLOG_FLUSH_STAGE 和 COMMIT_ORDER_FLUSH_STAGE 队列
- 存储引擎层将 prepare 状态的 redo log 依据 innodb_flush_log_at_trx_commit 参数刷盘
- 不再阻塞 slave 的 preserve commit order 的执行
调用 get_server_sidno() 和 Gtid_state::get_automatic_gno() 生成 GTID
Flush binlog_cache_mngr
- Flush stmt_cache
- Flush trx_cache
  - 生成 last_committed 和 sequence_number
  - flush GTID log event
  - 将 trx_cache 中的数据 flush 到 binlog cache 中
  - 筹备提交事务后的 Binlog pos
  - 递增 prepread XID
插桩调用 after_flush，将曾经 flush 的 binlog file 和 position 注册到半同步复制插件中
如果 sync_binlog!=1，在 flush stage 更新 Binlog 位点，并播送 update 信号，从库的 Dump 线程能够由此感知 Binlog 的更新

依据 sync_binlog 的参数设置进行刷盘前的期待并调用 fsync() 进行刷盘
如果 sync_binlog==1，在 sync stage 阶段更新 binog 位点，并播送 update 信号，从库的 Dump 线程能够由此感知 Binlog 的更新

after_sync hook（半同步复制 after_sync 的钩子）
更新全局的 m_max_committed_transaction（用作后续事务的 last_committed），并初始化事务上下文的 sequence number
Binlog 层提交，什么也不做

存储引擎层提交

为长久化 GTID 提前调配 update undo segment
更新数据字典中被批改表的 update_time 工夫
调配 Mini-transaction handle 和 buffer

更新 undo 状态

   - 对于 insert 状态从 TRX_UNDO_ACTIVE 批改为 TRX_UNDO_TO_FREE，update 批改为 TRX_UNDO_TO_PURGE
  - 如果事务为 update 还须要将 rollback segments 调配 trx no，并将其增加到 purge 队列中

将 update undo log header 增加到 history list 结尾开释一些内存对象
在零碎事务表记录 binlog 位点
敞开 mvcc read view
长久化 GTID
开释 insert undo log
唤醒后盾线程开始干活，如 master thread、purge thread、page_cleaner

更新整组事务的 executed_gtid
在存储引擎层提交之后，递加 Prepared 状态下的 XID 计数器
after_sync hook（半同步复制 after_commit 的钩子）
播送 m_stage_cond_binlog 信号变量，唤醒挂起的 follower

ha_commit_trans 函数次要判断是否须要写入 GTID 信息，并开始两阶段提交：

 int ha_commit_trans(THD *thd, bool all, bool ignore_global_read_lock) {
  /*
    Save transaction owned gtid into table before transaction prepare
    if binlog is disabled, or binlog is enabled and log_replica_updates
    is disabled with slave SQL thread or slave worker thread.
  */
  std::tie(error, need_clear_owned_gtid) = commit_owned_gtids(thd, all);
...
  // Prepare 阶段
  if (!trn_ctx->no_2pc(trx_scope) && (trn_ctx->rw_ha_count(trx_scope) > 1))
    error = tc_log->prepare(thd, all);
...
  // Commit 阶段
 if (error || (error = tc_log->commit(thd, all))) {ha_rollback_trans(thd, all);
    error = 1;
    goto end;
  }
}

两阶段提交的 Prepare 阶段绝对简略，以下是 commit 命令入口及 Prepare 阶段的堆栈和相干作用：

 |mysql_execute_command
|--trans_commit
|----ha_commit_trans
|------MYSQL_BIN_LOG::prepare
 
// 开启 binlog prepare 和 innodb prepare
|--------ha_prepare_low       
 
// Binlog prepare：获取上一个事务最大的 sequence number 工夫戳
|----------binlog_prepare   
 
// innodb prepare
|----------innobase_xa_prepare                
|------------trx_prepare_for_mysql
 
// 1. 调用 trx_prepare_low 
// 2. 事务状态设置为 Prepared 
// 3. 开释 RC 及以下隔离级别的 GAP Lock 
// 4. 刷盘 Redo（已推延到 Commit 阶段的 Flush stage）|--------------trx_prepare                        
|----------------trx_prepare_low
 
// 1. 将 undo log segment 的状态从 TRX_UNDO_ACTIVE 批改为 TRX_UNDO_PREPARED 
// 2. undo log 写入事务 XID
|------------------trx_undo_set_state_at_prepare

Commit 阶段的性能实现次要集中在 MYSQL_BIN_LOG::ordered_commit 函数中。

首先看下 Stage 0 和 Stage 1，stage 0 次要是 8.0 新增的一个阶段，次要是针对从库保障 commit order。stage 1 就是大家耳熟能详的 Commit 阶段的三个小阶段其一的 Flush 阶段了：

 int MYSQL_BIN_LOG::ordered_commit(THD *thd, bool all, bool skip_commit) {
 
  /*
    Stage #0: 保障从实例的 SQL 线程依照 Relay log 的事务程序进行提交
  */
  if (Commit_order_manager::wait_for_its_turn_before_flush_stage(thd) ||
      ending_trans(thd, all) ||
      Commit_order_manager::get_rollback_status(thd)) {if (Commit_order_manager::wait(thd)) {return thd->commit_error;}
  }
 
  /*
    Stage #1: flushing transactions to binary log
 
    While flushing, we allow new threads to enter and will process
    them in due time. Once the queue was empty, we cannot reap
    anything more since it is possible that a thread entered and
    appointed itself leader for the flush phase.
  */
 
  if (change_stage(thd, Commit_stage_manager::BINLOG_FLUSH_STAGE, thd, nullptr,
                   &LOCK_log)) {DBUG_PRINT("return", ("Thread ID: %u, commit_error: %d", thd->thread_id(),
                          thd->commit_error));
    return finish_commit(thd);
  }
 
  THD *wait_queue = nullptr, *final_queue = nullptr;
  mysql_mutex_t *leave_mutex_before_commit_stage = nullptr;
  my_off_t flush_end_pos = 0;
  bool update_binlog_end_pos_after_sync;
 
  // Flush 阶段次要的解决逻辑
  flush_error =
      process_flush_stage_queue(&total_bytes, &do_rotate, &wait_queue);
 
  if (flush_error == 0 && total_bytes > 0)
    /*
      flush binlog cache 到 file cache
    */
    flush_error = flush_cache_to_file(&flush_end_pos);
 
  // 前面依据 sync_binlog 参数决定更新 binlog pos 的地位并播送 Binlog 更新信号
  update_binlog_end_pos_after_sync = (get_sync_period() == 1);
 
  /*
    If the flush finished successfully, we can call the after_flush
    hook. Being invoked here, we have the guarantee that the hook is
    executed before the before/after_send_hooks on the dump thread
    preventing race conditions among these plug-ins.
  */
  if (flush_error == 0) {const char *file_name_ptr = log_file_name + dirname_length(log_file_name);
    assert(flush_end_pos != 0);
    /*
      插桩调用 after_flush，将曾经 flush 的 binlog file 和 position 注册到半同步复制插件中，用于后续比照 slave 应答承受到的 binlog position。*/
    if (RUN_HOOK(binlog_storage, after_flush,
                 (thd, file_name_ptr, flush_end_pos))) {LogErr(ERROR_LEVEL, ER_BINLOG_FAILED_TO_RUN_AFTER_FLUSH_HOOK);
      flush_error = ER_ERROR_ON_WRITE;
    }
 
    // 如果 sync_binlog!=1，在 flush stage 更新 binlog 位点并播送 update 信号，从库的 Dump 线程能够由此感知 Binlog 的更新
    if (!update_binlog_end_pos_after_sync) update_binlog_end_pos();}

Flush stage 的次要解决逻辑集中在 process_flush_stage_queue：

  
int MYSQL_BIN_LOG::process_flush_stage_queue(my_off_t *total_bytes_var,
                                             bool *rotate_var,
                                             THD **out_queue_var) {
 
  int no_flushes = 0;
  my_off_t total_bytes = 0;
  mysql_mutex_assert_owner(&LOCK_log);
  // 依据 innodb_flush_log_at_trx_commit 参数进行 redo log 的刷盘操作
  THD *first_seen = fetch_and_process_flush_stage_queue();
 
  // 调用 get_server_sidno() 和 Gtid_state::get_automatic_gno 生成 GTID
  assign_automatic_gtids_to_flush_group(first_seen);
  /* Flush thread caches to binary log. */
  for (THD *head = first_seen; head; head = head->next_to_commit) {Thd_backup_and_restore switch_thd(current_thd, head);
    /*
      flush binlog_cache_mngr 的 stmt_cache 和 trx_cache。flush trx_cache：- 生成 last_committed 和 sequence_number
        - flush GTID log event
        - 将 trx_cache 中的数据 flush 到 binlog cache 中
        - 筹备提交事务后的 Binlog pos
        - 递增 prepread XID
    */
    std::pair<int, my_off_t> result = flush_thread_caches(head);
    total_bytes += result.second;
    if (flush_error == 1) flush_error = result.first;
#ifndef NDEBUG
    no_flushes++;
#endif
  }
 
  *out_queue_var = first_seen;
  *total_bytes_var = total_bytes;
  if (total_bytes > 0 &&
      (m_binlog_file->get_real_file_size() >= (my_off_t)max_size ||
       DBUG_EVALUATE_IF("simulate_max_binlog_size", true, false)))
    *rotate_var = true;
#ifndef NDEBUG
  DBUG_PRINT("info", ("no_flushes:= %d", no_flushes));
  no_flushes = 0;
#endif
  return flush_error;
}

redo log 刷盘的堆栈如下：

  
// 获取并清空 BINLOG_FLUSH_STAGE 和 COMMIT_ORDER_FLUSH_STAGE 队列，flush 事务到磁盘；不再阻塞 slave 的 preserve commit order 的执行
|fetch_and_process_flush_stage_queue  
 
// 存储引擎层将 prepare 状态的 redo log 依据 innodb_flush_log_at_trx_commit 参数刷盘
|--ha_flush_logs                      
|----innobase_flush_logs
|------log_buffer_flush_to_disk

Sync 阶段的代码如下：

 /*
  Stage #2: Syncing binary log file to disk
*/
 
if (change_stage(thd, Commit_stage_manager::SYNC_STAGE, wait_queue, &LOCK_log,
                 &LOCK_sync)) {DBUG_PRINT("return", ("Thread ID: %u, commit_error: %d", thd->thread_id(),
                        thd->commit_error));
  return finish_commit(thd);
}
 
/*
  - sync_counter：commit group 的数量
  - get_sync_period()：获取 sync_binlog 参数的值
  - 如果 sync stage 队列中的 commit group 大于等于 sync_binlog 的值，以后 leader 就调用 fsync()进行刷盘操作（sync_binlog_file(false)），在 sync 之前可能会进行期待，期待更多的 commit group 入队，期待的工夫为 binlog_group_commit_sync_no_delay_count 或 binlog_group_commit_sync_delay，默认都为 0。- 如果 sync stage 队列中的 commit group 小于 sync_binlog 的值，以后 leader 不会调用 fsync()进行刷盘也不会期待
  - 如果 sync_binlog 为 0，每个 commit group 都会触发期待动作，然而不会 sync
  - 如果 sync_binlog 为 1，每个 commit group 都会触发期待动作，且会 sync
*/
if (!flush_error && (sync_counter + 1 >= get_sync_period()))
  Commit_stage_manager::get_instance().wait_count_or_timeout(
      opt_binlog_group_commit_sync_no_delay_count,
      opt_binlog_group_commit_sync_delay, Commit_stage_manager::SYNC_STAGE);
 
final_queue = Commit_stage_manager::get_instance().fetch_queue_acquire_lock(Commit_stage_manager::SYNC_STAGE);
 
if (flush_error == 0 && total_bytes > 0) {DEBUG_SYNC(thd, "before_sync_binlog_file");
  std::pair<bool, bool> result = sync_binlog_file(false);
  sync_error = result.first;
}
 
/*
 如果 sync_binlog==1, 在 sync stage 阶段更新 binog 位点，并播送 update 信号，从库的 Dump 线程能够由此感知 Binlog 的更新（位点在 flush stage 中的 process_flush_stage_queue()
                       |--flush_thread_caches()
                       |-----set_trans_pos()函数中设置）*/
if (update_binlog_end_pos_after_sync && flush_error == 0 && sync_error == 0) {
  THD *tmp_thd = final_queue;
  const char *binlog_file = nullptr;
  my_off_t pos = 0;
 
  while (tmp_thd != nullptr) {if (tmp_thd->commit_error == THD::CE_NONE) {tmp_thd->get_trans_fixed_pos(&binlog_file, &pos);
    }
    tmp_thd = tmp_thd->next_to_commit;
  }
 
  if (binlog_file != nullptr && pos > 0) {update_binlog_end_pos(binlog_file, pos);
  }
}
 
DEBUG_SYNC(thd, "bgc_after_sync_stage_before_commit_stage");
 
leave_mutex_before_commit_stage = &LOCK_sync;

Commit 阶段的代码如下：

   /*
    Stage #3: Commit all transactions in order.
  */
commit_stage:
  /* binlog_order_commits：是否进行 order commit，即放弃 redo 和 binlog 的提交程序统一 */
  if ((opt_binlog_order_commits || Clone_handler::need_commit_order()) &&
      (sync_error == 0 || binlog_error_action != ABORT_SERVER)) {
    if (change_stage(thd, Commit_stage_manager::COMMIT_STAGE, final_queue,
                     leave_mutex_before_commit_stage, &LOCK_commit)) {DBUG_PRINT("return", ("Thread ID: %u, commit_error: %d", thd->thread_id(),
                            thd->commit_error));
      return finish_commit(thd);
    }
    THD *commit_queue =
        Commit_stage_manager::get_instance().fetch_queue_acquire_lock(Commit_stage_manager::COMMIT_STAGE);
    DBUG_EXECUTE_IF("semi_sync_3-way_deadlock",
                    DEBUG_SYNC(thd, "before_process_commit_stage_queue"););
 
    if (flush_error == 0 && sync_error == 0)
      /* after_sync hook */
      sync_error = call_after_sync_hook(commit_queue);
 
    /*
      Commit 阶段的次要解决逻辑
    */
    process_commit_stage_queue(thd, commit_queue);
 
    /**
     * After commit stage
     */
    if (change_stage(thd, Commit_stage_manager::AFTER_COMMIT_STAGE,
                     commit_queue, &LOCK_commit, &LOCK_after_commit)) {DBUG_PRINT("return", ("Thread ID: %u, commit_error: %d", thd->thread_id(),
                            thd->commit_error));
      return finish_commit(thd);
    }
 
    THD *after_commit_queue =
        Commit_stage_manager::get_instance().fetch_queue_acquire_lock(Commit_stage_manager::AFTER_COMMIT_STAGE);
    /* after_commit hook */
    process_after_commit_stage_queue(thd, after_commit_queue);
 
    final_queue = after_commit_queue;
    mysql_mutex_unlock(&LOCK_after_commit);
  } else {if (leave_mutex_before_commit_stage)
      mysql_mutex_unlock(leave_mutex_before_commit_stage);
    if (flush_error == 0 && sync_error == 0)
      sync_error = call_after_sync_hook(final_queue);
  }
 
 
  /* 播送 m_stage_cond_binlog 信号变量，唤醒挂起的 follower */
  Commit_stage_manager::get_instance().signal_done(final_queue);
  DBUG_EXECUTE_IF("block_leader_after_delete", {const char action[] = "now SIGNAL leader_proceed";
    assert(!debug_sync_set_action(thd, STRING_WITH_LEN(action)));
  };);
 
  /*
    Finish the commit before executing a rotate, or run the risk of a
    deadlock. We don't need the return value here since it is in
    thd->commit_error, which is returned below.
  */
  (void)finish_commit(thd);
  DEBUG_SYNC(thd, "bgc_after_commit_stage_before_rotation");
 
  return thd->commit_error == THD::CE_COMMIT_ERROR;
}

Commit 阶段的次要解决逻辑集中在 process_commit_stage_queue 函数中：

 void MYSQL_BIN_LOG::process_commit_stage_queue(THD *thd, THD *first) {mysql_mutex_assert_owner(&LOCK_commit);
#ifndef NDEBUG
  thd->get_transaction()->m_flags.ready_preempt =
      true;  // formality by the leader
#endif
  for (THD *head = first; head; head = head->next_to_commit) {
    DBUG_PRINT("debug", ("Thread ID: %u, commit_error: %d, commit_pending: %s",
                         head->thread_id(), head->commit_error,
                         YESNO(head->tx_commit_pending)));
    DBUG_EXECUTE_IF(
        "block_leader_after_delete",
        if (thd != head) {DBUG_SET("+d,after_delete_wait"); };);
    /*
      If flushing failed, set commit_error for the session, skip the
      transaction and proceed with the next transaction instead. This
      will mark all threads as failed, since the flush failed.
 
      If flush succeeded, attach to the session and commit it in the
      engines.
    */
#ifndef NDEBUG
    Commit_stage_manager::get_instance().clear_preempt_status(head);
#endif
    /*
      更新全局的 m_max_committed_transaction（用作后续事务的 last_committed），并初始本事务上下文的 sequence number
    */
    if (head->get_transaction()->sequence_number != SEQ_UNINIT) {mysql_mutex_lock(&LOCK_replica_trans_dep_tracker);
      m_dependency_tracker.update_max_committed(head);
      mysql_mutex_unlock(&LOCK_replica_trans_dep_tracker);
    }
    /*
      Flush/Sync error should be ignored and continue
      to commit phase. And thd->commit_error cannot be
      COMMIT_ERROR at this moment.
    */
    assert(head->commit_error != THD::CE_COMMIT_ERROR);
    Thd_backup_and_restore switch_thd(thd, head);
    bool all = head->get_transaction()->m_flags.real_commit;
    assert(!head->get_transaction()->m_flags.commit_low ||
           head->get_transaction()->m_flags.ready_preempt);<br>  // Binlog Commit、Innodb Commit
    ::finish_transaction_in_engines(head, all, false);
    DBUG_PRINT("debug", ("commit_error: %d, commit_pending: %s",
                         head->commit_error, YESNO(head->tx_commit_pending)));
  }
 
  /*
    锁定 sidno，更新整组事务 的 executed_gtid
    - 如果没开启 binlog，@@GLOBAL.GTID_PURGED 的值是从 executed_gtid 获取的，此时 @@GLOBAL.GTID_PURGED 的值和 @@GLOBAL.GTID_EXECUTED 永远是统一的，就不须要在记录 lost_gtids
    - 如果开启了 binlog，然而未开启 log_replica_updates，slave 的 SQL 线程或 slave worker 线程
      将本身的 GTID 更新到 executed_gtids、lost_gtids
  */
  gtid_state->update_commit_group(first);
 
  for (THD *head = first; head; head = head->next_to_commit) {Thd_backup_and_restore switch_thd(thd, head);
    auto all = head->get_transaction()->m_flags.real_commit;
    // 只针对内部 XA 事务，在存储引擎层将事务标记为 Prepared
    trx_coordinator::set_prepared_in_tc_in_engines(head, all);
    /*
      在存储引擎层提交之后，递加 Prepared 状态下的 XID 计数器
    */
    if (head->get_transaction()->m_flags.xid_written) dec_prep_xids(head);
  }
}

其中::finish_transaction_in_engines 函数是次要的存储引擎层提交逻辑，相干堆栈如下：

 |::finish_transaction_in_engines
|--trx_coordinator::commit_in_engines
|----ha_commit_low
 
// Binlog 层提交什么也不做（空函数）|------binlog_commit
 
// 存储引擎层提交
|------innobase_commit                                
|--------innobase_commit_low
|----------trx_commit_for_mysql
 
// 为长久化 GTID 提前调配 update undo segment
|------------trx_undo_gtid_add_update_undo  
 
// 更新数据字典中被批改表的 update_time 工夫
|------------trx_update_mod_tables_timestamp     
 
// 调配 Mini-transaction handle 和 buffer
|------------trx_commit          
 
// 提交 mini-transaction
|--------------trx_commit_low                         
|----------------trx_write_serialisation_history
 
// 更新 undo 状态：// 对于 insert 状态从 TRX_UNDO_ACTIVE 批改为 TRX_UNDO_TO_FREE
// update 批改为 TRX_UNDO_TO_PURGE
// 如果事务为 update 还须要将 rollback segments 调配 trx no，并将其增加到 purge 队列中
|------------------trx_undo_set_state_at_finish      
 
// 将 update undo log header 增加到 history list 结尾开释一些内存对象;
|------------------trx_undo_update_cleanup  
 
 // 在零碎事务表记录 binlog 位点
|------------------trx_sys_update_mysql_binlog_offset 
|----------------trx_commit_in_memory
 
//- 敞开 mvcc read view
//- 长久化 GTID
//- 开释 insert undo log
//- 唤醒后盾线程开始干活，如：master thread、purge thread、page_cleaner

阶段转换的逻辑次要是由 change_stage 中的 enroll_for 函数实现：

进入队列的第一个线程会作为整组事务的 leader
后续进入队列的线程会作为整组事务的 follower
follower 线程挂起期待 m_stage_cond_binlog 信号变量唤醒
leader 负责提交整组事务，提交实现后，发送 m_stage_cond_binlog 信号变量唤醒挂起的 follower
队列转化的次要逻辑是线程先入下个阶段的队列，而后再开释上一个阶段的 mutex，而后再获取下一个阶段的 mutex
Flush Stage 不会获取 mutex
Sync Stage 须要获取 LOCK_sync
Commit Stage 须要获取 LOCK_commit mutex
After Commit Stage 须要获取 LOCK_after_commit mutex

 bool Commit_stage_manager::enroll_for(StageID stage, THD *thd,
                                     mysql_mutex_t *stage_mutex,
                                     mysql_mutex_t *enter_mutex) {
 // 如果队列为空，线程就是 leader
 thd->rpl_thd_ctx.binlog_group_commit_ctx().assign_ticket();
 bool leader = this->append_to(stage, thd);
 
 /*
  如果 FLUSH stage 队列（(BINLOG_FLUSH_STAGE 或 COMMIT_ORDER_FLUSH_STAGE）不为空，此线程就不能成为 leader。leader
  须要获取 enter_mutex
 */
 if (leader) {if (stage == COMMIT_ORDER_FLUSH_STAGE) {leader = m_queue[BINLOG_FLUSH_STAGE].is_empty();
   /*
     leader 转换的逻辑。session 的队列有 5 种：- Binlog flush queue: flush redo 并写 Binlog File
       - Commit order flush queue: 针对 commit order 的事务，然而会参加 group commit 的结尾局部，直到引擎层的 flush。- Sync queue: sync transaction
       - Commit queue: 提交事务
       - After commit queue: 调用事务的 after_commit hook
    */
   } else if (stage == BINLOG_FLUSH_STAGE &&  // 以后线程是 BINLOG_FLUSH_STAGE 中的第一个线程；然而 COMMIT_ORDER_FLUSH_STAGE
                                              // 曾经有了 leader，此时以后线程会挂起，期待 COMMIT_ORDER_FLUSH_STAGE 的 leader 的信号唤醒
              !m_queue[COMMIT_ORDER_FLUSH_STAGE].is_empty()) {
     /*
       以后事务是 binlog queue 中的第一个线程，然而在 commit order queue 中曾经有了一个 leader。此时以后线程会作为 leader，而 commit order leader 会转变为 follower。扭转 leader 的起因是 commit order leader 不能作为 binlog 线程的 leader，因为 commit order threads
       必须在 binlog threads 操作完之前来到 commit group。转变 leader 为 followers 的步骤如下：1. commit order thread 首先进入 flush stage，并成为 commit order leader。2. commit order leader 尝试获取 stage mutex，这可能会须要一些工夫，比方 mutex 曾经被上一个
       commit group 的 leader 获取。3. 在此期间，一个 binlog 线程进入了 flush stage。它须要期待来自 commit order leader 的信号。4. commit order leader 获取了 stage mutex，而后它会查看是否有  binlog thread 进入了 flush stage，如果发现了就转变 leader。5. commit order leader 给  binlog leader 发送一个信号，并成为 follower，期待 commit 的实现（和其余 follower 的行为统一）。6. binlog leader 被 commit order leader 的信号唤醒并执行 group commit。*/
     CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("before_binlog_leader_wait");
     while (thd->tx_commit_pending)
       mysql_cond_wait(&m_stage_cond_leader,
                       &m_queue_lock[BINLOG_FLUSH_STAGE]);
   }
 }
 
 unlock_queue(stage);
 
 /*
   告诉下一个组提交事务进入队列
 */
 if (stage == BINLOG_FLUSH_STAGE) {Commit_order_manager::finish_one(thd);
   CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("after_binlog_leader_wait");
 } else if (stage == COMMIT_ORDER_FLUSH_STAGE) {Commit_order_manager::finish_one(thd);
 }
 
 /*
   当进入第一个 stage 时，能够不必获取 stage mutex
 */
 if (stage_mutex && need_unlock_stage_mutex) mysql_mutex_unlock(stage_mutex);
 
 /*
   如果队列非空，以后线程作为 follower 期待 leader 解决队列
 */
 if (!leader) {CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("before_follower_wait");
   mysql_mutex_lock(&m_lock_done);
#ifndef NDEBUG
   thd->get_transaction()->m_flags.ready_preempt = true;
   if (leader_await_preempt_status) mysql_cond_signal(&m_cond_preempt);
#endif
   // tx_commit_pending：还有事务 commit 操作未实现
   while (thd->tx_commit_pending) {if (stage == COMMIT_ORDER_FLUSH_STAGE) {mysql_cond_wait(&m_stage_cond_commit_order, &m_lock_done);
     } else {
       // follower 线程在此处挂起，期待 leader 提交事务实现后被唤醒
       mysql_cond_wait(&m_stage_cond_binlog, &m_lock_done);
     }
   }
 
   mysql_mutex_unlock(&m_lock_done);
   return false;
 }
 
#ifndef NDEBUG
 if (stage == Commit_stage_manager::SYNC_STAGE)
   DEBUG_SYNC(thd, "bgc_between_flush_and_sync");
#endif
 
 bool need_lock_enter_mutex = false;
 if (leader && enter_mutex != nullptr) {
   /*
     如果因为在轮替 Binlog 时曾经获取了 LOCK_log，就不在须要获取 enter_mutex。*/
   need_lock_enter_mutex = !(mysql_bin_log.is_rotating_caused_by_incident &&
                             enter_mutex == mysql_bin_log.get_log_lock());
 
   if (need_lock_enter_mutex)
     mysql_mutex_lock(enter_mutex);
   else
     mysql_mutex_assert_owner(enter_mutex);
 }
 
 // leader 转换的逻辑
 if (stage == COMMIT_ORDER_FLUSH_STAGE) {
   CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("after_commit_order_thread_becomes_leader");
   lock_queue(stage);
 
   if (!m_queue[BINLOG_FLUSH_STAGE].is_empty()) {if (need_lock_enter_mutex) mysql_mutex_unlock(enter_mutex);
 
     THD *binlog_leader = m_queue[BINLOG_FLUSH_STAGE].get_leader();
     binlog_leader->tx_commit_pending = false;
 
     mysql_cond_signal(&m_stage_cond_leader);
     unlock_queue(stage);
 
     mysql_mutex_lock(&m_lock_done);
     /* wait for signal from binlog leader */
     CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("before_commit_order_leader_waits_for_binlog_leader");
     while (thd->tx_commit_pending)
       mysql_cond_wait(&m_stage_cond_commit_order, &m_lock_done);
     mysql_mutex_unlock(&m_lock_done);
 
     leader = false;
     return leader;
   }
 }
 
 return leader;
}

关于mysql:源码分析-MySQL-的-commit-是怎么-commit-的

一、Prepare 阶段

1. Binlog Prepare

2. InnoDB Prepare

二、Commit 阶段

1. Stage 0

2. Flush Stage

3. Sync Stage

4. Commit Stage

Prepare 阶段

Commit 阶段

Flush 阶段

SYNC 阶段

COMMIT 阶段

阶段转换

Just My Socks（注册教程内含优惠码）

	- 对于 insert 状态从 TRX_UNDO_ACTIVE 批改为 TRX_UNDO_TO_FREE，update 批改为 TRX_UNDO_TO_PURGE
	- 如果事务为 update 还须要将 rollback segments 调配 trx no，并将其增加到 purge 队列中

	int ha_commit_trans(THD *thd, bool all, bool ignore_global_read_lock) {
	/*
	Save transaction owned gtid into table before transaction prepare
	if binlog is disabled, or binlog is enabled and log_replica_updates
	is disabled with slave SQL thread or slave worker thread.
	*/
	std::tie(error, need_clear_owned_gtid) = commit_owned_gtids(thd, all);
	...
	// Prepare 阶段
	if (!trn_ctx->no_2pc(trx_scope) && (trn_ctx->rw_ha_count(trx_scope) > 1))
	error = tc_log->prepare(thd, all);
	...
	// Commit 阶段
	if (error \|\| (error = tc_log->commit(thd, all))) {ha_rollback_trans(thd, all);
	error = 1;
	goto end;
	}
	}

	\|mysql_execute_command
	\|--trans_commit
	\|----ha_commit_trans
	\|------MYSQL_BIN_LOG::prepare

	// 开启 binlog prepare 和 innodb prepare
	\|--------ha_prepare_low

	// Binlog prepare：获取上一个事务最大的 sequence number 工夫戳
	\|----------binlog_prepare

	// innodb prepare
	\|----------innobase_xa_prepare
	\|------------trx_prepare_for_mysql

	// 1. 调用 trx_prepare_low
	// 2. 事务状态设置为 Prepared
	// 3. 开释 RC 及以下隔离级别的 GAP Lock
	// 4. 刷盘 Redo（已推延到 Commit 阶段的 Flush stage）\|--------------trx_prepare
	\|----------------trx_prepare_low

	// 1. 将 undo log segment 的状态从 TRX_UNDO_ACTIVE 批改为 TRX_UNDO_PREPARED
	// 2. undo log 写入事务 XID
	\|------------------trx_undo_set_state_at_prepare

	int MYSQL_BIN_LOG::ordered_commit(THD *thd, bool all, bool skip_commit) {

	/*
	Stage #0: 保障从实例的 SQL 线程依照 Relay log 的事务程序进行提交
	*/
	if (Commit_order_manager::wait_for_its_turn_before_flush_stage(thd) \|\|
	ending_trans(thd, all) \|\|
	Commit_order_manager::get_rollback_status(thd)) {if (Commit_order_manager::wait(thd)) {return thd->commit_error;}
	}

	/*
	Stage #1: flushing transactions to binary log

	While flushing, we allow new threads to enter and will process
	them in due time. Once the queue was empty, we cannot reap
	anything more since it is possible that a thread entered and
	appointed itself leader for the flush phase.
	*/

	if (change_stage(thd, Commit_stage_manager::BINLOG_FLUSH_STAGE, thd, nullptr,
	&LOCK_log)) {DBUG_PRINT("return", ("Thread ID: %u, commit_error: %d", thd->thread_id(),
	thd->commit_error));
	return finish_commit(thd);
	}

	THD wait_queue = nullptr, final_queue = nullptr;
	mysql_mutex_t *leave_mutex_before_commit_stage = nullptr;
	my_off_t flush_end_pos = 0;
	bool update_binlog_end_pos_after_sync;

	// Flush 阶段次要的解决逻辑
	flush_error =
	process_flush_stage_queue(&total_bytes, &do_rotate, &wait_queue);

	if (flush_error == 0 && total_bytes > 0)
	/*
	flush binlog cache 到 file cache
	*/
	flush_error = flush_cache_to_file(&flush_end_pos);

	// 前面依据 sync_binlog 参数决定更新 binlog pos 的地位并播送 Binlog 更新信号
	update_binlog_end_pos_after_sync = (get_sync_period() == 1);

	/*
	If the flush finished successfully, we can call the after_flush
	hook. Being invoked here, we have the guarantee that the hook is
	executed before the before/after_send_hooks on the dump thread
	preventing race conditions among these plug-ins.
	*/
	if (flush_error == 0) {const char *file_name_ptr = log_file_name + dirname_length(log_file_name);
	assert(flush_end_pos != 0);
	/*
	插桩调用 after_flush，将曾经 flush 的 binlog file 和 position 注册到半同步复制插件中，用于后续比照 slave 应答承受到的 binlog position。*/
	if (RUN_HOOK(binlog_storage, after_flush,
	(thd, file_name_ptr, flush_end_pos))) {LogErr(ERROR_LEVEL, ER_BINLOG_FAILED_TO_RUN_AFTER_FLUSH_HOOK);
	flush_error = ER_ERROR_ON_WRITE;
	}

	// 如果 sync_binlog!=1，在 flush stage 更新 binlog 位点并播送 update 信号，从库的 Dump 线程能够由此感知 Binlog 的更新
	if (!update_binlog_end_pos_after_sync) update_binlog_end_pos();}


	int MYSQL_BIN_LOG::process_flush_stage_queue(my_off_t *total_bytes_var,
	bool *rotate_var,
	THD **out_queue_var) {

	int no_flushes = 0;
	my_off_t total_bytes = 0;
	mysql_mutex_assert_owner(&LOCK_log);
	// 依据 innodb_flush_log_at_trx_commit 参数进行 redo log 的刷盘操作
	THD *first_seen = fetch_and_process_flush_stage_queue();

	// 调用 get_server_sidno() 和 Gtid_state::get_automatic_gno 生成 GTID
	assign_automatic_gtids_to_flush_group(first_seen);
	/* Flush thread caches to binary log. */
	for (THD *head = first_seen; head; head = head->next_to_commit) {Thd_backup_and_restore switch_thd(current_thd, head);
	/*
	flush binlog_cache_mngr 的 stmt_cache 和 trx_cache。flush trx_cache：- 生成 last_committed 和 sequence_number
	- flush GTID log event
	- 将 trx_cache 中的数据 flush 到 binlog cache 中
	- 筹备提交事务后的 Binlog pos
	- 递增 prepread XID
	*/
	std::pair<int, my_off_t> result = flush_thread_caches(head);
	total_bytes += result.second;
	if (flush_error == 1) flush_error = result.first;
	#ifndef NDEBUG
	no_flushes++;
	#endif
	}

	*out_queue_var = first_seen;
	*total_bytes_var = total_bytes;
	if (total_bytes > 0 &&
	(m_binlog_file->get_real_file_size() >= (my_off_t)max_size \|\|
	DBUG_EVALUATE_IF("simulate_max_binlog_size", true, false)))
	*rotate_var = true;
	#ifndef NDEBUG
	DBUG_PRINT("info", ("no_flushes:= %d", no_flushes));
	no_flushes = 0;
	#endif
	return flush_error;
	}


	// 获取并清空 BINLOG_FLUSH_STAGE 和 COMMIT_ORDER_FLUSH_STAGE 队列，flush 事务到磁盘；不再阻塞 slave 的 preserve commit order 的执行
	\|fetch_and_process_flush_stage_queue

	// 存储引擎层将 prepare 状态的 redo log 依据 innodb_flush_log_at_trx_commit 参数刷盘
	\|--ha_flush_logs
	\|----innobase_flush_logs
	\|------log_buffer_flush_to_disk

	/*
	Stage #2: Syncing binary log file to disk
	*/

	if (change_stage(thd, Commit_stage_manager::SYNC_STAGE, wait_queue, &LOCK_log,
	&LOCK_sync)) {DBUG_PRINT("return", ("Thread ID: %u, commit_error: %d", thd->thread_id(),
	thd->commit_error));
	return finish_commit(thd);
	}

	/*
	- sync_counter：commit group 的数量
	- get_sync_period()：获取 sync_binlog 参数的值
	- 如果 sync stage 队列中的 commit group 大于等于 sync_binlog 的值，以后 leader 就调用 fsync()进行刷盘操作（sync_binlog_file(false)），在 sync 之前可能会进行期待，期待更多的 commit group 入队，期待的工夫为 binlog_group_commit_sync_no_delay_count 或 binlog_group_commit_sync_delay，默认都为 0。- 如果 sync stage 队列中的 commit group 小于 sync_binlog 的值，以后 leader 不会调用 fsync()进行刷盘也不会期待
	- 如果 sync_binlog 为 0，每个 commit group 都会触发期待动作，然而不会 sync
	- 如果 sync_binlog 为 1，每个 commit group 都会触发期待动作，且会 sync
	*/
	if (!flush_error && (sync_counter + 1 >= get_sync_period()))
	Commit_stage_manager::get_instance().wait_count_or_timeout(
	opt_binlog_group_commit_sync_no_delay_count,
	opt_binlog_group_commit_sync_delay, Commit_stage_manager::SYNC_STAGE);

	final_queue = Commit_stage_manager::get_instance().fetch_queue_acquire_lock(Commit_stage_manager::SYNC_STAGE);

	if (flush_error == 0 && total_bytes > 0) {DEBUG_SYNC(thd, "before_sync_binlog_file");
	std::pair<bool, bool> result = sync_binlog_file(false);
	sync_error = result.first;
	}

	/*
	如果 sync_binlog==1, 在 sync stage 阶段更新 binog 位点，并播送 update 信号，从库的 Dump 线程能够由此感知 Binlog 的更新（位点在 flush stage 中的 process_flush_stage_queue()
	\|--flush_thread_caches()
	\|-----set_trans_pos()函数中设置）*/
	if (update_binlog_end_pos_after_sync && flush_error == 0 && sync_error == 0) {
	THD *tmp_thd = final_queue;
	const char *binlog_file = nullptr;
	my_off_t pos = 0;

	while (tmp_thd != nullptr) {if (tmp_thd->commit_error == THD::CE_NONE) {tmp_thd->get_trans_fixed_pos(&binlog_file, &pos);
	}
	tmp_thd = tmp_thd->next_to_commit;
	}

	if (binlog_file != nullptr && pos > 0) {update_binlog_end_pos(binlog_file, pos);
	}
	}

	DEBUG_SYNC(thd, "bgc_after_sync_stage_before_commit_stage");

	leave_mutex_before_commit_stage = &LOCK_sync;

	/*
	Stage #3: Commit all transactions in order.
	*/
	commit_stage:
	/* binlog_order_commits：是否进行 order commit，即放弃 redo 和 binlog 的提交程序统一 */
	if ((opt_binlog_order_commits \|\| Clone_handler::need_commit_order()) &&
	(sync_error == 0 \|\| binlog_error_action != ABORT_SERVER)) {
	if (change_stage(thd, Commit_stage_manager::COMMIT_STAGE, final_queue,
	leave_mutex_before_commit_stage, &LOCK_commit)) {DBUG_PRINT("return", ("Thread ID: %u, commit_error: %d", thd->thread_id(),
	thd->commit_error));
	return finish_commit(thd);
	}
	THD *commit_queue =
	Commit_stage_manager::get_instance().fetch_queue_acquire_lock(Commit_stage_manager::COMMIT_STAGE);
	DBUG_EXECUTE_IF("semi_sync_3-way_deadlock",
	DEBUG_SYNC(thd, "before_process_commit_stage_queue"););

	if (flush_error == 0 && sync_error == 0)
	/* after_sync hook */
	sync_error = call_after_sync_hook(commit_queue);

	/*
	Commit 阶段的次要解决逻辑
	*/
	process_commit_stage_queue(thd, commit_queue);

	/**
	* After commit stage
	*/
	if (change_stage(thd, Commit_stage_manager::AFTER_COMMIT_STAGE,
	commit_queue, &LOCK_commit, &LOCK_after_commit)) {DBUG_PRINT("return", ("Thread ID: %u, commit_error: %d", thd->thread_id(),
	thd->commit_error));
	return finish_commit(thd);
	}

	THD *after_commit_queue =
	Commit_stage_manager::get_instance().fetch_queue_acquire_lock(Commit_stage_manager::AFTER_COMMIT_STAGE);
	/* after_commit hook */
	process_after_commit_stage_queue(thd, after_commit_queue);

	final_queue = after_commit_queue;
	mysql_mutex_unlock(&LOCK_after_commit);
	} else {if (leave_mutex_before_commit_stage)
	mysql_mutex_unlock(leave_mutex_before_commit_stage);
	if (flush_error == 0 && sync_error == 0)
	sync_error = call_after_sync_hook(final_queue);
	}


	/* 播送 m_stage_cond_binlog 信号变量，唤醒挂起的 follower */
	Commit_stage_manager::get_instance().signal_done(final_queue);
	DBUG_EXECUTE_IF("block_leader_after_delete", {const char action[] = "now SIGNAL leader_proceed";
	assert(!debug_sync_set_action(thd, STRING_WITH_LEN(action)));
	};);

	/*
	Finish the commit before executing a rotate, or run the risk of a
	deadlock. We don't need the return value here since it is in
	thd->commit_error, which is returned below.
	*/
	(void)finish_commit(thd);
	DEBUG_SYNC(thd, "bgc_after_commit_stage_before_rotation");

	return thd->commit_error == THD::CE_COMMIT_ERROR;
	}

	void MYSQL_BIN_LOG::process_commit_stage_queue(THD thd, THD first) {mysql_mutex_assert_owner(&LOCK_commit);
	#ifndef NDEBUG
	thd->get_transaction()->m_flags.ready_preempt =
	true; // formality by the leader
	#endif
	for (THD *head = first; head; head = head->next_to_commit) {
	DBUG_PRINT("debug", ("Thread ID: %u, commit_error: %d, commit_pending: %s",
	head->thread_id(), head->commit_error,
	YESNO(head->tx_commit_pending)));
	DBUG_EXECUTE_IF(
	"block_leader_after_delete",
	if (thd != head) {DBUG_SET("+d,after_delete_wait"); };);
	/*
	If flushing failed, set commit_error for the session, skip the
	transaction and proceed with the next transaction instead. This
	will mark all threads as failed, since the flush failed.

	If flush succeeded, attach to the session and commit it in the
	engines.
	*/
	#ifndef NDEBUG
	Commit_stage_manager::get_instance().clear_preempt_status(head);
	#endif
	/*
	更新全局的 m_max_committed_transaction（用作后续事务的 last_committed），并初始本事务上下文的 sequence number
	*/
	if (head->get_transaction()->sequence_number != SEQ_UNINIT) {mysql_mutex_lock(&LOCK_replica_trans_dep_tracker);
	m_dependency_tracker.update_max_committed(head);
	mysql_mutex_unlock(&LOCK_replica_trans_dep_tracker);
	}
	/*
	Flush/Sync error should be ignored and continue
	to commit phase. And thd->commit_error cannot be
	COMMIT_ERROR at this moment.
	*/
	assert(head->commit_error != THD::CE_COMMIT_ERROR);
	Thd_backup_and_restore switch_thd(thd, head);
	bool all = head->get_transaction()->m_flags.real_commit;
	assert(!head->get_transaction()->m_flags.commit_low \|\|
	head->get_transaction()->m_flags.ready_preempt);<br> // Binlog Commit、Innodb Commit
	::finish_transaction_in_engines(head, all, false);
	DBUG_PRINT("debug", ("commit_error: %d, commit_pending: %s",
	head->commit_error, YESNO(head->tx_commit_pending)));
	}

	/*
	锁定 sidno，更新整组事务的 executed_gtid
	- 如果没开启 binlog，@@GLOBAL.GTID_PURGED 的值是从 executed_gtid 获取的，此时 @@GLOBAL.GTID_PURGED 的值和 @@GLOBAL.GTID_EXECUTED 永远是统一的，就不须要在记录 lost_gtids
	- 如果开启了 binlog，然而未开启 log_replica_updates，slave 的 SQL 线程或 slave worker 线程
	将本身的 GTID 更新到 executed_gtids、lost_gtids
	*/
	gtid_state->update_commit_group(first);

	for (THD *head = first; head; head = head->next_to_commit) {Thd_backup_and_restore switch_thd(thd, head);
	auto all = head->get_transaction()->m_flags.real_commit;
	// 只针对内部 XA 事务，在存储引擎层将事务标记为 Prepared
	trx_coordinator::set_prepared_in_tc_in_engines(head, all);
	/*
	在存储引擎层提交之后，递加 Prepared 状态下的 XID 计数器
	*/
	if (head->get_transaction()->m_flags.xid_written) dec_prep_xids(head);
	}
	}

	\|::finish_transaction_in_engines
	\|--trx_coordinator::commit_in_engines
	\|----ha_commit_low

	// Binlog 层提交什么也不做（空函数）\|------binlog_commit

	// 存储引擎层提交
	\|------innobase_commit
	\|--------innobase_commit_low
	\|----------trx_commit_for_mysql

	// 为长久化 GTID 提前调配 update undo segment
	\|------------trx_undo_gtid_add_update_undo

	// 更新数据字典中被批改表的 update_time 工夫
	\|------------trx_update_mod_tables_timestamp

	// 调配 Mini-transaction handle 和 buffer
	\|------------trx_commit

	// 提交 mini-transaction
	\|--------------trx_commit_low
	\|----------------trx_write_serialisation_history

	// 更新 undo 状态：// 对于 insert 状态从 TRX_UNDO_ACTIVE 批改为 TRX_UNDO_TO_FREE
	// update 批改为 TRX_UNDO_TO_PURGE
	// 如果事务为 update 还须要将 rollback segments 调配 trx no，并将其增加到 purge 队列中
	\|------------------trx_undo_set_state_at_finish

	// 将 update undo log header 增加到 history list 结尾开释一些内存对象;
	\|------------------trx_undo_update_cleanup

	// 在零碎事务表记录 binlog 位点
	\|------------------trx_sys_update_mysql_binlog_offset
	\|----------------trx_commit_in_memory

	//- 敞开 mvcc read view
	//- 长久化 GTID
	//- 开释 insert undo log
	//- 唤醒后盾线程开始干活，如：master thread、purge thread、page_cleaner

	bool Commit_stage_manager::enroll_for(StageID stage, THD *thd,
	mysql_mutex_t *stage_mutex,
	mysql_mutex_t *enter_mutex) {
	// 如果队列为空，线程就是 leader
	thd->rpl_thd_ctx.binlog_group_commit_ctx().assign_ticket();
	bool leader = this->append_to(stage, thd);

	/*
	如果 FLUSH stage 队列（(BINLOG_FLUSH_STAGE 或 COMMIT_ORDER_FLUSH_STAGE）不为空，此线程就不能成为 leader。leader
	须要获取 enter_mutex
	*/
	if (leader) {if (stage == COMMIT_ORDER_FLUSH_STAGE) {leader = m_queue[BINLOG_FLUSH_STAGE].is_empty();
	/*
	leader 转换的逻辑。session 的队列有 5 种：- Binlog flush queue: flush redo 并写 Binlog File
	- Commit order flush queue: 针对 commit order 的事务，然而会参加 group commit 的结尾局部，直到引擎层的 flush。- Sync queue: sync transaction
	- Commit queue: 提交事务
	- After commit queue: 调用事务的 after_commit hook
	*/
	} else if (stage == BINLOG_FLUSH_STAGE && // 以后线程是 BINLOG_FLUSH_STAGE 中的第一个线程；然而 COMMIT_ORDER_FLUSH_STAGE
	// 曾经有了 leader，此时以后线程会挂起，期待 COMMIT_ORDER_FLUSH_STAGE 的 leader 的信号唤醒
	!m_queue[COMMIT_ORDER_FLUSH_STAGE].is_empty()) {
	/*
	以后事务是 binlog queue 中的第一个线程，然而在 commit order queue 中曾经有了一个 leader。此时以后线程会作为 leader，而 commit order leader 会转变为 follower。扭转 leader 的起因是 commit order leader 不能作为 binlog 线程的 leader，因为 commit order threads
	必须在 binlog threads 操作完之前来到 commit group。转变 leader 为 followers 的步骤如下：1. commit order thread 首先进入 flush stage，并成为 commit order leader。2. commit order leader 尝试获取 stage mutex，这可能会须要一些工夫，比方 mutex 曾经被上一个
	commit group 的 leader 获取。3. 在此期间，一个 binlog 线程进入了 flush stage。它须要期待来自 commit order leader 的信号。4. commit order leader 获取了 stage mutex，而后它会查看是否有 binlog thread 进入了 flush stage，如果发现了就转变 leader。5. commit order leader 给 binlog leader 发送一个信号，并成为 follower，期待 commit 的实现（和其余 follower 的行为统一）。6. binlog leader 被 commit order leader 的信号唤醒并执行 group commit。*/
	CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("before_binlog_leader_wait");
	while (thd->tx_commit_pending)
	mysql_cond_wait(&m_stage_cond_leader,
	&m_queue_lock[BINLOG_FLUSH_STAGE]);
	}
	}

	unlock_queue(stage);

	/*
	告诉下一个组提交事务进入队列
	*/
	if (stage == BINLOG_FLUSH_STAGE) {Commit_order_manager::finish_one(thd);
	CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("after_binlog_leader_wait");
	} else if (stage == COMMIT_ORDER_FLUSH_STAGE) {Commit_order_manager::finish_one(thd);
	}

	/*
	当进入第一个 stage 时，能够不必获取 stage mutex
	*/
	if (stage_mutex && need_unlock_stage_mutex) mysql_mutex_unlock(stage_mutex);

	/*
	如果队列非空，以后线程作为 follower 期待 leader 解决队列
	*/
	if (!leader) {CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("before_follower_wait");
	mysql_mutex_lock(&m_lock_done);
	#ifndef NDEBUG
	thd->get_transaction()->m_flags.ready_preempt = true;
	if (leader_await_preempt_status) mysql_cond_signal(&m_cond_preempt);
	#endif
	// tx_commit_pending：还有事务 commit 操作未实现
	while (thd->tx_commit_pending) {if (stage == COMMIT_ORDER_FLUSH_STAGE) {mysql_cond_wait(&m_stage_cond_commit_order, &m_lock_done);
	} else {
	// follower 线程在此处挂起，期待 leader 提交事务实现后被唤醒
	mysql_cond_wait(&m_stage_cond_binlog, &m_lock_done);
	}
	}

	mysql_mutex_unlock(&m_lock_done);
	return false;
	}

	#ifndef NDEBUG
	if (stage == Commit_stage_manager::SYNC_STAGE)
	DEBUG_SYNC(thd, "bgc_between_flush_and_sync");
	#endif

	bool need_lock_enter_mutex = false;
	if (leader && enter_mutex != nullptr) {
	/*
	如果因为在轮替 Binlog 时曾经获取了 LOCK_log，就不在须要获取 enter_mutex。*/
	need_lock_enter_mutex = !(mysql_bin_log.is_rotating_caused_by_incident &&
	enter_mutex == mysql_bin_log.get_log_lock());

	if (need_lock_enter_mutex)
	mysql_mutex_lock(enter_mutex);
	else
	mysql_mutex_assert_owner(enter_mutex);
	}

	// leader 转换的逻辑
	if (stage == COMMIT_ORDER_FLUSH_STAGE) {
	CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("after_commit_order_thread_becomes_leader");
	lock_queue(stage);

	if (!m_queue[BINLOG_FLUSH_STAGE].is_empty()) {if (need_lock_enter_mutex) mysql_mutex_unlock(enter_mutex);

	THD *binlog_leader = m_queue[BINLOG_FLUSH_STAGE].get_leader();
	binlog_leader->tx_commit_pending = false;

	mysql_cond_signal(&m_stage_cond_leader);
	unlock_queue(stage);

	mysql_mutex_lock(&m_lock_done);
	/* wait for signal from binlog leader */
	CONDITIONAL_SYNC_POINT_FOR_TIMESTAMP("before_commit_order_leader_waits_for_binlog_leader");
	while (thd->tx_commit_pending)
	mysql_cond_wait(&m_stage_cond_commit_order, &m_lock_done);
	mysql_mutex_unlock(&m_lock_done);

	leader = false;
	return leader;
	}
	}

	return leader;
	}

关于mysql:源码分析-MySQL-的-commit-是怎么-commit-的

一、Prepare 阶段

1. Binlog Prepare

2. InnoDB Prepare

二、Commit 阶段

1. Stage 0

2. Flush Stage

3. Sync Stage

4. Commit Stage

Prepare 阶段

Commit 阶段

Flush 阶段

SYNC 阶段

COMMIT 阶段

阶段转换

Just My Socks（注册教程 内含优惠码）

Just My Socks（注册教程内含优惠码）