性能模式监视事务。在事件层级中，等待事件嵌套在阶段事件中，阶段事件嵌套在语句事件中，语句事件嵌套在事务事件中。The Performance Schema instruments transactions. Within the event hierarchy, wait events nest within stage events, which nest within statement events, which nest within transaction events.

这些表用于存储事务事件：These tables store transaction events:

以下各节描述了事务事件表。还有一些汇总表，它们汇总了有关事务事件的信息；请参阅 第 29.12.20.5 节，“事务汇总表”。The following sections describe the transaction event tables. There are also summary tables that aggregate information about transaction events; see Section 29.12.20.5, “Transaction Summary Tables”.

有关这三个事务事件表之间关系的更多信息，请参阅 第 29.9 节，“当前和历史事件的性能模式表”。For more information about the relationship between the three transaction event tables, see Section 29.9, “Performance Schema Tables for Current and Historical Events”.

配置事务事件收集Configuring Transaction Event Collection

要控制是否收集事务事件，请设置相关设备和消费者的状态：To control whether to collect transaction events, set the state of the relevant instruments and consumers:

transaction 工具以及 events_transactions_current 和 events_transactions_history 事务消费者默认是启用的：The transaction instrument and the events_transactions_current and events_transactions_history transaction consumers are enabled by default:

mysql> SELECT NAME, ENABLED, TIMED
       FROM performance_schema.setup_instruments
       WHERE NAME = 'transaction';
+-------------+---------+-------+
| NAME        | ENABLED | TIMED |
+-------------+---------+-------+
| transaction | YES     | YES   |
+-------------+---------+-------+
mysql> SELECT *
       FROM performance_schema.setup_consumers
       WHERE NAME LIKE 'events_transactions%';
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| events_transactions_current      | YES     |
| events_transactions_history      | YES     |
| events_transactions_history_long | NO      |
+----------------------------------+---------+

要在服务器启动时控制事务事件的收集，请在您的 my.cnf 文件中使用如下行：To control transaction event collection at server startup, use lines like these in your my.cnf file:

要在运行时控制事务事件的收集，请更新 setup_instruments 和 setup_consumers 表：To control transaction event collection at runtime, update the setup_instruments and setup_consumers tables:

要仅收集特定事务事件表的事务事件，请启用 transaction 工具，同时仅启用与所需表对应的事务消费者。To collect transaction events only for specific transaction event tables, enable the transaction instrument but only the transaction consumers corresponding to the desired tables.

有关配置事件收集的更多信息，请参见第 29.3 节，“性能模式启动配置”，以及第 29.4 节，“性能模式运行时配置”。For additional information about configuring event collection, see Section 29.3, “Performance Schema Startup Configuration”, and Section 29.4, “Performance Schema Runtime Configuration”.

事务边界Transaction Boundaries

在 MySQL 服务器中，事务通过以下语句显式开始：In MySQL Server, transactions start explicitly with these statements:

START TRANSACTION | BEGIN | XA START | XA BEGIN

事务也会隐式开始。例如，当autocommit 系统变量启用时，每条语句的开始都会启动一个新事务。Transactions also start implicitly. For example, when the autocommit system variable is enabled, the start of each statement starts a new transaction.

当autocommit 被禁用时，紧跟在已提交事务之后的第一条语句标志着新事务的开始。随后执行的语句都是该事务的一部分，直到事务被提交。When autocommit is disabled, the first statement following a committed transaction marks the start of a new transaction. Subsequent statements are part of the transaction until it is committed.

事务可通过以下语句显式结束：Transactions explicitly end with these statements:

COMMIT | ROLLBACK | XA COMMIT | XA ROLLBACK

事务也可以隐式结束，例如执行 DDL 语句、锁定语句和服务器管理语句时。Transactions also end implicitly, by execution of DDL statements, locking statements, and server administration statements.

在下面的讨论中，对 START TRANSACTION 的引用也适用于 BEGIN、XA START 以及 XA BEGIN。类似地，对 COMMIT 和 ROLLBACK 的引用分别适用于 XA COMMIT 和 XA ROLLBACK。In the following discussion, references to START TRANSACTION also apply to BEGIN, XA START, and XA BEGIN. Similarly, references to COMMIT and ROLLBACK apply to XA COMMIT and XA ROLLBACK, respectively.

性能模式定义了与服务器类似的事务边界。事务事件的开始和结束与服务器中相应的状态转换紧密匹配：The Performance Schema defines transaction boundaries similarly to that of the server. The start and end of a transaction event closely match the corresponding state transitions in the server:

这种方法有一些微妙的含义：There are subtle implications to this approach:

举例说明，考虑以下场景：To illustrate, consider the following scenario:

1. SET autocommit = OFF;
2. CREATE TABLE t1 (a INT) ENGINE = InnoDB;
3. START TRANSACTION;                       -- Transaction 1 START
4. INSERT INTO t1 VALUES (1), (2), (3);
5. CREATE TABLE t2 (a INT) ENGINE = MyISAM; -- Transaction 1 COMMIT
                                            -- (implicit; DDL forces commit)
6. INSERT INTO t2 VALUES (1), (2), (3);     -- Update nontransactional table
7. UPDATE t2 SET a = a + 1;                 -- ... and again
8. INSERT INTO t1 VALUES (4), (5), (6);     -- Write to transactional table
                                            -- Transaction 2 START (implicit)
9. COMMIT;                                  -- Transaction 2 COMMIT

从服务器的角度来看，当表t2创建时，事务 1 结束。尽管中间对非事务表进行了更新，但事务 2 直到访问事务型表时才开始。From the perspective of the server, Transaction 1 ends when table t2 is created. Transaction 2 does not start until a transactional table is accessed, despite the intervening updates to nontransactional tables.

从性能模式的角度来看，当服务器进入活动事务状态时，事务 2 开始。语句 6 和 7 不包含在事务 2 的范围内，这与服务器将事务写入二进制日志的方式一致。From the perspective of the Performance Schema, Transaction 2 starts when the server transitions into an active transaction state. Statements 6 and 7 are not included within the boundaries of Transaction 2, which is consistent with how the server writes transactions to the binary log.

事务检测Transaction Instrumentation

三个属性定义事务：Three attributes define transactions:

为了降低事务检测的复杂性，并确保收集到的事务数据提供完整、有意义的结果，所有事务均独立于访问模式、隔离级别或自动提交模式进行检测。To reduce complexity of the transaction instrumentation and to ensure that the collected transaction data provides complete, meaningful results, all transactions are instrumented independently of access mode, isolation level, or autocommit mode.

要选择性地检查事务历史，请使用事务事件表中的属性列：ACCESS_MODE、ISOLATION_LEVEL 和 AUTOCOMMIT。To selectively examine transaction history, use the attribute columns in the transaction event tables: ACCESS_MODE, ISOLATION_LEVEL, and AUTOCOMMIT.

可以通过多种方式降低事务监控的成本，例如根据用户、账户、主机或线程（客户端连接）启用或禁用事务监控。The cost of transaction instrumentation can be reduced various ways, such as enabling or disabling transaction instrumentation according to user, account, host, or thread (client connection).

事务与嵌套事件Transactions and Nested Events

事务事件的父事件是启动该事务的事件。对于显式启动的事务，这包括START TRANSACTION和COMMIT AND CHAIN语句。对于隐式启动的事务，它是上一事务结束后使用事务引擎的第一条语句。The parent of a transaction event is the event that initiated the transaction. For an explicitly started transaction, this includes the START TRANSACTION and COMMIT AND CHAIN statements. For an implicitly started transaction, it is the first statement that uses a transactional engine after the previous transaction ends.

一般来说，事务是事务期间启动的所有事件的顶层父级，包括明确结束事务的语句，例如 COMMIT 和 ROLLBACK。例外是隐式结束事务的语句，例如 DDL 语句，在这种情况下，必须在执行新语句之前提交当前事务。In general, a transaction is the top-level parent to all events initiated during the transaction, including statements that explicitly end the transaction such as COMMIT and ROLLBACK. Exceptions are statements that implicitly end a transaction, such as DDL statements, in which case the current transaction must be committed before the new statement is executed.

事务和存储程序Transactions and Stored Programs

事务和存储程序事件的关系如下：Transactions and stored program events are related as follows:

事务和保存点Transactions and Savepoints

保存点语句作为单独的语句事件记录。事务事件包括在事务期间发出的SAVEPOINT、ROLLBACK TO SAVEPOINT和RELEASE SAVEPOINT语句的单独计数器。Savepoint statements are recorded as separate statement events. Transaction events include separate counters for SAVEPOINT, ROLLBACK TO SAVEPOINT, and RELEASE SAVEPOINT statements issued during the transaction.

事务和错误Transactions and Errors

在事务中发生的错误和警告会记录在语句事件中，但不会记录在相应的事务事件中。这包括事务特定的错误和警告，例如对非事务性表的回滚或 GTID 一致性错误。Errors and warnings that occur within a transaction are recorded in statement events, but not in the corresponding transaction event. This includes transaction-specific errors and warnings, such as a rollback on a nontransactional table or GTID consistency errors.