Mysql：语法：事务管理

mysql的存储引擎有：事务型、非事务型 之分。

mysql支持本地事务——即 各个连接会话 可以自由控制事务的处理，mysql默认是事务自动提交模式。

不同的事务型引擎能够支持的事务功能 也不相同。

基本上mysql的innodb引擎是功能全面，支持事务特性最多的引擎！

 

set autocommit = {1 | 0} ：1为默认值——自动提交

 

start transaction | begin 开始事务

commit 提交事务

rollback 回滚事务

 

xa事务

保存点

 

SET TRANSACTION Syntax

SET [GLOBAL | SESSION] TRANSACTION ISOLATION LEVEL
  {
       READ UNCOMMITTED
     | READ COMMITTED
     | REPEATABLE READ
     | SERIALIZABLE
   }

This statement sets the transaction isolation level globally, for the current session, or for the next transaction:

• With the GLOBAL keyword, the statement sets the default transaction level globally for all subsequent sessions. Existing sessions are unaffected.

• With the SESSION keyword, the statement sets the default transaction level for all subsequent transactions performed within the current session.

• Without any SESSION or GLOBAL keyword, the statement sets the isolation level for the next (not started) transaction performed within the current session.

A change to the global default isolation level requires the SUPER privilege. Any session is free to change its session isolation level (even in the middle of a transaction), or the isolation level for its next transaction.

To set the global default isolation level at server startup, use the --transaction-isolation=level option to mysqld on the command line or in an option file. Values of level for this option use dashes rather than spaces, so the allowable values are READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE. For example, to set the default isolation level to REPEATABLE READ, use these lines in the [mysqld] section of an option file:

[mysqld]
transaction-isolation = REPEATABLE-READ

To determine the global and session transaction isolation levels at runtime, check the value of the tx_isolation system variable:

SELECT @@GLOBAL.tx_isolation, @@tx_isolation;

InnoDB supports each of the translation isolation levels described here using different locking strategies. The default level is REPEATABLE READ. For additional information about InnoDB record-level locks and how it uses them to execute various types of statements, see Section 13.6.8.4, “InnoDB Record, Gap, and Next-Key Locks”, and Section 13.6.8.6, “Locks Set by Different SQL Statements in InnoDB”.

The following list describes how MySQL supports the different transaction levels:

• READ UNCOMMITTED

  SELECT statements are performed in a nonlocking fashion, but a possible earlier version of a row might be used. Thus, using this isolation level, such reads are not consistent. This is also called a “dirty read.” Otherwise, this isolation level works like READ COMMITTED.

• READ COMMITTED

  A somewhat Oracle-like isolation level with respect to consistent (nonlocking) reads: Each consistent read, even within the same transaction, sets and reads its own fresh snapshot. See Section 13.6.8.2, “Consistent Nonlocking Reads”.

  For locking reads (SELECT with FOR UPDATE or LOCK IN SHARE MODE), InnoDB locks only index records, not the gaps before them, and thus allows the free insertion of new records next to locked records. For UPDATE and DELETE statements, locking depends on whether the statement uses a unique index with a unique search condition (such as WHERE id = 100), or a range-type search condition (such as WHERE id > 100). For a unique index with a unique search condition, InnoDB locks only the index record found, not the gap before it. For range-type searches, InnoDB locks the index range scanned, using gap locks or next-key (gap plus index-record) locks to block insertions by other sessions into the gaps covered by the range. This is necessary because “phantom rows” must be blocked for MySQL replication and recovery to work.

  Note

  In MySQL 5.1, if the READ COMMITTED isolation level is used or the innodb_locks_unsafe_for_binlog system variable is enabled, there is no InnoDB gap locking except for foreign-key constraint checking and duplicate-key checking. Also, record locks for nonmatching rows are released after MySQL has evaluated the WHERE condition.

  As of MySQL 5.1, if you use READ COMMITTED or enable innodb_locks_unsafe_for_binlog, you must use row-based binary logging.

• REPEATABLE READ

  This is the default isolation level for InnoDB. For consistent reads, there is an important difference from the READ COMMITTED isolation level: All consistent reads within the same transaction read the snapshot established by the first read. This convention means that if you issue several plain (nonlocking) SELECT statements within the same transaction, these SELECT statements are consistent also with respect to each other. See Section 13.6.8.2, “Consistent Nonlocking Reads”.

  For locking reads (SELECT with FOR UPDATE or LOCK IN SHARE MODE), UPDATE, and DELETE statements, locking depends on whether the statement uses a unique index with a unique search condition, or a range-type search condition. For a unique index with a unique search condition, InnoDB locks only the index record found, not the gap before it. For other search conditions, InnoDB locks the index range scanned, using gap locks or next-key (gap plus index-record) locks to block insertions by other sessions into the gaps covered by the range.

• SERIALIZABLE

  This level is like REPEATABLE READ, but InnoDB implicitly converts all plain SELECT statements to SELECT ... LOCK IN SHARE MODE if autocommit is disabled. If autocommit is enabled, the SELECT is its own transaction. It therefore is known to be read only and can be serialized if performed as a consistent (nonlocking) read and need not block for other transactions. (This means that to force a plain SELECT to block if other transactions have modified the selected rows, you should disable autocommit.)

 

不能被事务回滚的语句 ：一般DDL语句不能被事务回滚，你不应该在事务中包含此类语句

 

隐式提交的语句：一句话，如果没有什么特特殊的地方，mysql总是隐式提交，除非你想自行控制事务

The statements listed in this section (and any synonyms for them) implicitly end a transaction, as if you had done a COMMIT before executing the statement.

• 定义 或 修改 数据库对象的 DDL语句 ALTER DATABASE ... UPGRADE DATA DIRECTORY NAME, ALTER EVENT, ALTER PROCEDURE, ALTER TABLE, CREATE DATABASE, CREATE EVENT, CREATE INDEX, CREATE PROCEDURE, CREATE TABLE, DROP DATABASE, DROP EVENT, DROP INDEX, DROP PROCEDURE, DROP TABLE, RENAME TABLE, TRUNCATE TABLE.

• ALTER FUNCTION, CREATE FUNCTION and DROP FUNCTION also cause an implicit commit when used with stored functions, but not with UDFs. (ALTER FUNCTION can only be used with stored functions.)

  ALTER TABLE, CREATE TABLE,  DROP TABLE  临时表不会引起隐式提交

  The CREATE TABLE statement in InnoDB is processed as a single transaction. This means that a ROLLBACK from the user does not undo CREATE TABLE statements the user made during that transaction.

  Beginning with MySQL 5.1.3, ALTER VIEW, CREATE TRIGGER, CREATE VIEW, DROP TRIGGER, and DROP VIEW cause an implicit commit.

  Beginning with MySQL 5.1.15, CREATE TABLE ... SELECT causes an implicit commit before and after the statement is executed when you are creating nontemporary tables. (No commit occurs for CREATE TEMPORARY TABLE ... SELECT.) This is to prevent an issue during replication where the table could be created on the master after a rollback, but fail to be recorded in the binary log, and therefore not replicated to the slave. For more information, see Bug#22865.

• 会修改系统库 mysql 的操作. Beginning with MySQL 5.1.3, CREATE USER, DROP USER, and RENAME USER cause an implicit commit. Beginning with MySQL 5.1.23, GRANT, REVOKE, and SET PASSWORD statements cause an implicit commit.

• 事务控制和锁定语句. BEGIN, LOCK TABLES, SET autocommit = 1 (if the value is not already 1), START TRANSACTION, UNLOCK TABLES.

  UNLOCK TABLES commits a transaction only if any tables currently have been locked with LOCK TABLES. This does not occur for UNLOCK TABLES following FLUSH TABLES WITH READ LOCK because the latter statement does not acquire table-level locks.

  Transactions cannot be nested. This is a consequence of the implicit commit performed for any current transaction when you issue a START TRANSACTION statement or one of its synonyms.

  Statements that cause an implicit commit cannot be used in an XA transaction while the transaction is in an ACTIVE state.

  The BEGIN statement differs from the use of the BEGIN keyword that starts a BEGIN ... END compound statement. The latter does not cause an implicit commit. See Section 12.8.1, “BEGIN ... END Compound Statement Syntax”.

• 数据装载. LOAD DATA INFILE. Before MySQL 5.1.12, LOAD DATA INFILE caused an implicit commit for all storage engines. As of MySQL 5.1.12, it causes an implicit commit only for tables using the NDB storage engine. For more information, see Bug#11151.

• 系统管理语句. CACHE INDEX, LOAD INDEX INTO CACHE. Beginning with MySQL 5.1.10, ANALYZE TABLE, CHECK TABLE, OPTIMIZE TABLE, and REPAIR TABLE cause an implicit commit.