7. ENGINES

7. ENGINES

ENGINES表提供有关存储引擎的信息。 这对于检查是否支持存储引擎或查看默认引擎是什么特别有用。

INFORMATION_SCHEMA Name	SHOW Name
ENGINE	Engine
SUPPORT	Support
COMMENT	Comment
TRANSACTIONS	Transactions
XA	XA
SAVEPOINTS	Savepoints

ENGINES表有以下列：

• ENGINE：存储引擎名称
• SUPPORT：服务器对存储引擎的支持级别，如下表所示。

值	含义
YES	引擎受支持且处于活动状态
DEFAULT	类似YES，并且表示是默认引擎
NO	不支持引擎
DISABLED	引擎受支持但已被禁用

值NO表示编译服务器时不支持引擎，因此无法在运行时启用它。

出现DISABLED值的原因是服务器是使用禁用引擎的选项启动的，或者因为没有给出启用它所需的所有选项。 在后一种情况下，错误日志应包含指示禁用该选项的原因。 请参见第“错误日志”。

如果服务器已编译为支持存储引擎，您可能还会看到DISABLED，但是使用--skip-engine_name选项启动。 对于NDB存储引擎，DISABLED表示服务器是在支持NDB Cluster的情况下编译的，但未使用--ndbcluster选项启动。

所有MySQL服务器都支持MyISAM表。 无法禁用MyISAM。

• COMMENT：存储引擎的简要说明。
• TRANSACTIONS：存储引擎是否支持XA事务。
• SAVEPOINTS：存储引擎是否支持保存点。

该ENGINES表是一个非标准INFORMATION_SCHEMA表。

mysql> select * from information_schema.engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| ENGINE             | SUPPORT | COMMENT                                                        | TRANSACTIONS | XA   | SAVEPOINTS |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)

mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.01 sec)