Database Administration Statements

MySQL 5.5 Reference Manual  /  SQL Statement Syntax  /  Database Administration Statements  /  Table Maintenance Statements

optimize table 优化表

mysql> ? optimize table
Name: 'OPTIMIZE TABLE'
Description:
Syntax:
OPTIMIZE [NO_WRITE_TO_BINLOG | LOCAL] TABLE tbl_name [, tbl_name] ...

NO_WRITE_TO_BINLOG 抑制sql语句被写入到binlog

Reorganizes the physical storage of table data and associated index data, to reduce storage space and improve I/O efficiency when accessing the table. The exact changes made to each table depend on the storage engine used by that table.
重新组织表数据和相关索引数据的物理存储，减少存储空间、提升访问表时的I/O效率，对每张表的确切的改变取决于该表使用的存储引擎。

Use OPTIMIZE TABLE in these cases, depending on the type of table:
在这些场景下优化表，取决于表类型：
o After doing substantial insert, update, or delete operations on an InnoDB table that has its own .ibd file because it was created with the innodb_file_per_table option enabled. The table and indexes are reorganized, and disk space can be reclaimed for use by the operating
system.
o 在一张有自己的.ibd文件的InnoDB表（创建时启用innodb_file_per_table选项）执行了大量的插入、更新或删除操作之后，通过执行optimize table，这个表会被重新组织，磁盘空间可以被操作系统再次使用。（聚簇索引）

o After deleting a large part of a MyISAM or ARCHIVE table, or making many changes to a MyISAM or ARCHIVE table with variable-length rows (tables that have VARCHAR, VARBINARY, BLOB, or TEXT columns). Deleted rows are maintained in a linked list and subsequent INSERT operations reuse old row positions. You can use OPTIMIZE TABLE to reclaim the unused space and to defragment the data file. After extensive changes to a table, this statement may also improve performance of statements that use the table, sometimes significantly.
o 在删除了一个MyISAM或ARCHIVE表的一大部分、或对包含可变长度行的MyISAM ARCHIVE表（包含VARCHAR VARBINARY BLOB TEXT列的表）做了很多改变，被删除的行通过一个linked list来维护，随后的插入操作重新使用旧的行位置。你可以使用OPTIMIZE TABLE 来收回未使用的空间、对数据文件碎片整理。在大量的改变之后，这个语句也可以显著提升使用这张表的语句的性能。

This statement requires SELECT and INSERT privileges for the table.
这个语句要求具有对该表的select和insert权限。

OPTIMIZE TABLE is also supported for partitioned tables. For information about using this statement with partitioned tables and table partitions, see
http://dev.mysql.com/doc/refman/5.5/en/partitioning-maintenance.html.

URL: http://dev.mysql.com/doc/refman/5.5/en/optimize-table.html

OPTIMIZE TABLE 也支持分区表。

Kill Statements 停止SQL或连接

mysql> ? kill
Name: 'KILL'
Description:
Syntax:
KILL [CONNECTION | QUERY] processlist_id

Each connection to mysqld runs in a separate thread. You can kill a thread with the KILL processlist_id statement.
每个到mysqld服务的连接都运行在分离的线程。你可以使用kill processlist_id 语句杀死一个线程。

Thread processlist identifiers can be determined from the ID column of the INFORMATION_SCHEMA.PROCESSLIST table, the Id column of SHOW
PROCESSLIST output, and the PROCESSLIST_ID column of the Performance Schema threads table. The value for the current thread is returned by the CONNECTION_ID() function.
线程识别符可以从INFORMATION_SCHEMA.PROCESSLIST的ID列、show processlist的输出、Performance Schema的threads表的PROCESSLIST_ID得到。当前线程的ID可以从 select connection_id()得到。

KILL permits an optional CONNECTION or QUERY modifier:
kill 允许 CONNECTION 和 QUERY 这两个可选的修饰符
o KILL CONNECTION is the same as KILL with no modifier: It terminates the connection associated with the given processlist_id, after terminating any statement the connection is executing.
   Kill CONNECTION 等同于 Kill 不加修饰符：它终止了语句之后，又终止了连接。
o KILL QUERY terminates the statement the connection is currently executing, but leaves the connection itself intact.
   Kill QUERY 终止了正在执行的语句，但保留了连接本身。

If you have the PROCESS privilege, you can see all threads. If you have the SUPER privilege, you can kill all threads and statements. Otherwise, you can see and kill only your own threads and statements.
如果你有process权限，你可以看到所有线程。如果你有super权限，你可以杀死所有线程和语句。否则，你只可以看到和杀死自己的线程和语句。

You can also use the mysqladmin processlist and mysqladmin kill commands to examine and kill threads.
你也可以使用mysqladmin processlist 和 mysqladmin kill 来检测和杀死线程。

*Note*: You cannot use KILL with the Embedded MySQL Server library because the embedded server merely runs inside the threads of the host application. It does not create any connection threads of its own.
你不可以将kill语句用在嵌入式Mysql服务，因为嵌入式服务只运行在主机应用的线程中，本身并没有创建任何连接线程。
URL: http://dev.mysql.com/doc/refman/5.5/en/kill.html