参数文件：告诉Mysql实例数据库文件的位置，定义参数。

日志文件：Mysql实例对某种条件作出的响应写入文件，这个文件就是日志文件，

常见的日志文件有：错误日志、二进制日志、慢查询日志以及查询日志。

socket文件：采用Unix域套接字方式进行连接时会用到的文件，

一般，我们在本地用mysql命令行连入数据库就是采用的该方式。

pid文件：Mysql实例的进程ID文件。

Mysql表结构文件：用来存放表结构定义的文件

存储引擎文件：每个表存储引擎都会有个文件来保存该引擎相关的数据，

这些数据主要是数据和索引数据。

mysql> select * from GLOBAL_VARIABLES where VARIABLE_NAME like 'innodb_buffer%'\G;

*************************** . row ***************************

 VARIABLE_NAME: INNODB_BUFFER_POOL_FILENAME

VARIABLE_VALUE: ib_buffer_pool

*************************** . row ***************************

 VARIABLE_NAME: INNODB_BUFFER_POOL_DUMP_NOW

VARIABLE_VALUE: OFF

*************************** . row ***************************

 VARIABLE_NAME: INNODB_BUFFER_POOL_LOAD_NOW

VARIABLE_VALUE: OFF

*************************** . row ***************************

 VARIABLE_NAME: INNODB_BUFFER_POOL_LOAD_ABORT

VARIABLE_VALUE: OFF

*************************** . row ***************************

 VARIABLE_NAME: INNODB_BUFFER_POOL_SIZE

VARIABLE_VALUE:

*************************** . row ***************************

 VARIABLE_NAME: INNODB_BUFFER_POOL_DUMP_AT_SHUTDOWN

VARIABLE_VALUE: OFF

*************************** . row ***************************

 VARIABLE_NAME: INNODB_BUFFER_POOL_LOAD_AT_STARTUP

VARIABLE_VALUE: OFF

*************************** . row ***************************

 VARIABLE_NAME: INNODB_BUFFER_POOL_INSTANCES

VARIABLE_VALUE: 

mysql> show variables like 'innodb_buffer%'\G;

set global|session variable_name=value或者
set @@global|@@session.variable_name=value语句

mysql> show variables like 'log_error'\G;

*************************** . row ***************************

Variable_name: log_error

        Value: /var/lib/mydata/iZeu234q4mamqhZ.err

 row in set (0.00 sec)

mysql> show variables like '%long%'\G;

*************************** . row ***************************

Variable_name: long_query_time

        Value: 10.000000

# mysqldumpslow --help

Usage: mysqldumpslow [ OPTS... ] [ LOGS... ]

Parse and summarize the MySQL slow query log. Options are

  --verbose    verbose

  --debug      debug

  --help       write this text to standard output

  -v           verbose

  -d           debug

  -s ORDER     what to sort by (al, at, ar, c, l, r, t), 'at' is default

                al: average lock time

                ar: average rows sent

                at: average query time

                 c: count

                 l: lock time

                 r: rows sent

                 t: query time

  -r           reverse the sort order (largest last instead of first)

  -t NUM       just show the top n queries

  -a           don't abstract all numbers to N and strings to 'S'

  -n NUM       abstract numbers with at least n digits within names

  -g PATTERN   grep: only consider stmts that include this string

  -h HOSTNAME  hostname of db server for *-slow.log filename (can be wildcard),

               default is '*', i.e. match all

  -i NAME      name of server instance (if using mysql.server startup script)

  -l           don't subtract lock time from total time

mysql> show create table slow_log\G;

*************************** . row ***************************

       Table: slow_log

Create Table: CREATE TABLE `slow_log` (

  `start_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,

  `user_host` mediumtext NOT NULL,

  `query_time` time NOT NULL,

  `lock_time` time NOT NULL,

  `rows_sent` int() NOT NULL,

  `rows_examined` int() NOT NULL,

  `db` varchar() NOT NULL,

  `last_insert_id` int() NOT NULL,

  `insert_id` int() NOT NULL,

  `server_id` int() unsigned NOT NULL,

  `sql_text` mediumtext NOT NULL,

  `thread_id` bigint() unsigned NOT NULL

) ENGINE=CSV DEFAULT CHARSET=utf8 COMMENT='Slow log'

 row in set (0.00 sec)

mysql> show variables like 'log_output'\G;

*************************** . row ***************************

Variable_name: log_output

        Value: FILE

 row in set (0.00 sec)

mysql> select sleep();

+----------+

| sleep() |

+----------+

|         |

+----------+

 row in set (5.00 sec)

mysql > alter table slow_log engine=myisam;

Variable_name: general_log

        Value: OFF

*************************** . row ***************************

Variable_name: general_log_file

        Value: /var/lib/mydata/xxx.log

 log-bin=mysql-bin

-rw-rw----  mysql mysql        Jul   : mysql-bin.

-rw-rw----  mysql mysql        Jul   : mysql-bin.

-rw-rw----  mysql mysql        Jul   : mysql-bin.

-rw-rw----  mysql mysql        Jul   : mysql-bin.

-rw-rw----  mysql mysql     Jul  : mysql-bin.

-rw-rw----  mysql mysql        Jul  : mysql-bin.

-rw-rw----  mysql mysql        Jul  : mysql-bin.

-rw-rw----  mysql mysql        Jul  : mysql-bin.

-rw-rw----  mysql mysql        Jul  : mysql-bin.

mysql> show variables like 'pid_file';

+---------------+----------------------------+

| Variable_name | Value                      |

+---------------+----------------------------+

| pid_file      | /var/run/mysqld/mysqld.pid |

+---------------+----------------------------+

 row in set (0.01 sec)