MySQL版本：5.7.23

在閑逛mysql時(shí)發(fā)現(xiàn)mysql庫(kù)的user表下有兩個(gè)賬戶比較特別：
mysql.session和mysql.sys

mysql> use mysql;
Database changed
mysql> show tables;
+---------------------------+
| Tables_in_mysql           |
+---------------------------+
| columns_priv              |
| db                        |
| engine_cost               |
| event                     |
| func                      |
| general_log               |
| gtid_executed             |
| help_category             |
| help_keyword              |
| help_relation             |
| help_topic                |
| innodb_index_stats        |
| innodb_table_stats        |
| ndb_binlog_index          |
| plugin                    |
| proc                      |
| procs_priv                |
| proxies_priv              |
| server_cost               |
| servers                   |
| slave_master_info         |
| slave_relay_log_info      |
| slave_worker_info         |
| slow_log                  |
| tables_priv               |
| time_zone                 |
| time_zone_leap_second     |
| time_zone_name            |
| time_zone_transition      |
| time_zone_transition_type |
| user                      |
+---------------------------+
31 rows in set (0.00 sec)

查一下user表里面都有哪些賬戶：

mysql> select user, host from user;
+---------------+-----------+
| user          | host      |
+---------------+-----------+
| mysql.session | localhost |
| mysql.sys     | localhost |
| root          | localhost |
+---------------+-----------+
3 rows in set (0.00 sec)

mysql.sys@localhost:
用于 sys schema中對(duì)象的定義。使用 mysql.sys 用戶可避免DBA重命名或者刪除root用戶時(shí)發(fā)生的問(wèn)題。該用戶已被鎖定，客戶端無(wú)法連接。
mysql.session@localhost:
插件內(nèi)部使用來(lái)訪問(wèn)服務(wù)器。該用戶已被鎖定，客戶端無(wú)法連接。root@localhost:
這個(gè)就是root賬號(hào)啦！其用于管理。該用戶擁有所有權(quán)限，可執(zhí)行任何操作。嚴(yán)格來(lái)說(shuō)，這個(gè)賬號(hào)不應(yīng)該被保留。root是MySQL的特權(quán)賬號(hào)，這個(gè)眾所周知，也帶來(lái)安全隱患。建議將root賬號(hào)禁用或者刪除，新建一個(gè)特權(quán)賬號(hào)用于管理。

在MySQL 5.6以前，我們通過(guò)show processlist\G命令查看系統(tǒng)中正在運(yùn)行的所有進(jìn)程：

mysql> show processlist;
+----+------+-----------+-------+---------+------+----------+------------------+
| Id | User | Host      | db    | Command | Time | State    | Info             |
+----+------+-----------+-------+---------+------+----------+------------------+
|  6 | root | localhost | mysql | Query   |    0 | starting | show processlist |
+----+------+-----------+-------+---------+------+----------+------------------+
1 row in set (0.00 sec)

從5.7開始，我們又可以通過(guò)sys.session表來(lái)查看系統(tǒng)正在運(yùn)行的所有進(jìn)程，而且該表中的記錄相processlist比較完善：

mysql> select * from sys.session\G
*************************** 1. row ***************************
                thd_id: 31
               conn_id: 6
                  user: NULL
                    db: mysql
               command: Query
                 state: Sending data
                  time: 0
     current_statement: select * from sys.session
     statement_latency: 1.79 ms
              progress: NULL
          lock_latency: 0 ps
         rows_examined: 0
             rows_sent: 0
         rows_affected: 0
            tmp_tables: 4
       tmp_disk_tables: 1
             full_scan: YES
        last_statement: NULL
last_statement_latency: NULL
        current_memory: 0 bytes
             last_wait: NULL
     last_wait_latency: NULL
                source: NULL
           trx_latency: NULL
             trx_state: NULL
        trx_autocommit: NULL
                   pid: 4612
          program_name: mysql
1 row in set (0.06 sec)

很顯然，select * from sys.session能得到更多的信息。

我這個(gè)是用root賬戶在mysql庫(kù)下執(zhí)行的命令，當(dāng)然你也可以去sys庫(kù)查看;

#表太多了，只寫出我們要的表
mysql> use sys;
Database changed
mysql> show tables;
+-----------------------------------------------+
| Tables_in_sys                                 |
+-----------------------------------------------+
|......                                         |
| processlist                                   |
|......                                         |
+-----------------------------------------------+

然后查看該表中的信息：

#數(shù)據(jù)行太多了，囧……
#只顯示一行吧
mysql> select * from processlist\G
*************************** 1. row ***************************
                thd_id: 1
               conn_id: NULL
                  user: sql/main
                    db: NULL
               command: NULL
                 state: NULL
                  time: 3262
     current_statement: NULL
     statement_latency: NULL
              progress: NULL
          lock_latency: NULL
         rows_examined: NULL
             rows_sent: NULL
         rows_affected: NULL
            tmp_tables: NULL
       tmp_disk_tables: NULL
             full_scan: NO
        last_statement: NULL
last_statement_latency: NULL
        current_memory: 0 bytes
             last_wait: NULL
     last_wait_latency: NULL
                source: NULL
           trx_latency: NULL
             trx_state: NULL
        trx_autocommit: NULL
                   pid: NULL
          program_name: NULL

mysql> select * from session\G
*************************** 1. row ***************************
                thd_id: 31
               conn_id: 6
                  user: NULL
                    db: sys
               command: Query
                 state: Sending data
                  time: 0
     current_statement: select * from session
     statement_latency: 1.31 ms
              progress: NULL
          lock_latency: 0 ps
         rows_examined: 0
             rows_sent: 0
         rows_affected: 0
            tmp_tables: 4
       tmp_disk_tables: 1
             full_scan: YES
        last_statement: NULL
last_statement_latency: NULL
        current_memory: 0 bytes
             last_wait: NULL
     last_wait_latency: NULL
                source: NULL
           trx_latency: NULL
             trx_state: NULL
        trx_autocommit: NULL
                   pid: 4612
          program_name: mysql
1 row in set (0.05 sec)

文章中部分內(nèi)容引用自
http://www.mamicode.com/info-detail-1301870.html
http://www.dbhelp.net/2017/11/29/mysql-5-7-%E6%96%B0%E5%A2%9E%E9%BB%98%E8%AE%A4%E8%B4%A6%E5%8F%B7-mysql-session%E5%92%8Cmysql-sys.html