1.查询数据库各个库大小
语法：
SELECT
TABLE_SCHEMA AS "库名",
TRUNCATE(SUM(`DATA_LENGTH`) / 1024 / 1024, 2) AS "表所占空间（MB）",
TRUNCATE(SUM(`INDEX_LENGTH`) / 1024 / 1024, 2) AS "索引所占空间（MB）",
TRUNCATE((SUM(`DATA_LENGTH`) + SUM(`INDEX_LENGTH`)) / 1024 / 1024,2) AS "空间累计（MB）"
FROM
information_schema.`TABLES`
GROUP BY `TABLE_SCHEMA`;
例子：
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MySQL connection id is 16891974
Server version: 5.6.28-cdb2016-log 20180130
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MySQL [(none)]> SELECT
-> TABLE_SCHEMA AS "库名",
-> TRUNCATE(SUM(`DATA_LENGTH`) / 1024 / 1024, 2) AS "表所占空间（MB）",
-> TRUNCATE(SUM(`INDEX_LENGTH`) / 1024 / 1024, 2) AS "索引所占空间（MB）",
-> TRUNCATE((SUM(`DATA_LENGTH`) + SUM(`INDEX_LENGTH`)) / 1024 / 1024,2) AS "空间累计（MB）"
-> FROM
-> information_schema.`TABLES`
-> GROUP BY `TABLE_SCHEMA`;
+----------------------+-------------------------+----------------------------+----------------------+
| 库名 | 表所占空间（MB） | 索引所占空间（MB） | 空间累计（MB） |
+----------------------+-------------------------+----------------------------+----------------------+
| test | 60653.62 | 29787.29 | 90440.92 |
2.查询并发
show global status like 'Threads%';
例子：
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MySQL connection id is 1868103
Server version: 5.7.18-txsql-log 20190203
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MySQL [(none)]> show global status like 'Threads%';
+-------------------+-------+
| Variable_name | Value |
+-------------------+-------+
| Threads_cached | 121 |
| Threads_connected | 202 |
| Threads_created | 326 |
| Threads_running | 2 |
+-------------------+-------+
4 rows in set (0.00 sec)
MySQL [(none)]>
3.查询从节点
语法：
show slave hosts;
例子：
MySQL [(none)]> show slave hosts;
+-----------+------+-------+-----------+--------------------------------------+
| Server_id | Host | Port | Master_id | Slave_UUID |
+-----------+------+-------+-----------+--------------------------------------+
| 6946 | | 20144 | 129415 | cc7d2390-2791-11ea-8185-b8599f4e4f29 |
| 129414 | | 20130 | 129415 | 7b302430-2790-11ea-be67-58f9875cd401 |
+-----------+------+-------+-----------+--------------------------------------+
2 rows in set (0.00 sec)
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