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MySQL Database Administrator

Boost Your Quick Knowledge in MySQL DBA Work, Concepts, Tips and Trick

Wednesday, 26 June 2019

After change the user privileges, When Changes Take Effect ?

You can modify the user privileges with two methods ...

Changes Take Effect- Immediately

If you modify the grant tables indirectly using an account-management statement (Examples include GRANT, REVOKE, SET PASSWORD, and RENAME USER), the server notices these changes and loads the grant tables into memory again immediately. 

Changes Take Effect - After issuing FLUSH PRIVILEGES or restart MySQL

If you modify the grant tables directly using statements such as INSERT, UPDATE, or DELETE , the changes have no effect on privilege checking until you either tell the server to reload the tables or restart it.

To tell the server to reload the grant tables, perform a flush-privileges operation. This can be done by issuing a FLUSH PRIVILEGES statement or by executing a mysqladmin flush-privileges or mysqladmin reload command.

A grant table reload affects privileges for each existing client session as follows:

Table and column privilege changes take effect with the client's next request.

Database privilege changes take effect the next time the client executes a USE db_name statement.

Note:
Client applications may cache the database name; thus, this effect may not be visible to them without actually changing to a different database.

Global privileges and passwords are unaffected for a connected client. These changes take effect only in sessions for subsequent connections.

Reference and Copyright to Reference Manual

Friday, 14 June 2019

MAX_USED_CONNECTIONS PER USER/ACCOUNT

How many connections can be opened concurrently against my MySQL database can be configured and checked with the following command:

[mysqld]
max_connections= 2500
SHOW GLOBAL VARIABLES LIKE 'max_connections';

Variable_name
Value
max_connections
2500

We can check the status of this limit as below..

SHOW STATUS LIKE 'max_used%';

Variable_name
Value
Max_used_connections
587
Max_used_connections_time
2019-06-05 16:07:28

But MySQL instances may be configured with many different applications (= database's/schema's) and thus many different users.It is a bit more complicated to find out which of these users have connected how many times concurrently. We can limit the maximum concurrent connection per user with:

[mysqld]
max_user_connections= 500

SHOW GLOBAL VARIABLES LIKE 'max_user_connections';

Variable_name
Value
max_user_connections
500

OR

Further we can limit one specific user with:

GRANT USAGE ON *.* TO 'alok'@'%' WITH MAX_CONNECTIONS_PER_HOUR 1000 MAX_USER_CONNECTIONS 700;

and check with: 

SELECT User, Host, max_connections, max_user_connections FROM mysql.user;

User
Host
max_connections
max_user_connections
alok
172.31.28.36
0
700
alok
%
1000
700
root
localhost
0
0

Now if you want to check Max_used_connections per user wise currently we have no chance to check the same.

This feature request was opened at MySQL bug (#77888) report https://bugs.mysql.com/bug.php?id=77888

Implementing Max_used_connections per user:-


I will show you how to implement a custom table for storing max_used_connections &max_used_tim user wise.
Create Table max_used_connections in database mysql

USE mysql;
CREATE TABLE `max_used_connections` (
  `USER` char(16) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `HOST` char(60) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  `CONNECTION` bigint(20) NOT NULL,
  `MAX_USED_CONNECTIONS` bigint(20) NOT NULL,
  `MAX_USED_TIME` varchar(50)DEFAULT NULL,
  UNIQUE KEY `USER` (`USER`,`HOST`) USING HASH
) ENGINE=MEMORY DEFAULT CHARSET=utf8;


Now create an event to update the table “max_used_connections” and store the required status.

CREATE DEFINER=root@localhost EVENT mysql.max_used_connections
ON SCHEDULE EVERY 5 SECOND
DO
INSERT INTO mysql.max_used_connections
SELECT user, host, current_connections,current_connections as CONNECTION ,'' MAX_USED_TIME FROM performance_schema.accounts 
WHERE user IS NOT NULL AND host IS NOT NULL ON DUPLICATE KEY
UPDATE max_used_connections = IF(current_connections > max_used_connections, current_connections, max_used_connections),
CONNECTION = current_connections ,
MAX_USED_TIME = IF(max_used_connections > current_connections, MAX_USED_TIME,now());

NOTE: Event Scheduler must be Enable to achieve this feature.
Now you can check the current status of max_used_connections per user as below.



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