What happens if the MySQL disk is full? I really met you!

Use the command to find that the disk utilization rate is 100% 了 , There are dozens of megabytes left .

A series of divine operations

Backup database , Delete the instance 、 Delete database tables 、 restart mysql service , As a result, no disk space was released .

What do I do

I searched a lot of resources on the Internet , Said to do disk defragmentation . as a result of datafree It takes up too much space . You can go through this sql see .

SELECT CONCAT(TRUNCATE(SUM(data_length)/1024/1024,2),'MB') AS data_size,
CONCAT(TRUNCATE(SUM(max_data_length)/1024/1024,2),'MB') AS max_data_size,
CONCAT(TRUNCATE(SUM(data_free)/1024/1024,2),'MB') AS data_free,
CONCAT(TRUNCATE(SUM(index_length)/1024/1024,2),'MB') AS index_size
FROM information_schema.tables WHERE TABLE_NAME = 'datainfo';

This is a later picture , There is no previous picture left , At that time, it showed the data_free All have reached 20 individual G.

Online recommendations are as follows , Break up the forms .

ALTER TABLE datainfo ENGINE=InnoDB;
ANALYZE TABLE datainfo;

optimize table datainfo;

deadlock ：

View the database version as 5.562 I won't support it inodb, Or choose to upgrade the database . Just then , There's bad news , The form has been deleted , But the disk space still hasn't been released . So the way to defragment your tables is not going to work , Because the watch is gone ...

Later, the divine operation

1、 Command view mysql The location of the installation and the location of the configuration file

mysql 1118 945 0 14:28 ? 00:00:00 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin --log-error=/var/log/mysqld.log --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/lib/mysql/mysql.sock

2、 close mysql

service mysql stop  

3、 Delete datadir In the catalog ibdata1、ib_logfile0 ib_logfile1 These documents

4、 Move mysql Start parameter of

mv /etc/my.cnf ./abc

5、 Restart mysql Found disk space free service mysql start

The disk space is finally free

The next step is to restore the database

1、 use navicate Backup tools , Database backup

After the backup was successful , Generate psc file .200409141055.psc

2、 Create a new database instance , Set database name and character set

3、 Then restore the backup database , Click restore

4、 Start restoring After the first restore, we found that the database tables were successfully created after the restore , But there's no data in the table . Later, I searched the Internet and found that it was , Stop when you make a mistake . So the restored configuration was changed , Restore again . It was set up like this before

Restore as a transaction , Stop when you make a mistake . Change configuration Restore again , The data in the database has , And verify that there is no problem .

Problem solving

mysql The cause of fragmentation

（1） The storage of the table will be fragmented , Whenever a line is deleted , The space will be left blank , And in a period of time a large number of delete operations , This will make the empty space larger than the space used to store the contents of the list ;

（2） When the insert operation is performed ,MySQL Will try to use blank space , But if a blank space has not been occupied by data of the right size , It still can't be completely occupied , It's a fragment ;

（3） When MySQL When scanning data , The object it scans is actually the upper limit of the list's capacity requirement , That is, the part of the area where the data is written to the peak position ;

The advantages of debris removal :

Reduce the access to the table IO, Improve mysql performance , Free up table space and reduce disk space utilization

Be careful

1.MySQL The official advice is not to ( Every hour or every day ) Defragment , Generally according to the actual situation , Just do it weekly or monthly ( We are in the early hours of every month 4 Spot cleaning mysql Table fragments under all instances ).

2. stay OPTIMIZE TABLE In operation ,MySQL Will lock the table . therefore , This operation must be carried out at a time when the website is less visited .

3. clear student Of 105 Ten thousand data , OPTIMIZE TABLE library .student; Local testing requires 37 second .

Self testing

You can use this sentence to see your own system of datafree big show table status from Table name ;