[MySQL] log

journal

1. Error log

The error log is MySQL One of the most important logs in , It records when MySQL When the service starts and stops , As well as information about any serious errors in the running process of the server . When there is any failure of the database that results in the failure of normal use , It is recommended to view this log first . The log is on by default , The default storage directory is /var/log/, The default log file name is mysqld.log.

#  Check the error log 
# /var/log/mysqlld.log
show variables like '%log_error%';

2. Binary log

Introduce

The binary log records all DDL sentence （ Data definition language ） and DML sentence （ Data manipulation language ）, But it does not include query statements （ Such as ：SELECT、SHOW）. stay MySQL8 In the version , Binary log is on by default , The functions of binary log are as follows ：

• Data recovery in case of disaster
• MySQL Master-slave replication of .

#  View binary logs 
# /var/lib/mysql/binlog
show variables like '%log_bin%';

• log_bin_basename： The base name of the binary log of the current database server （ Prefix ）, The specific binary file name needs to be in this basename Add a number on the basis of （ Number from 000001 Start ）.
• log_bin_index： Index file of binary log , Record the binary file associated with the current server .

Format

If we need to configure the format of binary log , Only need /etc/my.cnf Middle configuration binlog_format Parameters can be .

#  View binary log format 
show variables like '%binlog_format%';

see

Because logs are stored in binary , Can't read directly , You need to use the binary log query tool mysqlbinlog Check it out. .

Delete

For busy business systems , The binary log data generated every day is huge , If you don't clear it for a long time , It will take up a lot of disk space .

#  Check the expiration time of binary log 
show variables like '%binlog_expire_logs_seconds%';

Query log

The query log records all the operation statements of the client , Binary log does not contain query data SQL sentence . By default , The query log is not opened . If you need to open the query log , You can modify MySQL Configuration file for /etc/my.cnf file . After the query log is turned on ,MySQL Data storage directory , That is to say /var/lib/mysql/ It will appear in the directory mysql_query.log file . After that, all the operations of adding, deleting, modifying and checking the client will be recorded in the log file , After a long run , The log file will be very large .

#  View query log 
show variables like '%general%';

Slow query log

The slow query log records that all execution times exceed the parameters long_query_time Set the value and the number of scan records is not less than min_examined_row_limit All of SQL Statement log , Default not on .long_query_time The default is 10 second , The minimum is 0, The precision can reach microseconds .

By default , Management statements will not be recorded , Queries that do not use indexes for lookup are also not recorded . have access to log_slow_admin_statements And change this behavior log_queries_not_using_indexes

After all the above parameters are configured , All need to be restarted MySQL The server can take effect .

Reference resources ：https://www.bilibili.com/video/BV1Kr4y1i7ru