MySQL log

MySQL journal

In any database , There are all kinds of logs , It records all aspects of database work , To help database administrators track events that have occurred in the database ,MySQL No exception

Classification of logs

Error log 、 Binary log (binlog)、 Query log 、 Slow query log

Error log

 The error log is MySQL One of the most important logs in , He recorded MySQL When starting and stopping , 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 , You can check this log first .
 The log is enabled by default , The default storage directory is MySQL Data directory for , The default log file name is hostname.err(hostname It's the host name )
 View log location command : show variables like '%log_error%';
 see mysql Whether it is turned on binlog journal : show variables like '%log_bin%';
 see binlog Format of log :show variables like '%binlog_format%';

Binary log (binlog)

 The binary log records all DDL( Database definition language ) Statement and DML( Data operation language ) sentence , But it does not include data query statements , This log plays an extremely important role in data recovery in case of disaster ,MySQL Master-slave replication of , Through this binlog Realized .
 Binary log ,MySQL8.0 It is on by default , Low version of the MySQL You need to start through the configuration file , And configuration MySQl Format of log ,windows System :my.ini,linux System :my.cnf

--  Configuration on binlog journal , The file prefix of the log is mysqlbin ---> The generated file name is as follows :mysqlbin.000001,mysqlbin.000002
    log_bin = mysqlbin
--  Configure binary log format 
	binlog_format = STATEMENT

 Log format 
statement: The log format is recorded in the log file sql sentence , Every one of the items that modify the data sql Will be recorded in the log file , adopt mysql Provided mysqlbinlog Tools , You can see the text of each statement clearly , When master and slave copy , Slave Library (slave) Will resolve the log to the original text , And execute it again from the library .
row: The log format records the data changes of each line in the log file , Instead of recording sql sentence , Ultimate Reality : perform sql sentence :update tb_name set status=1 , If it is statement Log format , A line will be recorded in the log sql file , If it is row, Because it's updating the whole table , That is to say, every line of record will change ,row The data changes of each line will be recorded in the format log .
mixed: Mixed up statement and row Two formats .

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 set the configuration 
--  This option is used to open the query log , Optional value :0 or 1;0 On behalf of closed  1 Representative opens 
set general_log=1
--  Set the file name of the log , If not specified , The default filename is host_name.log
general_log_file=file_name

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 ,long_query_time The default is 10 second , The minimum is 0, Precision can be adjusted to microseconds 
--  This parameter is used to control whether the slow query log is enabled   Value for 0 and 1,1 Representative opens  0 On behalf of closed 
slow_query_log=1
--  This parameter is used to specify the file name of the slow query log 
slow_query_log_file=slow_query.log
--  This option is used to configure the query time limit , After this time, it will be considered as slow query , Will need to log , Default 10s
long_query_time=10
    
--  Check whether the slow log is enabled 
show variables like '%slow_query_log%'
--  View the timeout of slow query 
show variables like '%long_query_time%'

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