MySQL enable slow query

One 、 What is slow query ？ Why should there be slow queries ？

The so-called slow query , It's a kind of execution select When inquiring , The execution efficiency is very slow SQL sentence .

In the high concurrency scenario, we need to make all the SQL Statement execution is the fastest , Let users have a good sense of experience . And we have no way to know SQL When the statement is issued in high concurrency, the query is slow , At this time, we need to set or enable slow query , And then use SQL Statements to optimize ;

Usually we will use explain To analyze this SQL, Then you can index the appropriate fields , Conduct SQL Optimize ;

Two 、 Several ways to enable slow query

1. adopt MySQL Database open slow query :

set global slow_query_log=on
set global long_query_time=3;
set global log_queries_not_using_indexes=on

 slow_query_log： The slow query log logging on( Turn on )/off( close );

 long_query_time:SQL Statement execution time exceeds 3 Is considered a slow query statement , Recorded in the slow query log

log_queries_not_using_indexes: Query whether the unused index is enabled to record slow query logs  on( Turn on )/off( close );

2. modify MySQL The configuration file

Temporarily open （ Restart failure ）

-------------------------------------------------------------------

long_query_time = 10
log-slow-queries = /var/lib/mysql/mysql-slow.log

Permanent open （ Restart does not fail ）

--------------------------------------------------------------------
[mysqld]
slow_query_log = ON
slow_query_log_file = /var/lib/mysql/tmp_slow.log     //linux
long_query_time = 1

Mysql View slow query log _Chen_leilei The blog of -CSDN Blog _mysql How to view slow query logs