MySQL tuning -- 02 -- slow query log

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Slow query log

1. Enable the slow query log parameter

1.1 Turn on slow_query_log

1.2 modify long_query_time threshold

2. View the number of slow queries

3. Slow query log analysis tool ：mysqldumpslow

3.1 give an example

3.2 Common references for work ：

4. Turn off slow query log

MySQL There are two ways for the server to stop the slow query log function ：

The way 1： Permanent way

The way 2： Temporary way

5. Delete slow query log

Slow query case

Table structure

CREATE TABLE `person_info_large` (  
    `id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,  
    `account` VARCHAR (10),   
    `name` VARCHAR (20),  
    `area` VARCHAR (20),  
    `title` VARCHAR (20), 
    `motto` VARCHAR (50),
    PRIMARY KEY (`id`),  
    UNIQUE(`account`),
    KEY `index_area_title`(`area`,`title`) 
) ENGINE = INNODB AUTO_INCREMENT = 1 DEFAULT CHARSET = utf8  

run

• The data here is 200W strip . Note the table structure , Just remember which fields have indexes , The following analysis will focus on this table .
  
  This 3.36s Not the actual execution time , The actual execution time has to be slow. Check the log Query_time Parameters

Slow query log files

You can see Query_time: 6.337729s, More than the 1s, So it will be recorded

• Be careful ： Some slow queries are executing , As a result, the database has been overloaded , However, due to the slow speed, the query has not been executed yet , Therefore, the slow query log cannot see any statements , You can use show processlist Command to view the slow query being executed .show processlist Show which threads are running , If there is PROCESS jurisdiction , You can see all threads . otherwise , You can only see the current session thread .

Parameter description

• Time： The time when the slow query occurred
• Query_time： Query time
• Lock_time： Time waiting to lock the watch
• Rows_sent： The number of rows returned by the statement
• Rows_exanined： Number of rows read from the storage engine during statement execution

concerns

Focus on : Rows_exanined Number of scanning lines / Rows_sent Returns the number of rows