MySQL Slow query analysis

To view the slow query log for MySQL, first turn on the slow query record for MySQL.

Check that the MySQL slow query record is turned on,

Mysql> Show variables like ' slow_query% '; +---------------------+--------------------------------+| variable_name | Value |+---------------------+--------------------------------+| Slow_query_log | On | | Slow_query_log_file | /var/log/mysql/mysql-slow.log |+---------------------+--------------------------------+

Slow_query_log on means that slow query logging is turned on slow_query_log_file indicates the location of the slow query log file record

Mysql> Show variables like ' long_query_time '; +-----------------+----------+| variable_name | Value |+-----------------+----------+| Long_query_time | 2.000000 |+-----------------+----------+

Indicates that a query over 2 seconds is a slow query and will be logged into the slow query log.

How to analyze slow query log?

MySQL comes with a tool for parsing slow query logs mysqldumpslow

Mysqldumpslow–s c–t Slow-query.log

The specific parameters are set as follows:

-S means the sort by how, C, T, L, R are in accordance with the number of records, time, query time, the number of records returned to sort, AC, at, AL, AR, indicating the corresponding flashbacks;

-T is the meaning of top, followed by the data to return the first number of bars;

-G can write regular expression matching, case insensitive.

The count:2978 statement appeared 2,978 times;

Time=59.72s (177857s) The maximum time to execute 59.72s, the total time spent 177857s;

lock=0.0s (2s) Wait for the maximum time to lock 0s, the cumulative waiting lock time is 2s;

rows=1.0 (2857) The maximum number of rows sent to the client is 1.0, and the cumulative function sent to the client is 2857;

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Included operation commands for MySQL connection number

1.mysql> Show status like ' threads% ';

+-------------------+-------+

| variable_name | Value |

+-------------------+-------+

| threads_cached | 58 |

| threads_connected |   57 | # # #这个数值指的是打开的连接数

| threads_created | 3676 |

| threads_running |   4 | # # #这个数值指的是激活的连接数, this value is generally much lower than the connected value

+-------------------+-------+

The threads_connected is the same as the show processlist result, indicating the current number of connections. To be exact, threads_running is the current number of concurrent

2. This is the maximum number of connections that are currently set for the query database

Mysql> Show variables like '%max_connections% ';

+-----------------+-------+

| variable_name | Value |

+-----------------+-------+

| max_connections | 1000 |

+-----------------+-------+

The maximum number of connections to the database can be set in/ETC/MY.CNF

[Mysqld]

max_connections = 1000

The 3.max_connections parameter can be used to control the maximum number of connections for a database:

Mysql> Show variables like '%connect% ';

+--------------------------+-------------------+

| variable_name | Value |

+--------------------------+-------------------+

| character_set_connection | Latin1 |

| collation_connection | Latin1_swedish_ci |

| Connect_timeout | 10 |

|                   Init_connect | |

| max_connect_errors | 10 |

| max_connections | 4000 |

| max_user_connections | 0 |

+--------------------------+-------------------+

MySQL Slow query analysis