[Architecture] MySQL Log File-slow query log

As the name suggests, the slow query log records a query with a long execution time. You can set a threshold value and record all SQL statements with a running time exceeding this value to the slow query log file.

As the name suggests, the slow query log records a query with a long execution time. You can set a threshold value and record all SQL statements with a running time exceeding this value to the slow query log file.

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[Architecture] MySQL Log File-slow query log

[Date:] Source: Linux community Author: linwaterbin [Font:]

As the name suggests, slow query logs record queries with a long execution time.

You can set a threshold to record all SQL statements whose running time exceeds this threshold to the slow query log file.

The threshold value can be set using the long_query_time parameter. The default value is 10 seconds.

It is required that the running time is exactly the same as long_query_time and will not be recorded.

In the source code, it is determined that the value is greater than long_query_time, not greater than or equal

Mysql> show variables like 'Log _ slow_queries ';
+ ------------------ + ------- +
| Variable_name | Value |
+ ------------------ + ------- +
| Log_slow_queries | ON |
+ ------------------ + ------- +
1 row in set (0.00 sec)

Mysql> show variables like 'long _ query_time ';
+ ----------------- + ----------- +
| Variable_name | Value |
+ ----------------- + ----------- +
| Long_query_time | 10.000000 |
+ ----------------- + ----------- +
1 row in set (0.00 sec)

Another parameter related to slow query logs is log_queries_not_using_indexes.

If the running SQL statement does not use an index, MySQL also records this statement to the slow query log file.

Mysql> show variables like 'Log _ queries_not_using_indexes ';
+ ------------------------------- + ------- +
| Variable_name | Value |
+ ------------------------------- + ------- +
| Log_queries_not_using_indexes | OFF |
+ ------------------------------- + ------- +
1 row in set (0.00 sec)

Here, I have not enabled it, but I need to remind you that if you modify this parameter online, no error is reported, but it does not take effect.

MySQL also provides the tool program mysqldumpslow for analyzing full query logs to help MySQL DBAs solve possible performance problems.

Example: Obtain the TOP-5 SQL statement:

[Mysql @ localhost bin] $./mysqldumpslow-s al-n 5/home/mysql/log/slow. log

Reading mysql slow query log from/home/mysql/log/slow. log
Count: 1 Time = 0.00 s (0 s) Lock = 0.00 s (0 s) Rows = 0.0 (0), 0users @ 0 hosts

0

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