What does slow query refer to in MySQL

This article mainly introduces what the slow query in MySQL refers to. It is very detailed and has a certain reference value. Friends who are interested must finish it!

The method to analyze the query performance of MySQL statements not only uses EXPLAIN output execution plan, but also allows MySQL to record statements that exceed a specified time. We call a SQL statement query that exceeds a specified time as a "slow query".

MySQL slow query is to record slow SQL statements in the log, which needs to be turned on before it can be used.

Write in the configuration file my.cnf of MySQL:

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

Long_query_time refers to how long the SQL will be logged, in this case, 10 seconds.

The log-slow-queries setting writes the log there (in the example, the slow log will be written to the file / var/lib/mysql/mysql-slow.log). If it is empty, the system will give the slow log a hostname and add slow.log. If the parameter log-long-format is set, all queries that do not use the index will also be logged.

This is a very useful journal. It has little impact on performance (assuming that all queries are fast) and emphasizes the queries that need the most attention (missing indexes or indexes that are not best applied).

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