How to enable MySQL’s slow query function

MySQL is currently the most widely used relational database management system, and enabling slow queries for MySQL allows us to better understand and optimize query operations. In this article, we will discuss how to enable MySQL's slow query function and introduce some common query optimization techniques.

1. What is MySQL slow query?

First of all, we need to understand what MySQL slow query is. When we perform MySQL query operations, if the query takes too long, the system will record these query operations in the slow query log. Generally speaking, a query operation whose execution time exceeds a specified threshold (such as 1 second) is considered a slow query.

By recording slow queries, we can understand which queries take more time to execute, so we can take appropriate optimization measures to improve query efficiency.

2. How to enable MySQL slow query?

Next, we will introduce how to enable the MySQL slow query function. It should be noted that turning on slow query will increase the system load and resource consumption, so we should turn it on and use it with caution.

1. First, we need to add the following code to the MySQL configuration file:

slow_query_log = 1
slow_query_log_file = /path/to/slow-query.log
long_query_time = 1

Among them, slow_query_log and long_query_time indicate turning on the slow query function and specifying the slow query threshold, in seconds. slow_query_log_file represents the path of the slow query log file and can be customized.

2. Then, we need to restart the MySQL service for the configuration to take effect:

sudo service mysql restart

3. Finally, we can use the following Command to view the slow query log:

sudo tail -f /path/to/slow-query.log

When we perform a query operation, if the query time exceeds long_query_time, it will is logged to the slow query log file.

3. Common query optimization techniques

In addition to turning on the slow query function, we can also adopt the following common query optimization techniques to improve query efficiency:

1. Use Index: Index can speed up WHERE conditions and JOIN operations and improve query efficiency. However, too many indexes will increase system burden and occupy storage space, so indexes should be used reasonably according to the actual situation.
2. Optimize query statements: Using appropriate query statements can avoid data scanning and row-by-row comparison and improve query efficiency. For example, use LIMIT to limit the number of data items, avoid using SELECT * to query all fields, etc.
3. Avoid full table scan: Full table scan will greatly reduce query efficiency and should be avoided as much as possible. You can use the EXPLAIN command to analyze query statements to find out the cause of slow queries.
4. Sub-database and table: When the amount of data is too large, you can consider dispersing the data into different databases or tables to achieve horizontal expansion, reduce the burden on a single database or table, and improve query efficiency.
5. Use cache: For some frequent query results, you can use cache to improve query efficiency. For example, use caching tools such as memcached and Redis.

4. Summary

Turning on MySQL slow query can help us identify operations with low query efficiency and take corresponding optimization measures. Although turning on slow query will increase the system load and resource consumption, adopting appropriate query optimization techniques can effectively improve query efficiency and ensure application performance.

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