Improve performance by using MySQL query cache

With the increase in data volume and access, database performance issues have become a bottleneck for many websites. In many cases, database queries are one of the most resource-intensive operations on a website. As an open source relational database management system, MySQL has become the database of choice for many websites. In MySQL, query cache is a caching mechanism that can significantly improve query performance. This article will introduce how the MySQL query cache works and provide some practical suggestions that can help you better use the MySQL query cache to improve system performance.

What is MySQL query cache?

MySQL query cache is a caching mechanism provided by MySQL. Its function is to store the results of recently executed queries. When a query request arrives at the MySQL server, MySQL checks to see if any results stored in the cache match the request. If a matching result is found, MySQL directly returns the cached result without executing the query, thus saving the time and resources of executing the query.

MySQL query cache works as follows:

1. MySQL executes a query and stores the query and results in the cache.
2. When the query request arrives at the MySQL server again, MySQL checks whether there are query results with the same query parameters in the cache. If the results exist, return the cached results instead of executing the query.
3. If the query results are not in the cache, MySQL executes the query and stores the results in the cache for the next query.

It should be noted that in some cases, the MySQL query cache may have a negative impact on performance. For example, if query results are rarely reused, the space occupied by the cache may slow query performance. Additionally, if a query that updates the original table is used, MySQL will clear the result cache for that query, causing other results in the cache to be cleared as well.

How to use MySQL query cache?

You can enable MySQL query cache by following these steps:

1. Confirm that MySQL has correctly configured query cache parameters.

Query cache parameters refer to the MySQL system parameters that control the size and behavior of the cache, including the following parameters:

• query_cache_type: can take a value of 0, 1 or 2, Respectively means to disable the query cache, enable the query cache, or only enable the query cache and ignore SQL_NO_CACHE in all SELECT statements.
• query_cache_size: Specifies the maximum available space for the query cache. The default value is 0, which disables query caching. It is recommended to set the parameter value between 10% and 50% of the system memory.
• query_cache_limit: Specifies the maximum cache size of a single query result. The default value is 1MB, and it is recommended to adjust it according to the size of the query results and system memory conditions.

2. Confirm that caching is enabled in the SELECT statement.

Cache can be enabled by adding the SQL_CACHE keyword in the SELECT statement. An example is as follows:

SELECT SQL_CACHE * FROM table_name;

3. Monitor the effect of the cache.

Use the SHOW STATUS statement to view the query cache statistics, including the query cache hit rate, the space occupied by the cache, the number of times the cache has been cleared, etc. You can use these statistics to evaluate the impact of query caching on system performance.

Related practical suggestions

The following are some practical suggestions for using the MySQL query cache, which can help you make better use of the query cache to improve system performance.

1. Consider cache size carefully.

If the cache is too small, it may cause cache misses and waste time and resources executing queries. If the cache is too large, it may waste system resources and cause performance degradation. It is recommended to optimize the cache size based on the system load and query request patterns.

2. Avoid using non-constant expressions.

If the SELECT statement contains non-constant expressions, such as the NOW() function or variables, the query cache will ignore the cache and execute the query. Therefore, it is recommended to use constant expressions whenever possible to take advantage of the query cache.

3. Use the same connection when processing the same query.

If the same SELECT statement is executed in different connections, the cache cannot be hit. Therefore, it is recommended to use the same connection when processing the same query to take advantage of the query cache.

4. Avoid using functions or expressions on primary keys.

Using functions or expressions on primary keys will cause query cache misses and may affect performance. It is recommended to use constant queries on primary keys whenever possible.

Conclusion

MySQL query cache is a very useful performance optimization tool that can significantly improve system performance. However, there are certain details to pay attention to when using the query cache, and careful consideration of cache size and system load. We hope that the practical suggestions and methods provided in this article can help you better use the MySQL query cache and improve system performance.

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