mysql query cache

MySQL is a relational database management system and one of the most commonly used databases in web applications. In MySQL, query caching is a key feature that can greatly improve the performance and response speed of the database. This article will introduce in detail how the MySQL query cache works and how to optimize the use of the query cache.

1. Working principle of MySQL query cache

MySQL query cache is an internal cache used to store the mapping relationship between query results and query statements. When a query is executed, MySQL will first check whether the same query statement and query results have been stored. If it already exists, it will directly return the query results to avoid executing the query statement and accessing the database again.

The mapping relationship saved in the query cache consists of two parts: query statements and query results. In order to ensure the consistency and correctness of the cache, MySQL will automatically delete the relevant query cache after any update operation (insert, update, delete). This also means that in a database that is updated frequently, the query cache hit rate will be very low.

2. Optimization of MySQL query cache

1. Enable query cache

By default, MySQL will enable query cache. In the configuration file, the query cache parameter is set to the default value "ON". If you need to confirm whether the query cache is turned on, you can query it with the following statement:

SHOW VARIABLES LIKE 'query_cache_type';

If the query result is "ON", it means that the query cache is turned on. If the query result is "OFF", you need to manually enable query caching.

2. Set the size of the query cache

The default size of the MySQL query cache is 8MB. If the cache size is too small, the cache will be cleared and rebuilt frequently under high concurrency conditions, thus reducing the efficiency of the query cache. You can set the size of the query cache through the following statement:

query_cache_size=1048576;

where 1048576 represents the cache size in bytes.

3. Cache cacheable queries

The query cache can only cache SELECT statements and non-locked tables. If the query is complex or the query contains statements with dynamic functions such as NOW() or RAND(), the cache may not be available. Therefore, when using query cache, you need to pay attention to the writing and optimization of SQL statements.

4. Avoid update operations

Since the MySQL query cache will automatically delete the relevant query cache after the update operation, avoiding frequent update operations can improve the effectiveness of the query cache. sex. In practical applications, you can consider using mechanisms such as cache updates to avoid frequent update operations.

5. Partitioned table

MySQL query cache can only cache non-locked tables. If the table is updated, the query cache becomes invalid. To get the most out of your query cache, consider splitting your table into multiple regions, each of which can be updated independently. This way, even if one region is updated, the query cache for other regions can still be cached and used.

6. Avoid memory bottlenecks

Query caching is done in memory, so if the MySQL server has small memory and multiple queries are running at the same time, a memory bottleneck may occur , thus affecting the operation of the query cache. To avoid this situation, the server's memory usage needs to be monitored regularly and the server's memory adjusted as needed.

3. Conclusion

MySQL query cache is a very useful feature that can significantly improve database performance and response speed. However, you need to pay attention to the following points when using the query cache: ensure that the query cache is turned on; adjust the size of the query cache; cache cacheable queries; avoid frequent update operations; partition the table; and avoid memory bottlenecks. By optimizing the MySQL query cache, we can maximize the advantages of the query cache and improve the performance and response speed of the database.

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