How to use caching technology in MySQL to improve query speed?

How to use caching technology in MySQL to improve query speed?

Caching is a common performance optimization technology. By storing frequently accessed data in memory, it can reduce query operations on the database, thereby increasing query speed. In MySQL, we can use a variety of methods to implement caching, including using query cache, application-level cache, etc. This article will take MySQL's query cache as an example to introduce how to use caching technology in MySQL to improve query speed.

1. Configuring query cache
   The query cache function of MySQL is turned off by default, and we need to make relevant settings in the configuration file. Open the MySQL configuration file (my.cnf) and find the following section:

[mysqld]
query_cache_type = 1
query_cache_size = 64M
query_cache_limit = 2M

Set query_cache_type to 1 to enable query caching. query_cache_size sets the cache size and adjusts it according to the actual situation. query_cache_limit limits the maximum value that a single query result can be cached, and can also be configured as needed.

After the configuration is completed, restart the MySQL service.

2. Use of Query Cache
   In MySQL, only query statements that meet the following conditions will be cached:

• Sensitivity is not used in the query statement words, such as NOW(), RAND(), etc.
• The result set of the query statement has not changed.
• The query statement uses the same parameters.

We can use the following command to view the usage of the query cache:

SHOW VARIABLES LIKE 'query_cache%';

If query_cache_hits is 0, it means that the query cache is not used.

3. Cache Invalidation
   The disadvantage of query caching is that when the data changes, the cache will not automatically expire. In order to avoid reading dirty data, we need to manually invalidate the cache when the related table is modified.

FLUSH QUERY CACHE;

By executing the above command, you can clear the query cache and make it invalid.

4. Optimize query
   In order to maximize the use of the query cache, we need to optimize the query statement to improve the cache hit rate. The following are some ways to optimize queries:

• Try to avoid using sensitive words, such as NOW(), RAND() and other functions, so that query statements can be cached.
• Avoid using dynamic parameters, such as time, random numbers, etc. as query conditions.
• For tables that are frequently updated, you can consider canceling cached queries or reducing the cache time.

5. Tuning the cache size
   The size of the query cache is a parameter that needs to be continuously tuned. If the cache is too small, the query cache hit rate may be low, and the cache cannot improve the query speed; if the cache is too large, it will occupy too many memory resources, causing MySQL's performance to decline. Depending on the actual situation, tuning can be performed by monitoring the query cache hit rate and occupied memory size.

Summary:
By properly configuring the query cache, using caching technology in MySQL can significantly improve query speed. However, it should be noted that query caching is not suitable for all types of scenarios. Especially for tables that are frequently updated, the caching effect may be poor and even affect the performance of MySQL. Therefore, while using caching technology, comprehensive performance tuning is also required to achieve the best query performance.

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