mysql 8.x 如何开启have_query_cache

MySQL 8.x 中已经废弃了查询缓存（Query Cache）功能，因此没有`have_query_cache`参数。如果需要使用缓存功能，可以考虑使用内存表（Memory Engine）和临时表（Temporary Table）的缓存功能。

如果您仍然希望开启查询缓存功能，可以使用以下步骤：

1. 编辑MySQL配置文件`my.cnf`，添加以下参数：

   query_cache_type=1
   query_cache_size=64M
   query_cache_limit=1M

`query_cache_type`参数设置为1，表示启用查询缓存功能。`query_cache_size`参数设置为缓存的最大值，`query_cache_limit`参数设置为单个查询的最大缓存大小。

2. 重启MySQL服务。

需要注意的是，查询缓存功能在MySQL 8.x中已经被废弃，因为它可能会导致性能问题。如果您需要启用缓存功能，建议使用内存表和临时表的缓存功能，或者使用其他缓存方案来优化查询性能。

相关问题

reset query cache

As an AI language model, I don't have the capability to reset the query cache. However, here's how you can reset the query cache in MySQL:

To reset the query cache in MySQL, you can use the following command:

RESET QUERY CACHE;

This command clears the query cache and removes all the cached queries from memory. After running this command, MySQL starts caching new queries.

Note that resetting the query cache can affect the performance of your MySQL server temporarily. Therefore, it's recommended to reset the query cache during off-peak hours when the server load is low.

mysql redis mongodb

MySQL, Redis, and MongoDB are all popular database management systems, but they have different characteristics and are suited for different use cases.

MySQL is a relational database management system that uses SQL (Structured Query Language) for querying and managing data. It is a popular choice for web applications, e-commerce sites, and other data-heavy applications that require the ability to scale and manage large amounts of data.

Redis is an in-memory data structure store that can be used as a database, cache, and message broker. It is optimized for high-performance data storage and retrieval, making it a good choice for real-time applications, such as gaming, messaging, and social media.

MongoDB is a NoSQL document-oriented database that uses JSON-like documents for storing data. It is designed to be scalable and flexible, making it a good choice for applications that require a high degree of flexibility in their data models, such as content management systems, mobile apps, and IoT applications.

Ultimately, the choice between these database management systems will depend on the specific requirements of your application and the characteristics of your data.