How to Clear MySQL Cache: Best Practices for Version-Specific Cache Types

1. Introduction

MySQL is a representative database used by many web services and systems worldwide. In order to improve performance and reduce server load, MySQL provides various caching mechanisms. However, in development or operational environments, you may encounter issues such as “latest data not reflected due to cache” or “old cache gets in the way when changing settings or debugging”.

In such scenarios the operation of “clearing (deleting or resetting) MySQL’s cache” becomes useful. For example, when you want to instantly confirm data updates in a test environment, clear all caches before taking a snapshot, or forcefully reset unintended remaining cache, this operation is highly effective.

In this article, we will explain in a clear manner for those interested in “mysql cache clear” by type of cache, how to clear each cache type. We will also cover differences in cache specifications by MySQL version, operational cautions, and frequent questions and their solutions.

By fully understanding the mechanism of cache and the clearing methods, you should be able to use MySQL more stably and efficiently.

2. Cache Architecture by MySQL Version

MySQL’s caching functions differ significantly in content and behavior depending on the version. Especially between MySQL 5.7 and earlier and MySQL 8.0 and later, the design philosophy of caching itself has changed. Here we organize the main types of caches commonly used in MySQL and the differences by version.

2.1 Query Cache (MySQL 5.7 and Earlier)

In versions of MySQL prior to 5.7, a function called “Query Cache” was standard. This mechanism stores executed SELECT statements and their result sets in memory, and when the same query arrives it returns the result quickly. It is effective for simple web services, but in environments with many data updates, the cache is frequently invalidated and can instead cause performance degradation.

2.2 InnoDB Buffer Pool (MySQL 5.5 onwards → 8.0)

From MySQL 5.5 onward, and particularly in MySQL 8.0, the “InnoDB Buffer Pool” has become the core caching function. This mechanism allows the InnoDB storage engine to keep data and index information in memory, reducing disk I/O and accelerating performance. Unlike the query cache, the buffer pool caches table-wide or row-level data, so stable performance can be expected even in large systems or systems with frequent updates.

2.3 Table Cache and Other Caches

In addition, MySQL has multiple caches such as “table cache (table_open_cache)”, “thread cache”, “user-variable cache”. In particular, the “table cache” plays a role in efficiently managing frequently accessed tables, and it is used across all versions.

2.4 Summary of Cache Specifications by Version

• MySQL 5.7 and earlier: Query Cache + InnoDB Buffer + Table Cache
• MySQL 8.0 and later: Query Cache discontinued, InnoDB Buffer Pool as main, Table Cache continues

Thus, because the types and roles of cache change depending on MySQL version, it is important to know the appropriate measures for the version you are using.

3. How to Clear the Query Cache (for MySQL 5.7 and Earlier)

If you are using MySQL 5.7 or earlier, the “Query Cache” feature is often enabled. In this section we explain in detail the mechanism of the query cache, methods to clear it, and precautions.

3.1 What is Query Cache?

Query Cache stores SELECT statements and their result sets in memory and returns results instantly when the same query is executed again. It is effective for websites that refer to a lot of static data or small-scale applications, but in environments with high data update frequency the usefulness of the cache drops, so caution is needed.

3.2 Commands to Clear Query Cache

To clear the query cache the following two commands are mainly used.

• RESET QUERY CACHE;
  Deletes all entries in the query cache. If you want to completely eliminate the influence of cache, this is effective.
• FLUSH QUERY CACHE;
  Deletes only entries in the cache that are “unused”. Suitable when you want to clean up only old entries that have already been invalidated.

3.3 How to Execute the Commands

From the MySQL client or management tool (such as phpMyAdmin), execute the commands as follows:

RESET QUERY CACHE;

Or

FLUSH QUERY CACHE;

Administrator privileges may be required, so if you get a permission error execute again with administrator privileges (such as root).

3.4 Precautions and Best Practices

• Clearing the query cache affects the entire server, so perform with caution in production environments.
• When cache is cleared, performance may temporarily degrade.
• In MySQL 8.0 and later the query cache function itself has been abolished, so these commands cannot be used.

By effectively clearing the query cache you can prevent unintended cache effects, enable latest data reflection and accurate behavior verification.

4. Clearing Table Cache and Related Caches

MySQL has various caching functions other than query cache. Especially “table cache” is used to efficiently manage tables that are frequently accessed. This chapter explains how to clear table cache and related caches.

4.1 What is Table Cache?

Table cache (table_open_cache) is a mechanism by which MySQL keeps tables open internally and avoids the overhead of reading from disk each time access occurs. It improves performance when there are many concurrent accesses from multiple users or applications.

4.2 How to Clear Table Cache

To clear the table cache, you mainly use the FLUSH TABLES command.

FLUSH TABLES;

Executing this command closes all open tables, and when needed they will be reopened. This resets the table cache content, thus helping when table definitions change or cache-related issues arise.

4.3 Clearing Other Related Caches

In MySQL, commands for clearing various caches other than table cache are provided. For example:

• FLUSH TABLES WITH READ LOCK;
  Closes all tables and locks them for use in backups, etc.
• FLUSH PRIVILEGES;
  Clears user/privilege information cache to immediately reflect privilege changes.
• FLUSH STATUS;
  Resets statistical information of various status variables (viewable via SHOW STATUS, etc.).

4.4 Clearing Multiple Caches Together

Since the clearing commands differ by cache type, if you want to reset multiple caches together, execute each command in sequence. For example, in a development or test environment where you want to “reset all caches at once”:

FLUSH TABLES;
RESET QUERY CACHE;

Use this kind of combination (※ Note: in MySQL 8.0 or later RESET QUERY CACHE cannot be used).

4.5 Precautions

• Clearing the table cache may temporarily impact performance in systems with many open tables.
• For production environments execute only after checking the scope of influence.
• Some commands may not execute depending on privileges. If errors appear, re-execute as a user with appropriate privileges.

By properly clearing table cache and related caches you can make MySQL’s stable operation and troubleshooting easier.

5. How to “Clear” the InnoDB Buffer Pool (for MySQL 8.0 and Later)

From MySQL 8.0 onward the query cache feature has been removed, and the InnoDB Buffer Pool assumes the central role for caching. However, unlike the query cache, the InnoDB Buffer Pool cannot be “cleared” with a single command. This chapter explains approaches and precautions for effectively clearing or resetting the InnoDB Buffer Pool.

5.1 What is the InnoDB Buffer Pool?

The InnoDB Buffer Pool caches table data, indexes, and frequently accessed data pages in memory, reducing disk I/O and enabling faster performance. In MySQL 8.0 this buffer pool is a key performance component.

5.2 Methods and Alternatives for Buffer Pool Clear

The InnoDB Buffer Pool does not provide a standard command to directly “clear” it. The main methods are as follows:

• MySQL server restart
  By stopping and restarting the server you effectively initialize the buffer pool contents, achieving a full clear. However, in production environments this requires careful operation.
• Temporarily changing the buffer-pool size
  By reducing the innodb_buffer_pool_size setting, restarting MySQL, then returning it to its original value and restarting again, you can also initialize the buffer pool.
• Flushing individual buffer-pool pages
  With the following command you can write out changed pages (dirty pages) from the buffer pool to disk, but this does not fully clear the cache itself.

  FLUSH TABLES;

5.3 Example of Buffer Pool Clear in Practice

For example, when you want to clear the buffer pool in a test environment, carry out the following steps:

1. Stop the MySQL server
2. Adjust innodb_buffer_pool_size (if required)
3. Start the MySQL server

This resets the memory buffer pool and results in a state where all cache information is removed.

5.4 Precautions and Operational Tips

• Initializing the buffer pool (via server restart) results in temporary service downtime. In production environments advanced planning and announcements are essential.
• Immediately after clearing the buffer pool, disk access increases and performance may temporarily degrade. Be especially careful in high-traffic systems.
• If restart is impossible, prepare a separate test or development environment and carry out verification work there safely.

By thoroughly understanding the operation of the InnoDB Buffer Pool and executing clear or reset operations at proper timing, you can achieve stable operations even in MySQL 8.0 and later environments.

6. Cache Control with Third-Party Tools

Cache management in MySQL becomes more efficient and visible not only with standard commands but also by using various third-party tools or utilities. Here we introduce representative tools and usage examples.

6.1 Cache Monitoring and Optimization with MySQLTuner

“MySQLTuner” is a well-known diagnostic tool that analyzes the status of a MySQL server and automatically provides advice for performance improvement. It also presents usage status of caches (query cache, InnoDB buffer pool, table cache etc.) and gives suggestions for optimal settings.

Usage steps for MySQLTuner:

1. Install MySQLTuner on the server (distributed as a Perl script).
2. Execute the following command for diagnosis.

   perl mysqltuner.pl

3. The execution result displays diagnostic items such as “Query cache” and “InnoDB Buffer Pool”, and provides recommendations on parameter adjustments or disabling unnecessary cache features.

6.2 Utilization of Percona Toolkit

“Percona Toolkit” is a suite of tools useful for MySQL operation and performance analysis. For example it can generate reports with a single command on the status of the buffer pool or table cache usage, making it convenient for understanding situations in large-scale operations.

6.3 Examples of Monitoring / Visualization Tools

• phpMyAdmin · MySQL Workbench
  These management tools also enable you to view current cache states and execute some FLUSH commands from a GUI. They are user-friendly for beginners and suited for status monitoring or minor cache control.
• Zabbix or Prometheus
  You can visualize in real time memory usage of servers or InnoDB buffer pool usage, monitor cache behavior and resource pressure, detect anomalies early, and set up automatic alerts.

6.4 Precautions When Using Third-Party Tools

• Tool execution may require administrator privileges or specific MySQL user privileges.
• Using tools in production environment is recommended only after testing in a staging environment.
• Some tools may increase server load temporarily, so consider executing during off-peak or low-usage hours.

By skillfully leveraging third-party tools you can visualize the cache state of MySQL and perform clear or optimization operations at the right timing.

7. Risks and Precautions

Clearing MySQL cache is very useful but if done at the wrong time or in the wrong way, it can lead to unexpected troubles or performance degradation. In this chapter we explain the risks and precautions you must know when executing cache clear.

7.1 Impact on Performance

Clearing cache may cause server load to spike after the operation. Especially when large caches like the InnoDB buffer pool or table cache are cleared, all data in memory is lost, so disk I/O will occur for each request which may significantly slow response times.

7.2 Exercise Caution in Production Environments

When performing cache clear on a system that is under live production use, care is particularly needed. Executing during high-traffic hours may impact the entire system performance, causing service disruption or response delays. In production you must perform adequate testing, preparation, and consider timing and backups ahead of time.

7.3 Consideration for Data Updates and Integrity

The timing of cache clear can result in unexpected application behavior or data inconsistencies. For example, if you clear cache during table structure changes or during batch processing, query results or application logic may behave unexpectedly.

7.4 Avoid Unnecessary Cache Clears

An operation mindset of “let’s clear cache anyway” should be avoided. MySQL cache is originally designed to reduce server load and speed up processing. Frequent clears may instead result in performance instability. Focus on “clear only when necessary”.

7.5 Privilege and Security Considerations

The commands or tool usage to clear cache require sufficient privileges. Running as a user with full privileges without caution can impact other important settings or data, so you should work with the minimum-privilege user, record execution history, and consider security as well.

By understanding these risks and precautions you will be able to carry out cache clear operations safely and efficiently, thereby maintaining MySQL’s stable performance and smooth operation.

8. Procedure Summary (Quick Reference Table)

Here we summarise the MySQL cache clear procedures introduced so far by cache type and version in a quick reference table. This helps you quickly identify commands and purposes for actual operation or troubleshooting.

Quick Explanation:

• RESET QUERY CACHE;
  Reset all query cache (MySQL 5.7 and earlier only).
• FLUSH QUERY CACHE;
  Delete only invalidated unused query cache.
• FLUSH TABLES;
  Close all open tables once and reset table cache.
• FLUSH PRIVILEGES;
  Use when you want to immediately reflect user-privilege changes.
• FLUSH STATUS;
  Reset various status statistics. Useful for performance analysis.
• Initializing InnoDB Buffer Pool
  Indirectly achieved by server restart or changing innodb_buffer_pool_size (MySQL 8.0 and later).

By using this table you can quickly decide the correct cache clear procedure according to version and purpose in your environment.

9. FAQ (Frequently Asked Questions)

Here we compile questions frequently asked by field engineers and operators about MySQL cache clearing, along with their answers. Use this as reference during actual operation.

Q1. Are the Query Cache and InnoDB Buffer Pool the same?

A. No, they are different mechanisms. Query Cache stores result sets of SQL queries, while the InnoDB Buffer Pool holds table data, indexes and so on in memory. Because their usage and mechanisms are entirely different they should not be confused.

Q2. How much does performance drop after clearing the cache?

A. Performance temporarily declines. Particularly in environments with large caches, disk access increases on the first query execution and response time may fall significantly. However, performance recovers gradually as the cache is rebuilt.

Q3. Is it safe to clear cache in a production environment?

A. It is not generally recommended. Clearing cache in production can directly impact performance and service stability, so adequate testing, preparation, and timing adjustment are essential. If you must carry it out, don’t forget to announce and backup before execution.

Q4. Can I enable Query Cache in MySQL 8.0?

A. No. In MySQL 8.0 the Query Cache feature was completely removed. If you want to use Query Cache you must use MySQL 5.7 or earlier.

Q5. Can you clear cache in cloud services like AWS RDS or Cloud SQL?

A. It is possible, but commands or operation privileges available differ by service. For example, in RDS some FLUSH commands or server restart operations may be restricted, so check official documentation or management console guidelines when working.

Q6. Is there a way to automatically clear cache?

A. It is possible to use shell scripts or cron jobs to periodically execute FLUSH commands. However, frequent cache clearing is not recommended. Use it only at necessary timing or during maintenance.

Referring to this FAQ allows you to address concerns or doubts in the field ahead of time and make MySQL cache clear operations more reliable.

10. Conclusion and Best Practices

Clearing MySQL cache is an essential operation in development or production environments. In this article we covered cache types by MySQL version, methods to clear, precautions, and frequently asked questions. Finally, we summarise best practices.

10.1 Actively use cache clear in test environments

When performing tests, verification or debugging you often want to remove cache influence and confirm “actual behavior”. Use cache clear commands as needed to increase reproducibility and accuracy of behavior confirmation.

10.2 Use cautious operation in production environments

Clearing cache in production environments can have large impact on service performance and stability. Before execution always evaluate the scope of impact, timing, notify stakeholders and perform backup. Avoid simply clearing cache indiscriminately; focus on “execute only when really necessary”.

10.3 Understand versions and cache types correctly

MySQL’s caching functions vary by version, so it is important to accurately grasp which caches and clearing methods apply to your environment. Also, since commands and impact differ by cache type, select the optimal procedure depending on use case.

10.4 Leverage third-party tools and monitoring tools

Tools such as MySQLTuner or Percona Toolkit allow objective evaluation of server status and cache usage rates. Utilize visualization and automation to support advanced operations and preventive troubleshooting.

10.5 Summary

If you carry out MySQL cache clearing appropriately, it will greatly support stable operation, troubleshooting and performance improvement of your database. Use this article as reference, apply methods suitable for your environment and usage, and aim for higher-quality system operations.