MariaDB Performance Optimization: Tuning the Table Open Cache in 10.3.13

Table Open Cache:

• In MariaDB, the table_open_cache stores recently opened tables in memory.
• When an application needs to access a table, MariaDB checks the cache first.
• If the table is in the cache, it's faster to access than reading it from disk.

The Problem in MariaDB 10.3.13:

• In older versions of MariaDB (like 5.6.7), the default value for table_open_cache was 400.
• MariaDB 10.3.13 increased the default value to 2000.

This change might cause issues for some setups:

• If your system doesn't have enough memory to hold 2000 tables, MariaDB performance can suffer.
• Applications might see issues like slow queries or errors if they can't open the tables they need.

Solutions:

• Check your MariaDB configuration and adjust the table_open_cache value if needed.
• A lower value (closer to 400) might be better if your system has limited memory.
• Monitor MariaDB performance to see if the cache size is causing problems.

Additional Notes:

• There's no one-size-fits-all solution for table_open_cache. The optimal value depends on your specific workload and system resources.
• If you're unsure about the best value, consult the MariaDB documentation or seek help from a database administrator.

Check Current Value:

You can check the current table_open_cache value using a MariaDB client like mysql. Here's an example:

mysql> SHOW GLOBAL VARIABLES LIKE 'table_open_cache';
+-----------------+-------+
| Variable_name    | Value |
+-----------------+-------+
| table_open_cache | 2000  |  // This might be different on your system
+-----------------+-------+

Adjust the Value (if needed):

You can modify the table_open_cache value in the MariaDB configuration file (usually named my.cnf). Here's an example:

[mysqld]
# Other configuration options...

table_open_cache = 1000  // Adjust this value as needed

1. Dynamically adjust the cache size:

• MariaDB offers dynamic table cache management through internal algorithms. You can enable this by setting the table_open_cache_instances variable in my.cnf. This allows MariaDB to automatically adjust the cache size based on workload.

1. Monitor and fine-tune:

   • Use monitoring tools to track the table_open_cache hit rate (percentage of times tables are found in the cache). An ideal hit rate is between 80% and 90%. If it's consistently lower, increase the cache size. Conversely, if it's frequently above 90%, you might be able to reduce the cache size to free up memory for other applications.

2. Utilize query optimization:

   • Optimizing queries can reduce the need for frequent table access, indirectly affecting the table_open_cache. Techniques like proper indexing and avoiding redundant joins can help.

3. Consider alternative storage engines:

   • If your workload involves frequently changing data or a high number of small tables, explore alternative storage engines like Memory engine (memory-resident tables) or InnoDB with smaller cache settings. These might be better suited for specific use cases.