How to Diagnose and Optimize MySQL Table Cache Using Open Tables Metrics
This guide explains the meaning of MySQL's Open_tables and Opened_tables status variables, shows how to check them, and provides recommended ratios and steps to adjust the table_cache setting for better database performance.
In MySQL, Open_tables shows the number of tables currently opened, while Opened_tables counts the total tables opened since the server started.
You can view these values with:
show global status like 'open%tables%';If Opened_tables is high, the table_cache setting may be too low. Check the current cache size:
show variables like 'table_cache';Typical healthy ratios are:
Open_tables / Opened_tables × 100 ≥ 85 %
Open_tables / table_cache × 100 ≤ 95 %
Adjust the cache size accordingly, for example: SET GLOBAL table_cache=600; After changing the value, monitor the ratios again to ensure optimal performance.
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