Contents
What is table definition cache?
Table Definition Cache. This parameter shows the number of table definitions (SHOW CREATE TABLE \G) that can be stored. This is to speed up opening of tables and only one entry per table. You should consider increasing this parameter if you have large number of tables (>400) in your DB instance.
What is MySQL table definition cache?
MySQL also requires memory for the table definition cache. The table_definition_cache system variable defines the number of table definitions that can be stored in the table definition cache. If you use a large number of tables, you can create a large table definition cache to speed up the opening of tables.
What is MySQL Opened_tables?
Opened_tables is a status variable that keeps a running tally of the number of additional file descriptors that have been allocated for opening tables at times when the available file descriptors in table_cache have been depleted. Meaning that it is incremented when you go over your table_cache value.
How do I set table definition cache in MySQL?
mysql> show global status like ‘open%’; The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable.
What should mysql table definition cache be set to?
So I set the table_definition_cache = 512M, just to be safe, but it got readjusted on the startup to max value of “524288”. Which is not really enough for my Database.
How big should table open cache instances be?
Calculating table_definition_cache: Setting up table_open_cache_instances: A value of 8 or 16 is recommended on systems that routinely use 16 or more cores, the default is 1. table_open_cache_instances – Should be bigger than 1; up to the number of CPU cores.
How to tune / calculate table open cache, open _ files _ limit?
Along with table_open_cache you should also tune open_files_limit system variable. In general its double of table_open_cache. Calculating table_definition_cache: Setting up table_open_cache_instances: A value of 8 or 16 is recommended on systems that routinely use 16 or more cores, the default is 1.