Server System Variables SET_VAR  Hint Applies No Type Integer Default Value 256 Minimum Value 256 Maximum Value 524288 Defines a limit for the number of tablespace definition objects, both used and unused, that can be kept in the dictionary object cache. Unused tablespace definition objects are only kept in the dictionary object cache when the number in use is less than the capacity defined by  tablespace_definition_cache . A setting of  0  means that tablespace definition objects are only kept in the dictionary object cache while they are in use. For more information, see Section 14.4, “Dictionary Object Cache” . • temptable_max_mmap • temptable_max_ram 900 Command-Line Format --temptable-max-ram=# System Variable temptable_max_ram Scope Global Dynamic Yes SET_VAR  Hint Applies No Type Integer Default Value 1073741824 Minimum Value 2097152 Command-Line Format --temptable-max-mmap=# Introduced 8.0.23 System Variable temptable_max_mmap Scope Global Dynamic Yes SET_VAR  Hint Applies No Type Integer Default Value 1073741824 Minimum Value 0 Maximum Value 2^64-1 Defines the maximum amount of memory (in bytes) the TempTable storage engine is permitted to allocate from memory-mapped temporary files before it starts storing data to  InnoDB  internal temporary tables on disk. A setting of 0 disables allocation of memory from memory-mapped temporary files. For more information, see Section 8.4.4, “Internal Temporary Table Use in MySQL” .