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## Important 

In MySQL 8.0.16 and later, on-disk internal temporary tables always use the InnoDB  storage engine; as of MySQL 8.0.16, this variable has been removed and is thus no longer supported. 

Prior to MySQL 8.0.16, this variable determines the storage engine used for on-disk internal temporary tables (see Storage Engine for On-Disk Internal Temporary Tables). Permitted values are MYISAM  and INNODB  (the default). 

• internal_tmp_mem_storage_engine 

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The storage engine for in-memory internal temporary tables (see Section 8.4.4, “Internal Temporary Table Use in MySQL” ). Permitted values are TempTable  (the default) and MEMORY . 

The optimizer uses the storage engine defined by internal_tmp_mem_storage_engine  for in- memory internal temporary tables. 

As of MySQL 8.0.26, setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, “System Variable Privileges” . 

• join_buffer_size 

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