InnoDB System Variables Defines the location where  InnoDB  creates a pool of session temporary tablespaces at startup. The default location is the  #innodb_temp  directory in the data directory. A fully qualified path or path relative to the data directory is permitted. As of MySQL 8.0.16, session temporary tablespaces always store user-created temporary tables and internal temporary tables created by the optimizer using  InnoDB . (Previously, the on-disk storage engine for internal temporary tables was determined by the  internal_tmp_disk_storage_engine  system variable, which is no longer supported. See Storage Engine for On-Disk Internal Temporary Tables.) For more information, see Session Temporary Tablespaces. Defines the maximum number of threads permitted inside of  InnoDB . A value of 0 (the default) is interpreted as infinite concurrency (no limit). This variable is intended for performance tuning on high concurrency systems. InnoDB  tries to keep the number of threads inside  InnoDB  less than or equal to the innodb_thread_concurrency  limit. Once the limit is reached, additional threads are placed into a “First In, First Out”  (FIFO) queue for waiting threads. Threads waiting for locks are not counted in the number of concurrently executing threads. The correct setting depends on workload and computing environment. Consider setting this variable if your MySQL instance shares CPU resources with other applications or if your workload or number of concurrent users is growing. Test a range of values to determine the setting that provides the best performance.  innodb_thread_concurrency  is a dynamic variable, which permits experimenting with different settings on a live test system. If a particular setting performs poorly, you can quickly set innodb_thread_concurrency  back to 0. Use the following guidelines to help find and maintain an appropriate setting: 3291 •If the number of concurrent user threads for a workload is consistently small and does not affect performance, set  innodb_thread_concurrency=0  (no limit). •If your workload is consistently heavy or occasionally spikes, set an  innodb_thread_concurrency value and adjust it until you find the number of threads that provides the best performance. For example, suppose that your system typically has 40 to 50 users, but periodically the number increases • innodb_thread_concurrency Type Directory name Default Value #innodb_temp Command-Line Format --innodb-thread-concurrency=# System Variable innodb_thread_concurrency Scope Global Dynamic Yes SET_VAR  Hint Applies No Type Integer Default Value 0 Minimum Value 0 Maximum Value 1000