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[ERROR] /usr/local/libexec/mysqld: unknown variable ‘thread_concurrency=8’

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The error message you are seeing indicates that the MySQL server is not able to recognize the "thread_concurrency" variable that is set to a value of 8 in the configuration file. The "thread_concurrency" variable was used in older versions of MySQL to control the number of threads that are used to process queries.

To resolve the error, you can do the following:

  1. Check the version of MySQL that you are running. The "thread_concurrency" variable was deprecated in MySQL 5.5 and removed in MySQL 5.7. If you are running a version of MySQL that is 5.7 or later, you can remove the "thread_concurrency" variable from your configuration file.
  2. If you are running an older version of MySQL that still supports the "thread_concurrency" variable, you can try changing the variable name to "thread_concurrency_level". This variable was introduced in MySQL 5.5 as a replacement for "thread_concurrency".
  3. Alternatively, you can try commenting out the "thread_concurrency" line in your configuration file by adding a "#" character at the beginning of the line. This will disable the variable and allow MySQL to start without throwing an error.
rnOnce you have made the necessary changes to your configuration file, restart the MySQL server to apply the changes.

Note that if you are using a version of MySQL that is 5.7 or later, it is recommended to use the "innodb_thread_concurrency" variable instead of "thread_concurrency" to control the number of threads used for InnoDB operations.