How to change join_buffer_size in MySQL

I will give an example of changing join_buffer_size in MySQL.
join_buffer_size determines the size of the buffer for index scanning and joins without indexes. I recommend adding indexes or slightly increasing join_buffer_size (but in this case a full table scan will be performed).

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Recovering MySQL InnoDB after power failure

Once, after the power was turned off, the UPS was discharged, then the generator automatic start did not work because it turned on and off several times, as a result, the server with MySQL was also started and disconnected from the power supply several times, later the tables of different databases were damaged , including the default database with mysql users, as a result, the MySQL daemon did not start.

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