When performing joins, if they are below this size, they will be kept in memory and never written to a temporary file.As this is a per connection memory allocation, care must be taken not to increase it too high.The sum of the join_buffer_size + sort_buffer_size + read_buffer_size + read_rnd_buffer_size + thread_stack + binlog_cache_size + Core MySQL/MariaDB memory should be below 80%.If the recommendation is negative, you must decrease this and or the sort_buffer_size until the recommendation fits within the allowable memory.