show variables like 'max_%';
| max_heap_table_size | 16777216 |
| max_tmp_tables | 32 |
show variables like 'tmp_%';
| tmp_table_size | 1048576000 |
set tmp_table_size=1048576000
set max_heap_table_size=10240000000;
需要重启mysql服务才生效
set global read_buffer_size = 10240000;