查看所有的参数
show variables like "%%";
查看cbo_enable_low_cardinality的参数
show variables like "%cbo_enable_low_cardinality%";
参数设置
set global cbo_enable_low_cardinality_optimize = false
pipeline引擎，资源利用率高
set global enable_pipeline_engine = false;
设置并行度
set global parallel_fragment_exec_instance_num = 8;