表倾斜定位与修复

通过查看表数据在各个dn的分布情况判断是否存在数据倾斜

SELECT a.count,b.node_name FROM (SELECT count(*) AS count,xc_node_id FROM table_name GROUP BY xc_node_id) a, pgxc_node b WHERE a.xc_node_id=b.node_id ORDER BY a.count desc;

1. 创建一张新的表，并选取合适的分布列 

   select max(num),min(num) from (select 分布列,count(1) as num from 表 group by 1) a group by 1;

2. 将数据从旧表导入至新表

3. 数据验证

4. rename旧表为bak

5. 将新表重命名为旧表