PostgreSQL on QingCloud 正式支持列存储，查询性能提升 35 倍！

### 性能数据
- Count(*)
  35倍性能提升
  ```  -- 列存用时 4秒  postgres=# select count(*) from perf_columnar ;    count     ----------   75000000  (1 row)    Time: 4369.697 ms (00:04.370)    -- 行存用时 137秒  postgres=# select count(*) from perf_row ;    count     ----------   75000000  (1 row)    Time: 137164.623 ms (02:17.165)  ```
- 分析性能
  11倍性能提升
  ```  -- 行存用时 134秒  postgres=# SELECT vendor_id, SUM(quantity) FROM perf_row GROUP BY vendor_id OFFSET 1000;   vendor_id | sum   -----------+-----  (0 rows)  Time: 134067.674 ms (02:14.068)    -- 列存用时 14秒  postgres=# SELECT vendor_id, SUM(quantity) FROM perf_columnar GROUP BY vendor_id OFFSET 1000;   vendor_id | sum   -----------+-----  (0 rows)  Time: 14184.814 ms (00:14.185)    ```