Describe the bug
When query two columns in a wide table (table1) which has many columns, in this case is 178 columns.
I found that BlockConvertTime in query profile takes majority of query time. The information is like following picture.

But when I create a new table (table2) which has only 5 columns and has the same number of rows with table1. And a same query is executed for table2, BlockConvertTime becomes extremely low.

So, there is some space which can be improved when Doris handle wide table.