I have a table with 45M rows (45 GB data space and 2GB Index space). I added a new column and it finished instantly.
alter table T add C char(25)
Then I found the size is too small so I run the following query.
alter table T alter column C varchar(2500)
And it runs one hour and is still running. sp_whoisactive shows (at the moment, still running)
reads: 48,000,000 writes: 5,000,000 physical reads: 3,900,000
Shouldn't it be really fast?