为什么在mysql中重命名一个列需要这么长时间?

I have a 12 GB table full of pictures, I'm trying to rename the blob column that holds the data, and it is taking forever. Can someone give me a blow by blow account of why it is taking so long to rename the column? I would have thought that this operation would be pretty quick, no matter the size of the table?I have a 12 GB table full of pictures, I'm tryi