Question

We are using SQL Server 2008. We have an Existing database and it was required to ADD a new COLUMN to one of the Table which has 2700 rows only but one of its column is of type VARCHAR(8000). When i try to add new column (CHAR(1) NULL) by using ALTER table command, it takes too much time!! it took 5 minutes and the command was still running to i stopped the command.
Below is the command, i was trying to add new column:

ALTER TABLE myTable Add ColumnName CHAR(1) NULL

1. Can someone help me to understand that How the SQL Server handles
   the ALTER Table command? what happens exactly?
2. Why it takes so much time to Add new column

EDIT:

1. What is the effect of Table size on ALTER Command?

Answer 1

Altering a table requires a schema lock. Many other operations require the same lock too. After all, it wouldn’t make sense to add a column halfway a select statement.

So a likely explanation is that a process had the table locked for 5 minutes. The ALTER then has to wait until it gets the lock itself.

You can see blocked processes, and the blocking process, from the Activity Monitor in SQL Server Management Studio.