I've seen lots of information around adding a new primary key column to a large database table, but I have a somewhat different situation.
I have a large table (~90,000,000 records), that has no primary key. However, it DOES have a "RowID" column, which is an identity column. It also has a unique index on the RowID column.
All my research showed that a table without a primary key is terrible design that should be gotten rid of if at all possible. In my particular case; it's causing issues because Entity Framework maps the table as a read only view if it can't find a primary key.
I want to add a primary key constraint to the table on the RowID column. I was hoping that because it's not adding a new column, and there's already a unique index on that column, that it would be a small operation; however, it appears from a test run that it will take a very long time.
Having this table be inaccessible for a long time will cause issues across our business. I know that another option is to create a new table with the new schema, and copy all data from the old to the new. But this will also cause us to need to lock down the table for a long time.
Is there a way to more quickly add the primary key constraint when you already have an identity column with a unique index?