The ALTER TABLE ALTER CONSTRAINT command acquires AccessExclusiveLock table lock . Following are the locks ALTER TABLE ALTER CONSTRAINT acquires, the commands that are allowed to run concurrently with its lock AccessExclusiveLock and the commands that conflict with it. The list also includes the conflicting row locks if applicable
Commands concurrently allowed on the table with ALTER TABLE ALTER CONSTRAINT
Nothing is allowed to run concurrently with ALTER TABLE ALTER CONSTRAINT
Commands conflicting with ALTER TABLE ALTER CONSTRAINT on the table
e.g. If tx1 does a ALTER TABLE ALTER CONSTRAINT on the table then concurrently tx2 tries to do any of the following commands on the same table, tx2 will be blocked. Conversely, if tx1 executes any of the following commands and then tx2 concurrently tries to execute ALTER TABLE ALTER CONSTRAINT, tx2 will block.