posted 10 years ago
Are you sure the update is locking it? Have you used some database tools to identify the offending transaction/statement? There could be some other, overlooked process that is locking the table (eg. deleting a row from a parent table might lock the child table if it doesn't have its foreign key indexed).
Assuming it is the update operation, it might be caused by lock escalation. The details of locking are database dependent. Some databases don't ever escalate locks, while others do, under different conditions. I'd suggest to consult your database documentation to find out why, when and how a lock escalation can occur.