What is shared lock and deadlock in SQL?

When a transaction is going to modify data, a Shared lock is used to read the data. After that, an Exclusive lock is placed to modify that data. When two transactions are waiting on each other to convert Shared locks on resources to Exclusive locks, a deadlock occurs.

What no lock does in SQL?

The WITH (NOLOCK) table hint is used to override the default transaction isolation level of the table or the tables within the view in a specific query, by allowing the user to retrieve the data without being affected by the locks, on the requested data, due to another process that is changing it.

Does serializable lock table?

SERIALIZABLE – lock on a full table(on which Select query is fired). This means, B reads the data and no other transaction can modify the data on the table. This is the most secure but slowest way to work with data.

What is the difference between updlock and holdlock in SQL?

UPDLOCK makes the locks to be taken and held until the transaction completes. HOLDLOCK only applies for the duration of the statement it is applied on, so it makes sense to combine it with UPDLOCK to extend it for the duration of the whole transaction. ROWLOCK forces the locks to be taken only on rows, without escalating to Page or Table.

When to use the updlock hint to avoid deadlocks?

Thus, if a transaction reads data which potentially can be updated in that transaction, and there are concurrent transactions that can try to change the same data, the UPDLOCK hint can be used while reading this data in order to avoid deadlocks. Now, let’s test this behavior in practice.

What is the difference between updlock and update lock?

When the data is updated, the lock will be freed UPDLOCK uses an update lock when reading a table instead of a shared lock, and keeps the lock until the end of the statement or transaction.