ReadUncommitted

Reads all data, regardless of whether it has been committed to the database. This means that the query can read data from table rows that have been modified by another running transaction, but have not yet been committed.

This mode is sometimes referred to as a dirty read. For those familiar with SQL, this translates to reading the data with ‘Read Uncommitted’.

No additional locks are placed on the read data. Because the query does not lock the rows it reads, other transactions can also read, modify, and delete the same data as the query.

Setting the property to ReadUncommitted can improve performance compared to ReadShared and ReadExclusive. However, the query can read data that potentially is rolled back or changed by another transaction when the query is running.

ReadShared

Reads only data that has been committed to the database.

Share locks are placed on all read data, which prevents it from being modified or deleted by other transactions. The locks are held until the current transaction is committed. It is possible for other transactions to read the data.

Note
The Transaction Type of the transaction within which the query is running is not affected.

If you are familiar with SQL, this mode translates to reading the data with Repeatable Read.

ReadExclusive

Reads only data that has been committed to the database.

Update locks are placed on all read data, which prevents it from being modified or deleted by other transactions. It is possible for other transactions to read the data depending on their transaction types.

Note
The Transaction Type of the transaction within which the query is running is not affected.

If you are familiar with SQL, this mode translates to reading the data with UpdLocks.