MDAC 2.5 SDK - OLE DB Providers
OLE DB Provider for SQL Server

Isolation Levels in SQLOLEDB

Microsoft® SQL Server™ clients can control transaction-isolation levels for a connection. To control transaction-isolation level, the SQLOLEDB consumer uses the following elements:

• DBPROPSET_SESSION property DBPROP_SESS_AUTOCOMMITISOLEVELS for SQLOLEDB default auto-commit mode.

  The SQLOLEDB default for the level is DBPROPVAL_TI_READCOMMITTED.

• The isoLevel parameter of the ITransactionLocal::StartTransaction method for local manual-commit transactions.
  
  
• The isoLevel parameter of the ITransactionDispenser::BeginTransaction method for MS DTC-coordinated distributed transactions.

SQL Server allows read-only access at the dirty read isolation level. All other levels restrict concurrency by applying locks to SQL Server objects. As the client requires greater concurrency levels, SQL Server applies greater restrictions on concurrent access to data. To maintain the highest level of concurrent access to data, the SQLOLEDB consumer should control its requests intelligently for specific concurrency levels.

See Also

"Isolation Levels" in SQL Server Books Online