MDAC 2.5 SDK - OLE DB Providers
OLE DB Provider for Oracle

Isolation Levels

Oracle clients can control transaction-isolation levels for a connection. To control transaction-isolation level, the consumer uses the following:

• The DBPROPSET_SESSION property DBPROP_SESS_AUTOCOMMITISOLEVELS for this provider's default autocommit mode. The provider default for the level is DBPROPVAL_TI_READCOMMITTED.
  
  
• The isoLevel parameter of ITransactionLocal::StartTransaction for local manual-commit transactions.

All levels restrict concurrency by applying locks to Oracle objects. As the client requires greater concurrency levels, Oracle applies greater restrictions on concurrent access to data. To maintain the highest level of concurrent access to data, the consumer should intelligently control its requests for specific concurrency levels.

Oracle supports only the READCOMMITTED and SERIALIZABLE isolation levels. All others are promoted to these levels. In high-performance situations, SERIALIZABLE is discouraged because of the number of locks taken to achieve that level of concurrency.