What are the locks available in Visual Basic?
Locking is the process by which a DBMS restricts access to a row in a multi-user environment
4 types of locks. They are 1. Batch Optimistic 2. Optimistic 3. Pessimistic 4. ReadOnly
Operations in a relational database act on a complete set of rows. The set of rows returned by a SELECT statement consists of all the rows that satisfy the conditions in the WHERE clause of the statement. This complete set of rows returned by the statement is known as the result set. Applications, especially those that are interactive and online, cannot always work effectively with the entire result set as a unit.
These applications need a mechanism to work with one row or a small block of rows at a time. Cursors are an extension to result sets that provide that mechanism.
Cursor or lock type Advantages Disadvantages
AdOpenForwardOnly (Default) • Low resource requirements • Cannot scroll backward • No data concurrency
AdOpenStatic • Scrollable (Wont detect changes made at the same time by another application) • No data concurrency
AdOpenKeyset • Some data concurrency • Scrollable • Higher resource requirements • Not available in disconnected scenario
AdOpenDynamic • High data concurrency • Scrollable • Highest resource requirements • Not available in disconnected scenario
AdLockReadOnly • Low resource requirements • Highly scalable • Data not updatable through cursor
AdLockBatchOptimistic • Batch updates • Allows disconnected scenarios • Other users able to access
data • Data can be changed by multiple users at once
AdLockPessimistic • Data cannot be changed by other users while locked • Prevents other users from
accessing data while locked
AdLockOptimistic • Other users able to access data • Data can be changed by multiple users at once
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What are the locks available in Visual Basic?
4 types of locks. They are 1. Batch Optimistic 2. Optimistic 3. Pessimistic 4. ReadOnly
Operations in a relational database act on a complete set of rows. The set of rows returned by a SELECT statement consists of all the rows that satisfy the conditions in the WHERE clause of the statement. This complete set of rows returned by the statement is known as the result set. Applications, especially those that are interactive and online, cannot always work effectively with the entire result set as a unit.
These applications need a mechanism to work with one row or a small block of rows at a time. Cursors are an extension to result sets that provide that mechanism.
Cursor or lock type Advantages Disadvantages
AdOpenForwardOnly (Default) • Low resource requirements • Cannot scroll backward • No data concurrency
AdOpenStatic • Scrollable (Wont detect changes made at the same time by another application) • No data concurrency
AdOpenKeyset • Some data concurrency • Scrollable • Higher resource requirements • Not available in disconnected scenario
AdOpenDynamic • High data concurrency • Scrollable • Highest resource requirements • Not available in disconnected scenario
AdLockReadOnly • Low resource requirements • Highly scalable • Data not updatable through cursor
AdLockBatchOptimistic • Batch updates • Allows disconnected scenarios • Other users able to access
data • Data can be changed by multiple users at once
AdLockPessimistic • Data cannot be changed by other users while locked • Prevents other users from
accessing data while locked
AdLockOptimistic • Other users able to access data • Data can be changed by multiple users at once
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