Performance Considerations

The following connection options can enhance driver performance. You can also enhance performance through efficient application design. Refer to Chapter 5 “Designing ODBC Applications for Performance Optimization” in the DataDirect Connect Series for ODBC Reference for details.

Connection Pooling (ConnectionPooling): If you enable the driver to use connection pooling, you can set additional options that affect performance:

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Load Balance Timeout: You can define how long to keep connections in the pool. The time that a connection was last used is compared to the current time and, if the timespan exceeds the value of the Load Balance Timeout option, the connection is destroyed. The Min Pool Size option can cause some connections to ignore this value.

■	Connection Reset: Resetting a re-used connection to the initial configuration settings impacts performance negatively because the connection must issue additional commands to the server.

■	Max Pool Size: Setting the maximum number of connections that the pool can contain too low might cause delays while waiting for a connection to become available. Setting the number too high wastes resources.

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Min Pool Size: A connection pool is created when the first connection with a unique connection string connects to the database. The pool is populated with connections up to the minimum pool size, if one has been specified. The connection pool retains this number of connections, even when some connections exceed their Load Balance Timeout value.

Enable Bulk Load (EnableBulkLoad): If your application performs bulk loading of data, you can improve performance by configuring the driver to use the database system's bulk load functionality instead of database array binding. The trade-off to consider for improved performance is that using the bulk load functionality can bypass data integrity constraints.

Encryption Method (EncryptionMethod): Data encryption may adversely affect performance because of the additional overhead (mainly CPU usage) that is required to encrypt and decrypt data.

Failover Mode (FailoverMode): Although high availability that replays queries after a failure provides increased levels of protection, it can adversely affect performance because of increased overhead.

Packet Size (PacketSize): Typically, it is optimal for the client to use the maximum packet size that the database server allows. This reduces the total number of round trips required to return data to the client, thus improving performance. Therefore, performance can be improved if the PacketSize attribute is set to the maximum packet size of the server.

Use Snapshot Transactions (SnapshotSerializable): You must have your Microsoft SQL Server 2005 and higher database configured for snapshot isolation for this connection option to work. Snapshot Isolation provides transaction-level read consistency and an optimistic approach to data modifications by not acquiring locks on data until data is to be modified. This Microsoft SQL Server 2005 and higher feature can be useful if you want to consistently return the same result set even if another transaction has changed the data and 1) your application executes many read operations or 2) your application has long running transactions that could potentially block users from reading data. This feature has the potential to eliminate data contention between read operations and update operations. When this connection option is enabled, performance is improved due to increased concurrency.

See “Using The Snapshot Isolation Level” for details.