Performance Considerations

The following connection options can enhance driver performance. You can also enhance performance through efficient application design. Refer to "Designing ODBC Applications for Performance Optimization" in the DataDirect Connect for ODBC and Connect XE for ODBC Reference for details.

The option names found on the tabs of the driver Setup dialog box are the same as the connection string attribute names unless otherwise noted in parentheses. The connection string attribute name does not have spaces between the words. For example, the option name Application Using Threads is equivalent to the connection string attribute name ApplicationUsingThreads.

Application Using Threads (ApplicationUsingThreads): The driver coordinates concurrent database operations (operations from different threads) by acquiring locks. Although locking prevents errors in the driver, it also decreases performance. If your application does not make ODBC calls from different threads, the driver has no reason to coordinate operations. Disabling the Application Using Threads option prevents the driver from coordinating operations and improves performance for single-threaded applications.

NOTE: If you are using a multi-threaded application, you must enable the Application Using Threads option.

Default Buffer Size for Long/LOB Columns (DefaultLongDataBuffLen): To improve performance when your application fetches images, pictures, or long text or binary data, a buffer size can be set to accommodate the maximum size of the data. The buffer size should only be large enough to accommodate the maximum amount of data retrieved. Otherwise, performance is reduced by transferring large amounts of data into an oversized buffer. If your application retrieves more than 1 MB of data, the buffer size should be increased accordingly.

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

Fetch Array Size (ArraySize): If the Select Method connection option is set to 0 and your application fetches more than 50 rows at a time, you should set Fetch Array Size to the approximate number of rows being fetched. This reduces the number of round trips on the network, thereby increasing performance. For example, if your application normally fetches 200 rows, it is more efficient for the driver to fetch 200 rows at one time over the network than to fetch 50 rows at a time during four round trips over the network. You should use Fetch Array Size in conjunction with Select Method.

NOTE: The ideal setting for your application will vary. To calculate the ideal setting for this option, you must know the size in bytes of the rows that you are fetching and the size in bytes of your Network Packet. Then, you must calculate the number of rows that will fit in your Network Packet, leaving space for packet overhead. For example, suppose your Network Packet size is 1024 bytes and the row size is 8 bytes. Dividing 1024 by 8 equals 128; however, the ideal setting for Fetch Array Size is 127, not 128, because the number of rows times the row size must be slightly smaller than the Network Packet size.

Packet Size (PacketSize): Typically, it is optimal for the client to use the maximum packet size that the 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 Packet Size option is set to the packet size of the Sybase server.

Prepare Method (OptimizePrepare): If your application executes the same SQL statements multiple times, performance can be improved by creating a stored procedure on the server at prepare time. If your application executes one of these prepared statements multiple times, performance will improve because the driver created a stored procedure and executing a stored procedure is faster than executing a single SQL statement; however, if a prepared statement is only executed once or is never executed, performance can decrease. If your application executes the same SQL statements multiple times, the Prepare Method option should be set to 1.

Select Method (SelectMethod): If your application often executes a SQL statement before processing or closing the previous result set, then it uses multiple active statements per connection. The default setting (0) of this option causes the driver to use database cursors for Select statements and allows an application to process multiple active statements per connection. An active statement is defined as a statement where all the result rows or result sets have not been fetched. This can cause high overhead on the server. If your application does not use multiple active statements, however, setting Select Method to 1 will increase performance of Select statements by allowing the server to return results without using a database cursor. If this option is set to 0, it should be used in conjunction with Fetch Array Size (ArraySize). If this option is set to 1, Fetch Array Size (ArraySize) has no effect.