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Reference : Designing ODBC Applications for Performance Optimization : Selecting ODBC Functions : Using the Cursor Library
  

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Using the Cursor Library
If the driver provides scrollable cursors, do not use the cursor library. The cursor library creates local temporary log files, which are performance-expensive to generate and provide worse performance than native scrollable cursors.
The cursor library adds support for static cursors, which simplifies the coding of applications that use scrollable cursors. However, the cursor library creates temporary log files on the user’s local disk drive to accomplish the task. Typically, disk I/O is a slow operation. Although the cursor library is beneficial, applications should not automatically choose to use the cursor library when an ODBC driver supports scrollable cursors natively.
Typically, ODBC drivers that support scrollable cursors achieve high performance by requesting that the database server produce a scrollable result set instead of emulating the capability by creating log files. Many applications use:
rc = SQLSetConnectOption (hdbc, SQL_ODBC_CURSORS, SQL_CUR_USE_ODBC);
but should use:
rc = SQLSetConnectOption (hdbc, SQL_ODBC_CURSORS, SQL_CUR_USE_IF_NEEDED);