Deferred prepare in CLI applications
Deferred prepare is
a CLI feature
that minimize communication with the server by sending both the prepare
and execute requests for SQL statements in the same network flow.
The default value for this property can be overridden using the CLI/ODBC configuration
keyword DeferredPrepare. This property can be set on a per-statement
handle basis by calling SQLSetStmtAttr() to
change the SQL_ATTR_DEFERRED_PREPARE statement attribute.
When deferred prepare is on, the prepare request is not sent to
the server until the corresponding execute request is issued. The
two requests are then combined into one command/reply flow (instead
of two) to minimize network flow and to improve performance. Because
of this behavior, any errors that would typically be generated by
SQLPrepare() will
appear at execute time, and SQLPrepare() will
always return SQL_SUCCESS. Deferred prepare is of greatest benefit
when the application generates queries where the answer set is very
small, and the resource usage of separate requests and replies is
not spread across multiple blocks of query data. Note: Even if deferred
prepare is enabled, operations that require a statement to be prepared
before the operation's execution will force the prepare request to
be sent to the server before the execute. Describe operations resulting
from calls to
SQLDescribeParam() or SQLDescribeCol() are
examples of when deferred prepare will be overridden, because describe
information is only available after the statement has been prepared.