OpenEdge Data Management: DataServer for Microsoft SQL Server

Additional Features to Enhance DataServer Performance
Table 4–1: Query-tuning options (3 of 3)
4–12
Option Description
FIREHOSE-CURSOR Specifies at the query level that the firehose cursor type should be
considered to satisfy the query when the NO-LOCK phrase is used.
Note: This query-level option overrides the connection-level
-Dsrv options, QT_FIREHOSE and QT_NO_FIREHOSE that determine
if firehose cursors should be considered for the DataServer
connection.
NO-FIREHOSE-CURSOR Specifies at the query level that the firehose cursor type should
not be considered to satisfy the query when the NO-LOCK phrase is
used.
Notes:This query-level option overrides the connection-level
-Dsrv options, QT_FIREHOSE and QT-NO-FIREHOSE that determine
if firehose cursors should be considered for the DataServer
connection.
By default, firehose cursors are available to satisfy NO-LOCK
queries during a DataServer session. It is generally
recommended this default use be retained and overridden by
QT-NO-FIREHOSE on an individual query basis in the event that
slow query performance is observed on a very large result set.
All but two of the QUERY–TUNING options take effect at both compile time and run time. The
exceptions are JOIN–BY–SQLDB and NO–JOIN–BY–SQLDB, which apply only at compile time. You
can override query-tuning defaults (except JOIN–BY–SQLDB) at run-time by specifying the
appropriate startup parameters.
The following example shows how to use the QUERY–TUNING phrase to enhance performance. It
includes a join, JOIN-BY-SQLDB, that the DataServer instructs the MS SQL Server data source
to perform by default, as shown:
FOR EACH customer, EACH order OF customer WHERE order.ordernum GT 20
BY customer.custnum QUERY-TUNING (JOIN-BY-SQLDB)
The QUERY–TUNING options in this example specify the following:
• Lookahead cursors are not used (the NO–LOOKAHEAD option)
• The DataServer writes an extended report on the SQL statements that it executes (the
DEBUG EXTENDED option)
When the DataServer constructs queries for a MS SQL Server data source, it uses the
QUERY–TUNING options that you specify as guidelines. This is because there might be syntax
considerations that prevent the DataServer from applying the QUERY–TUNING options as
specified. In such a case, the DataServer executes the query using the most appropriate options.
Note: The DataServer does not issue errors or warnings if it does not apply the
QUERY–TUNING options that you specify.