OpenEdge Data Management: DataServer for Microsoft SQL Server

Additional Features to Enhance DataServer Performance
Writing queries for performance
4–16
This section provides a collection of tips and guidelines to follow when writing queries. For
example, a query that processes a large number of rows performs best if it uses NO–LOCK,
lookahead cursors, a large cache size, and a small field list.
These tips and guidelines might improve the performance of your DataServer applications. To
assess the usefulness of a particular suggestion, apply it, then use the DEBUG diagnostic options
to gather statistics on how your application runs:
• Use FOR EACH, GET, and OPEN QUERY statements rather than FIND statements, which
generally perform more slowly. Consider using the FOR FIRST statement instead of
FIND FIRST.
The only exception is that FIND LAST is faster than GET LAST. This is because GET LAST
causes the client to process all of the records; the FIND LAST statement allows the server to
retrieve the last record.
• Use field lists.
• Use the QUERY–TUNING options.
• Use lookahead cursors.
• Use NO–LOCK where possible.
• Avoid specifying lock upgrades. Instead, allow the DataServer and the MS SQL Server
data source to handle lock upgrades.
• Do not ask for a particular ordering of results with USE–INDEX or BY clauses unless your
application requires it. Instead, allow the DataServer and the MS SQL Server data source
to determine the most efficient index (if any) for processing a query and avoid the
overhead of sorting results.
• If you use a BY clause that will sort a large amount of data, make sure a corresponding
index exists in your data source to make sorting efficient. In some cases it may also be
desirable to have indexes over columns used in WHERE clause selection criteria.
• For aggregates, use either the RUN–STORED–PROCEDURE send–sql–statement syntax or an
OpenEdge SQL statement. If you use an OpenEdge SQL statement with a cursor, declare
the cursor read-only.
• When you test for the existence of a record, use the CAN–FIND FIRST function, which does
not retrieve the record if the DataServer passes the entire WHERE clause to the MS SQL
Server data source for processing. However, avoid nesting CAN–FIND functions.
• Avoid using the RECID function. Instead, use the ROWID function.