OpenEdge Data Management: DataServer for Microsoft SQL Server

Additional Features to Enhance DataServer Performance
Enhancements overview
4–2
When you develop a DataServer application, you can design it either to emphasize portability
across data sources or to optimize the strengths of the DataServer’s interaction with a MS SQL
Server database. For example, you might write a query that gives you consistent results across
databases or one that takes advantage of MS SQL Server’s cursor management functionality.
In addition to influencing how DataServer applications perform through queries, you can
control how the DataServer processes queries on a statement-by-statement basis. Some of the
DataServer’s default behavior might not be optimal for the application you are designing. The
QUERY–TUNING phrase and startup and connection parameters give you the ability to control
query processing.
Information on query tuning appears in the following locations:
• The remaining sections of this chapter document the QUERY–TUNING phrase.
• For information on tuning queries at compile time and run time, see the “Query tuning
with connection and startup parameters” section on page 6–16.
Connection pooling
The DataServer for Microsoft SQL Server is enhanced with the ability to form a connection
pool. A connection pool is a set of database connections that are available for an application to
use and reuse without having to be reestablished. Connection pooling significantly improves the
cursor management associated with no-lock queries, particularly multi-table joins. Creating and
tearing down connections can be resource intensive. Using a pooled connection to keep existing
connections alive results in significant performance gains because the DataServer avoids the
overhead of making a connection for each request. ABL applications that open multiple no-lock
queries and handle their results simultaneously experience the best cumulative performance
gains from connection pooling.
Main components
Connection pooling for the DataServer for Microsoft SQL Server is a combination of ODBC
connection pooling and DataServer connection management. These connection components can
be used as follows:
• Individually, ODBC connection pooling or DataServer connection management provides
the foundation required for firehose cursors, but enabling both provides the best
performance. For more information on firehose cursors, see the “Firehose and Fast
Forward-Only Cursors” section on page 4–5.
Without a connection pool, firehose cursors would block an application until a full result
set is retrieved. Because of this, when connection pooling is disabled, firehose cursors are
also disabled. By maintaining multiple connections and one cursor per connection,
read-only requests only block the connection on which they retrieve results, freeing ABL
applications to continue processing data on the other connections.
• ODBC connection pooling and DataServer connection management provide the highest
performance improvements when enabled together, but they can also be enabled
independent of one another.