Chapter 2. DB2 Universal Database for iSeries performance basics 15
2.2.1 Database architecture before V5R2M0
For systems prior to the release of V5R2M0, all database requests are handled by the CQE.
Figure 2-3 shows a high-level overview of the architecture of DB2 Universal Database for
iSeries before OS/400 V5R2. The optimizer and database engine are implemented at
different layers of the operating system.
Figure 2-3 Database architecture before the release of V5R2M0: Classic Query Engine
Most CQE query decisions are made above the machine interface (MI) level. In CQE, the
interaction between the optimizer and the query execution component occurs across the MI,
resulting in interface-related performance overhead.
2.2.2 Current database architecture
With the release of V5R2M0, a new SQE was shipped. SQE and CQE coexist in the same
database environment. Depending on the database requests, the Query Dispatcher (see
2.2.3, “Query Dispatcher” on page 17) decides to route the query to either the CQE or SQE.
While both the new SQE and the existing CQE can handle queries from start to finish, the
redesigned engine simplifies and speeds up queries. In addition to providing the same
functionality as CQE, SQE also performs these functions:
Moves the optimizer below the MI for more efficient query processing
Separates and moves improved statistics to the Statistics Manager dashboard
Uses an object-oriented design that accelerates the delivery of new database functionality
Uses more flexible, independent data access options to provide autonomous query cruise
Uses enhanced algorithms to provide greater responsiveness and query handling
Provides enhanced performance on long-running complex query terrains
Retains road maps to provide ease of use in query driving
Provides additional and enhanced query feedback and debug information messages
through the Database Monitor and Visual Explain interfaces
DB2 Universal Database
(Data Storage and Management)
Host Server CLI/JDBC
Machine Interface (MI)
The optimizer and
are separated at
different layers of