IBM ^ iSeries

© 2003 IBM Corporation

DB2 UDB for iSeries – The new Architecture

Sabine JordaniSeries Technical Support

DB2 UDB on iSeries

© 2003 IBM Corporation1

Trademarks & Disclaimer

! Course content and examples are based upon Version 5 Release 2 of OS/400 and DB2 UDB for iSeries. System and application behavior may be different on other releases of OS/400 and DB2 UDB.

! Example queries may not compile or run.! NOTICE: this publication may refer to products that are not currently available in your

country.! IBM makes no commitment to make available any products referred to herein.! IBM, eServer, iSeries, AS/400, OS/400 and DB2 are trademarks of the IBM Corporation

in the United States or other countries or both.! Other company, product, and service names may be trademarks or service marks of

others.! Java and all java-based trademarks and logos are trademarks of Sun Microsystems,

Inc. In the United States and/or other countries.! IBM’s VisualAge products and services are not associated with or sponsored by Visual

Edge software, ltd.! A list of trademarks may be found on the worldwide web:

http://www.ibm.com/trademarks.html

DB2 UDB on iSeries

© 2003 IBM Corporation2

V5R1 Database Architecture

SQLSQL

Static

Compiled embedded statements

Extended DynamicPrepare once

and then reference

Dynamic

Prepare every time

DB2 UDB(Data Storage & Management)

DB2 UDB(Data Storage & Management)

Host ServerHost Server CLI / JDBCCLI / JDBC

OptimizerOptimizer

ODBC / JDBC / ADO / DRDA / XDAODBC / JDBC / ADO / DRDA / XDA

Native(Record I/O)

Native(Record I/O)

NetworkNetwork

The optimizer and database engine are

separated at different layers of

the operating system

TIMI

DB2 UDB on iSeries

© 2003 IBM Corporation3

V5R2 Database Architecture

Optimizer

Query Dispatcher

CQE (Classic Query Engine)

Optimizer

SQE Optimizer

SLICDB2 UDB (Data Storage & Management)

SQE Optimizer

CQE Database Engine

SQE Primitives

SQE Statistic Manager

The optimizer and database engine

merged to form the SQL Query Engine and much of the

work was moved to SLIC

DB2 UDB on iSeries

© 2003 IBM Corporation4

What’s in a Name

! DB2 UDB for iSeries represents entire integrated database

! Optimizer now determines which engine will handle specific query – Classic Query Engine (CQE)

– SQL Query Engine (SQE)

! Still only one interface into Optimizer

DB2 UDB on iSeries

© 2003 IBM Corporation5

Query Dispatcher

D A T AD A T A S Q EC Q E

System Licensed Internal Code (SLIC)

Parts of the SQE Optimizer now reside in SLIC

Query Dispatcher

Optimizer

Non-SQL InterfacesOPNQRYFQuery/400

QQQQry API

Non-SQL InterfacesOPNQRYFQuery/400

QQQQry API

SQL Based InterfacesODBC / JDBC / CLI

Embedded & Interactive SQLRun SQL ScriptsQuery Manager

Net.DataRUNSQLSTM

SQL Based InterfacesODBC / JDBC / CLI

Embedded & Interactive SQLRun SQL ScriptsQuery Manager

Net.DataRUNSQLSTM

S Q EC Q E

DB2 UDB on iSeries

© 2003 IBM Corporation6

What goes to CQE?

– >1 Table (i.e. no joins)

– OR & IN predicates

– SMP requested

– Non-Read (INSERT with subselect can use new path)

– LIKE predicates

– UNIONS

– View or Logical File references

– Subquery

– Derived Tables & Common Table expressions

– LOB columns

– NLSS/CCSID translation between columns

– DB2 Multisystem

– Non-SQL queries (QQQQry API, Query/400, OPNQRYF)

New features PTF’d into V5R2 1H2003

DB2 UDB on iSeries

© 2003 IBM Corporation7

SQE Optimizer

! Finds best way to implement given query! No knowledge of metadata or system capabilities

– Asks questions on these factors

– Separation of responsibilities between Optimizer and Statistics Manager

! Access Plans organized in tree based structure! Responsible for collecting and processing

feedback information

DB2 UDB on iSeries

© 2003 IBM Corporation8

SQE Primitives

! Provide actual implementation of given query! More aggressive on using I/O subsystems and

main memory! Redesign of many data access methods

– Less CPU consumption

– New algorithms for distinct and SMP processing

! Temporary results retooled to eliminate need for a “true” database object to be created

DB2 UDB on iSeries

© 2003 IBM Corporation9

Statistics Manager

! Controls access to meta data used for query optimization– Does not run or optimize query

! Answers questions from Optimizer– Accuracy of answers dictates Optimizer’s ability to find

best plan

– Must always provide an answer

! Answers are derived from different sources

DB2 UDB on iSeries

© 2003 IBM Corporation10

Types of statistics questions

How many I/O’s will be required to process this table or index?I/O estimates

What indexes exist over a given table and what keys are interesting?Meta-data

How many records exist within a table?Meta-data

How many distinct occurrences of a value exist for a single column or multiple columns in a query?Cardinality

How many records will be selected by a given selection predicate or combination of predicates?Selectivity

DescriptionType of Question

DB2 UDB on iSeries

© 2003 IBM Corporation11

Sources for Answers

! Meta data sources– Existing indexes (radix or EVI)

– Information in physical objects (tables…)

– System information

! Default values – No representation of actual data

! Single Column Statistics NEW

DB2 UDB on iSeries

© 2003 IBM Corporation12

Column Cardinality

The number of distinct values in a column.

DB2 UDB on iSeries

© 2003 IBM Corporation13

Histograms

Distribution statistic that describes the selectivity and the distribution of values for a given column.

DB2 UDB on iSeries

© 2003 IBM Corporation14

Most Frequent Values List

A table of values that most frequently occurs within a column and a count of their frequency.

DB2 UDB on iSeries

© 2003 IBM Corporation15

Automatic Statistics Collection

! Automatic collection performed by default! Automatic update of collected column statistics

– > 15% change in number of records

– > 15% of records in table changed

– Checked when stats are used

! Performed as background job (QDBFSTCCOL)– Priority 90 to 99

– Low priority I/O

– Job goes to wait when higher priority job needs CPU

DB2 UDB on iSeries

© 2003 IBM Corporation16

Statistics Collection Interface

! Systemvalue QDBFSTCCOL controls automatic collection– *ALL

– *NONE

– *USER

– *SYSTEM

! iSeries Navigator graphical interface to column statistics– APIs available for use in programms

DB2 UDB on iSeries

© 2003 IBM Corporation17

Plan Cache

! Caches all plans optimized by SQE Optimizer– More reuse of plans regardless of interfaces

– Works in conjunction with systemwide statement cache, SQL programs and SQL packages

! Self managed– User doesn’t have to do any housekeeping

! Plan Cache is cleared at IPL

DB2 UDB on iSeries

© 2003 IBM Corporation18

Plan Cache Example

Plan A

Plan B

Plan C

Statement 1Statement 2

Statement 3Statement 4

Statement 3Statement 6

SQL Pgm X

SQL Package 1

SQL Package 2

Plan Cache

DB2 UDB on iSeries

© 2003 IBM Corporation19

Feedback Differences

! New DBMON records for stats feedback(QQRID 3015)

! QQC16 in 3014 record shows use of SQE (Y/N)! Optimizer may not recommend all possibly helpful

indexes! Optimizer recommends index creation without

checking whether they are already there! Order of debug messages / DBMON records may

be different

DB2 UDB on iSeries

© 2003 IBM Corporation20

How do I get it?

! All V5R2 systems take advantage of SQE! Code was refreshed via PTFs in May 2003

– Currently DB group PTF 9

– SI07650

! Refer to following website for availability of PTFsrequired for SQE– http://www.iseries.ibm.com/db2/sqe.html

DB2 UDB on iSeries

© 2003 IBM Corporation21

Additional Information

! Redbook “Preparing for and Tuning the V5R2 SQL Query Engine” – SG24-6598

! http://www.iseries.ibm.com/db2 (DB2 for iSerieshomepage)

! http://www.iseris.ibm.com/db2/books.htm (DB2 for iSeries manuals)