Territory code of database: 1
  Server instance name: DB2
                                                                          
                                                                          
  Database Name: SAMPLE
  Database Path: C:\DB2\NODE0000\SQL00001\
  First connection timestamp: 02 01 2004 13:25:43.028006
  Event Monitor Start time:   02 06 2003 09:51:57.663712
                                                                          
3) Deadlock Event ...
  Deadlock ID:   4
  Number of applications deadlocked: 2
  Deadlock detection time: 02 06 2003 09:53:11.952919
  Rolled back Appl participant no: 2
  Rolled back Appl Id: *LOCAL.DB2.010686063633
  Rolled back Appl seq number: : 0005
[...]
Visual Explain
Visual Explain
 is used to capture and view information about the access plan 
chosen by the 
DB2 optimizer
 for SQL statements as a graph. An access plan is 
a cost estimation of resource usage for a query, which is based on the available 
information such as statistics for tables and indexes, instance and database 
configuration parameters, bind options and query optimization level, and so on. 
An access plan also specifies the order of operations for accessing the data.
The access plan acquired from Visual Explain helps to understand how individual 
SQL statements are executed. The information available from the Visual Explain 
graph can be used to tune the SQL queries for better performance.
To start Visual Explain, launch the 
Control Center
, right click the database name 
and select either the 
Explain SQL 
or 
Show Explained Statements History
option. You can input an SQL statement manually or import the SQL statement 
through the 
Get 
button available in the Explain SQL window. You can also specify 
the optimization class for the SQL statement in the same window. The 
optimization class implies the effort the DB2 optimizer will spend on preparing 
the execution plan (higher value means more sophisticated optimization). 
Figure 9 5 shows an example of an access plan graph. 
 Chapter 9. Testing and tuning 
295






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