Matakuliah
Tahun
: T0413
: 2009
Trouble Shooting and Maintenance
Pertemuan 13
Problem Diagnosis
db2 ? <code>
Review the DB2
online manuals
(Information Center)
Problem!
Review
Admin notification log
or
the db2diag.log
Check the
DB2 Express-C forum
Review system with
Operating System
commands
Search for APARs, or
known problems
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db2 help: ?
db2
db2
db2
db2
db2
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?
?
?
?
?
SQL0104N
SQL104N
SQL-0104
SQL-104
SQL-104N
4
Finding More Information About Error Codes
• To find out more information about an error code received, in the
Command Editor input area, enter the code prefixed by a question
mark and click the Execute button
Prefix error code by
a question mark in
the Input area
More information
about the error
code appears in
the Output area
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The DB2 Information Center
•
The DB2 Information Center contains the DB2 online manuals. It also includes the
manuals of products related to DB2.
•
It has a search field
•
It can be installed locally, or accessed through the internet
•
The internet version is the most up-to-date one. The URLs are:
– V9: http://publib.boulder.ibm.com/infocenter/db2luw/v9/index.jsp
– V9.5: http://publib.boulder.ibm.com/infocenter/db2luw/v9r5/index.jsp
•
Most of the answers to your questions can be found from the DB2 Information
Center!
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DB2 Administration Notification Log
Log with diagnosis information at the point failure
On Linux/UNIX platforms, the administration notification log is a text
file called instance.nfy
On Windows, all administration notification messages are written to
the Event Log, or you can see in in the DB2 Journal
The DBM configuration parameter notifylevel specifies the level of
information to be recorded:
ƒ
ƒ
ƒ
ƒ
ƒ
0 -- No administration notification messages captured (not recommended)
1 -- Fatal or unrecoverable errors
2 -- Immediate action required
3 -- Important information, no immediate action required (default)
4 -- Informational messages
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db2diag.log
Information included in the db2diag.log




The timestamp when the error occurred. Use it to find the error quickly
The application name and DB2 function involved in the problem.
A diagnostic message explaining the reason for the error.
Any available supporting data, such as SQLCA data structures and
pointers to the location of any extra dump or trap files.
If you can recreate the problem:
 Remove/rename the db2diag.log
 Recreate the problem. A new db2diag.log file will be generated
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Example of a db2diag.log entry
Timestamp when the problem occurred
Level: Be concerned when you see
“Severe” or “Error” here.
Application name
Error message information. Use any of these for searching in “Google”
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Locating the db2diag.log
WIN XP/2003 (default)
C:\Documents and Settings\All Users\Application Data\IBM\DB2\DB2COPY1\<instance name>
ƒWIN VISTA
ƒ ProgramData\IBM\DB2\
Linux/UNIX (default)
INSTHOME/sqllib/db2dump (INSTHOME is the home directory of the instance owner)
You can change the location of the db2diag.log using diagpath in the dbm cfg
ƒ db2 update dbm cfg using diagpath <path>
The verbosity of diagnostic text is determined by diaglevel in the dbm cfg
ƒ range is 0 to 4 (default is 3)
ƒ most verbose is 4
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The DB2 Express-C Forum
Free community assistance
www.ibm.com/developerworks/forums/dw_forum.jsp?forum=805&cat=19
Mainly in English
The IBM DB2 Express-C team monitors the forum, though it is
the community who assists the most
You can also access it from the DB2 Express-C web site:
www.ibm.com/db2/express
(and click the button to go to the forum)
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Maintenance Utilities
REORG, RUNSTATS, REBIND
REORG
RUNSTATS
REBIND
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Database Operational View in Control Center
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Table Reorganization (REORG)
•
•
•
•
Over time, tables and indexes get fragmented (much like a file system)
A REORG reclaims wasted space and re-organizes data to make
retrieval more efficient
Tables that are modified the most will benefit the most from REORGs
REORG has an Online and Offline option
– Offline REORG is faster and more efficient, but does not permit
access to the table
– Online REORG allows access to the table, but can consume a lot
of system resources; it works best for small tables
REORG TABLE <tablename>
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Example:
REORG TABLE employee
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Statistics (RUNSTATS)
• Keeps database statistics up-to-date
– e.g. number of rows in a table, index size, data value ranges,
etc.
• Statistics are used by DB2 whenever queries are executed
– DB2 Query Optimizer is a cost-based optimizer
– Analyzes these statistics to produce data access plan
• The frequency of statistics gathering should be determined by how
often the data in the table changes
RUNSTATS ON TABLE <schema.tablename>
Example:
RUNSTATS ON TABLE myschema.employee
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RUNSTATS and REORG from the Control
Center
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Control Center > (expand) All Databases folder > (expand) Database > (select) Tables Folder > (right-click)
Table > Reorganize/Run Statistics
Bind/Rebind Packages
 Applies to embedded SQL applications, SQL stored procedures
 Static SQL application depicted
embedded
C program
(.sqc)
Access plans for
static SQL are
determined at
BIND time
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C file
(.c)
library
.exe
bind file
(.bnd)
package
17
REBIND
db2rbind database_alias -l <logfile>
Example:
db2rbind sample -l mylog.txt
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Maintenance Choices
• Automated Maintenance
– Have DB2 automatically look after maintenance for you
(REORG, RUNSTATS, BACKUP)
• Manual Maintenance
– You perform maintenance activities when the need arises
• Create Scripts to Perform Maintenance
– Schedule regular execution of scripts
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Automated Maintenance
•
Based on a user-defined maintenance window
– DB2 will perform maintenance on this window ONLY if needed.
– Two maintenance windows:
• ONLINE: For online maintenance activities such as
RUNSTATS and online BACKUP. These can be defined at
any time because the database remains fully accessible
• OFFLINE: For offline maintenance activities such as offline
BACKUP and REORG. Database may become inaccessible
and any connected applications may be affected.
– Database keeps track of operations performed and schedules
any needed maintenance in the next appropriate maintenance
window
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Scheduled Maintenance Using Task Center
• More time-consuming than automatic
maintenance, but more customization possibilities
– E.g. different tables might have different backup
needs
• Task Center is the central location for all
scheduled activities for the DB2 administration
tools
– It is the main interface where all tasks can be
created, edited, and scheduled
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Performance
• Configure parameters
– Use the Configuration Advisor
– The bufferpool is the most important parameter to configure
• This is like cache for databases
• Do not over allocate physical memory to the bufferpool
• Design good indexes
– Use the Design Advisor
– Indexes can reduce sorts
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Performance
• Choose the right locking strategy
– Depending on your application logic choose the appropriate
isolation level. UR provides the most concurrency.
• Reduce deadlocks by minimizing:
– Repeatable Read isolation
– Lock Escalation
– Lock Conversion
– Bad Access plans (table scans)
– Catalog Modification
– Referential Constraint Enforcement
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Performance
• Minimize network traffic
– Use stored procedures
– Limit the fetch size using clauses like:
• Optimize for X rows: Use this clause to determine the
best communications buffer size.
• fetch first x rows only: Limit on the number of rows
retrieved
Eg:
SELECT EMPNAME, SALARY FROM
EMPLOYEE
ORDER BY SALARY DESC
FETCH FIRST 100 ROWS ONLY
OPTIMIZE FOR 20 ROWS
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Performance
• Dynamic vs. Static SQL
– Static SQL performs better than dynamic SQL
– If must use dynamic SQL, ensure to use parameter markers
• Code your SQL appropriately
– Don’t ask for more than you need
• For example, asking for all the columns is not good, like
in: Select * from …
– Analyze bad performing SQL with Visual Explain
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Visual ExplainAccess Plan
Execute &
Access Plan
Statement to
analyze
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Visual Explain
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